Directory of Open Access Journals (Sweden)
Yujiao Zeng
2014-01-01
Full Text Available This study presents a novel hybrid multiobjective particle swarm optimization (HMOPSO algorithm to solve the optimal reactive power dispatch (ORPD problem. This problem is formulated as a challenging nonlinear constrained multiobjective optimization problem considering three objectives, that is, power losses minimization, voltage profile improvement, and voltage stability enhancement simultaneously. In order to attain better convergence and diversity, this work presents the use of combing the classical MOPSO with Gaussian probability distribution, chaotic sequences, dynamic crowding distance, and self-adaptive mutation operator. Moreover, multiple effective strategies, such as mixed-variable handling approach, constraint handling technique, and stopping criteria, are employed. The effectiveness of the proposed algorithm for solving the ORPD problem is validated on the standard IEEE 30-bus and IEEE 118-bus systems under nominal and contingency states. The obtained results are compared with classical MOPSO, nondominated sorting genetic algorithm (NSGA-II, multiobjective evolutionary algorithm based on decomposition (MOEA/D, and other methods recently reported in the literature from the point of view of Pareto fronts, extreme, solutions and multiobjective performance metrics. The numerical results demonstrate the superiority of the proposed HMOPSO in solving the ORPD problem while strictly satisfying all the constraints.
Performance of two modified optimization techniques for power system voltage stability problems
Directory of Open Access Journals (Sweden)
S. Harish Kiran
2016-09-01
Full Text Available The development of optimization techniques in power system is to determine the sizing of Flexible AC Transmission System (FACTS devices such as Unified Power Flow Series Compensator (UPFC controller in improving the voltage stability and bus voltage margin. An attempt is made to modify the Particle Swarm Optimization (PSO and Artificial Bee Colony (ABC with Hybrid-Genetic Algorithm (H-GA for determination of sizing of the device. Fast Voltage Stability Index (FVSI is used to identify the location of the device to be connected. The proposed methods are implemented in IEEE 30 Bus system and its results are tabulated for each technique.
Practical considerations in voltage stability assessment
Energy Technology Data Exchange (ETDEWEB)
Kundur, P.; Gao, B. [Powertech Labs. Inc., Surrey, BC (Canada)
1994-12-31
This paper deals with some of the most important practical issues related to voltage stability assessment of large practical systems. A brief discussion of the practical aspects of voltage stability problem and prevention of voltage instability is given first, followed by descriptions of different analytical techniques and tools for voltage stability analysis. Presentations of analytical tools is focused on the VSTAB program which incorporates the modal analysis, continuation power flow, and shortest distance to instability techniques, Finally, an example case study of a practical large system is presented. The case study illustrates how modal analysis is used to determine the most effective load shedding scheme for preventing voltage instability. (author) 15 refs., 2 figs., 2 tabs.
Reliability criteria for voltage stability
Energy Technology Data Exchange (ETDEWEB)
Taylor, Carson W.; Silverstein, Brian L. [Bonneville Power Administration, Portland, OR (United States)
1994-12-31
In face of costs pressures, there is need to allocate scare resources more effectively in order to achieve voltage stability. This naturally leads to development of probabilistic criteria and notions of rick management. In this paper it is presented a discussion about criteria for long term voltage stability limited to the case in which the time frames are topically several minutes. (author) 14 refs., 1 fig.
VOLTAGE STABILITY IMPROVEMENT IN POWER SYSTEM BY USING STATCOM
Directory of Open Access Journals (Sweden)
A.ANBARASAN
2012-11-01
Full Text Available Voltage stability problems usually occur in heavily loaded systems. Nowadays the power demand increases enormously, hence in a large interconnected power system network subject to stress conditions. This situation can be handled by increasing the generation or reducing the transmission losses. When the load increases suddenly, voltage magnitude also varies beyond the permissible voltage stability limit. But the voltage magnitude must be maintained within the limit for proper operation of the system. Hence, voltage stability must be improved by providing suitable reactive power compensation. The proposed work was analyzed using IEEE 14 bus test system. The STATCOM improves the voltage stability margin of the system.
考虑电压稳定的无功优化问题分析%Wattless optimization problems considering voltage stability analysis
Institute of Scientific and Technical Information of China (English)
李金炜
2014-01-01
The study of voltage stability and optimal reactive power control has important significance.This paper introduces a detailed analysis of voltage stability and optimal reactive power control to specific combination modes.Meanwhile,the corresponding measures for prevention and control are put forward according to the voltage stability of system operating point,which can guide the voltage stability problems.%目前，诸多学者和工作者都在研究电压稳定性的无功优化控制，该研究成为热点问题。本文详细分析了电压稳定和无功优化控制具体结合方式。同时，针对系统运行点电压稳定提出了相应的预防控制措施，从而能够指导电压稳定问题。
Convex Relaxation of Power Dispatch for Voltage Stability Improvement
DEFF Research Database (Denmark)
Pedersen, Andreas Søndergaard; Blanke, Mogens; Jóhannsson, Hjörtur
2015-01-01
A method for enhancing the voltage stability ofa power system is presented in this paper. The method isbased on a stability-constrained optimal power flow approach,where dispatch is done such that a maximum L-index isminimised for all load busses in a transmission grid. It isshown that optimal...... dispatch is obtainable with enhancedmargins for voltage stability using a semidefinite relaxation ofthe optimal power flow problem, and that this problem canbe formulated as semidefinite program with a quasi-convexobjective. Numerical tests are performed on the IEEE-30 busand BPA systems. The feasibility...... of the method is demonstratedthrough demonstrating that improved voltage stability marginsare obtained for both systems....
Static Voltage Stability Analysis by Using SVM and Neural Network
Directory of Open Access Journals (Sweden)
Mehdi Hajian
2013-01-01
Full Text Available Voltage stability is an important problem in power system networks. In this paper, in terms of static voltage stability, and application of Neural Networks (NN and Supported Vector Machine (SVM for estimating of voltage stability margin (VSM and predicting of voltage collapse has been investigated. This paper considers voltage stability in power system in two parts. The first part calculates static voltage stability margin by Radial Basis Function Neural Network (RBFNN. The advantage of the used method is high accuracy in online detecting the VSM. Whereas the second one, voltage collapse analysis of power system is performed by Probabilistic Neural Network (PNN and SVM. The obtained results in this paper indicate, that time and number of training samples of SVM, are less than NN. In this paper, a new model of training samples for detection system, using the normal distribution load curve at each load feeder, has been used. Voltage stability analysis is estimated by well-know L and VSM indexes. To demonstrate the validity of the proposed methods, IEEE 14 bus grid and the actual network of Yazd Province are used.
Global Transient Stability and Voltage Regulation for Multimachine Power Systems
DEFF Research Database (Denmark)
Gordon, Mark; Hill, David J.
2008-01-01
This paper addresses simultaneously the major fundamental and difficult issues of nonlinearity, uncertainty, dimensionality and globality to derive performance enhancing power system stability control. The main focus is on simultaneous enhancement of transient stability and voltage regulation...... law is implemented to coordinate transient stabilizer and voltage regulator for each machine. Digital simulation studies show that global control scheme achieves unified transient stability and voltage regulation in the presence of parametric uncertainties and significant sudden changes in the network...... of power systems. This problem arises from the practical concern that both frequency and voltage control are important indices of power system control and operation but they are ascribed to different stages of system operation, i.e. the transient and post transient period respectively. The Direct Feedback...
A Review on Power System Voltage Stability and Optimization Techniques
Directory of Open Access Journals (Sweden)
T. Madhuranthaka
2016-11-01
Full Text Available Power system voltage stability is a one of the major focused areas in recent days due to mismatch between generation and demand. Maintenance of voltage stability is a challenging issue in planning and security assessment of power systems. Voltage stability is the ability of a power system to maintain steady acceptable voltages at all buses in the power system under normal operating conditions and after being subjected to a disturbance. Long-term voltage instability problems can occur in heavily loaded systems where the electrical distance is large between the generator and the load. Timely application of reactive power compensation or load shedding may prevent this type of voltage instability. System reactive power handling capacity can be improved with Flexible AC Transmission System (FACTS devices. Identification of critical system locations to undertake appropriate remedial measures in operation is the concern. This paper reviews the performance of various types FACTS controllers in power system voltage stability problem and focuses on different optimization methods implemented for optimal placement and sizing of FACTS devices to minimize power losses.
Wind Power Plant Voltage Stability Evaluation: Preprint
Energy Technology Data Exchange (ETDEWEB)
Muljadi, E.; Zhang, Y. C.
2014-09-01
Voltage stability refers to the ability of a power system to maintain steady voltages at all buses in the system after being subjected to a disturbance from a given initial operating condition. Voltage stability depends on a power system's ability to maintain and/or restore equilibrium between load demand and supply. Instability that may result occurs in the form of a progressive fall or rise of voltages of some buses. Possible outcomes of voltage instability are the loss of load in an area or tripped transmission lines and other elements by their protective systems, which may lead to cascading outages. The loss of synchronism of some generators may result from these outages or from operating conditions that violate a synchronous generator's field current limit, or in the case of variable speed wind turbine generator, the current limits of power switches. This paper investigates the impact of wind power plants on power system voltage stability by using synchrophasor measurements.
Voltage stability, bifurcation parameters and continuation methods
Energy Technology Data Exchange (ETDEWEB)
Alvarado, F.L. [Wisconsin Univ., Madison, WI (United States)
1994-12-31
This paper considers the importance of the choice of bifurcation parameter in the determination of the voltage stability limit and the maximum power load ability of a system. When the bifurcation parameter is power demand, the two limits are equivalent. However, when other types of load models and bifurcation parameters are considered, the two concepts differ. The continuation method is considered as a method for determination of voltage stability margins. Three variants of the continuation method are described: the continuation parameter is the bifurcation parameter the continuation parameter is initially the bifurcation parameter, but is free to change, and the continuation parameter is a new `arc length` parameter. Implementations of voltage stability software using continuation methods are described. (author) 23 refs., 9 figs.
Voltage Stability Evaluation Incorporating Wind Power Intermittency
Institute of Scientific and Technical Information of China (English)
Libao SHI; Yang ZHAO; Yixin NI; Liangzhong YAO; Masoud BAZARGAN
2013-01-01
A simulation framework is proposed to evaluate the voltage stability of power systems incorporating wind power intermittency.Firstly,the power output modelings of three types of wind turbines are discussed.Secondly,the Jensen model is employed to simulate the wind farm with the wake effect.The Monte Carlo based technique is used to conduct the voltage stability evaluation incorporating the randomness of the wind speed based on the Weibull probability distribution.Thirdly,the relative sensitivity index (RSI) is calculated to identify weak buses during analysis.Finally,case studies with different simulation scenarios are carried out.Some statistical results involving weakness probability,expected value and variance of RSI as well as preliminary conclusions are drawn based on numerical simulation results.
Dynamic Analysis of Power System Voltage Stability.
Gebreselassie, Assefa
This thesis investigates the effects of loads and voltage regulators on the dynamic voltage stability of power systems. The analysis focuses on the interactions of machine flux dynamics with loads and voltage control devices. The results are based on eigenvalue analysis of the linearized models and time simulation of the nonlinear models, using models from the Power System Toolbox, a Matlab -based package for the simulation and small signal analysis of nonlinear power systems. The voltage stability analysis results are developed using a single machine single load system with typical machine and network parameters and the NPCC 10-machine system. Dynamic models for generators, exciters and loads are used. The generator is modeled with a pair of poles and one damper circuit in both the d-axis and the q-axis. Saturation effects are included in the model. The IEEE Type DC1 DC commutator exciter model is used for all the exciters. Five different types of loads: constant impedance, constant current, constant power, a first order induction motor model (slip model) and a third order induction motor model (slip-flux model) are considered. The modes of instability and the stability limits of the different representation of loads are examined for two different operating modes of the exciters. The first, when all the exciters are on automatic control and the second when some exciters are on manual control. Modal participation factors are used to determine the characteristics of the critical modes. The characteristics of the unstable modes are verified by performing time simulation of the nonlinear models. Oscillatory and non-oscillatory instabilities are experienced by load buses when all the exciters are on automatic control and some exciters are on manual control respectively, for loads which are predominantly constant power and induction motors. It is concluded that the mode of instability does not depend on the type of loads but on the operating condition of the exciters
Memristor-integrated voltage-stabilizing supercapacitor system.
Liu, Bin; Liu, Boyang; Wang, Xianfu; Wu, Xinghui; Zhao, Wenning; Xu, Zhimou; Chen, Di; Shen, Guozhen
2014-08-06
Voltage-stabilized supercapacitors: A single supercapacitor formed with PCBM/Pt/IPS nanorod-array electrodes is designed and delivers enhanced areal capacitance, capacitance retention, and excellent electrical stability under bending, while a significant voltage-decrease is observed during the discharging process. Once integrated with the memristor, the memristor-integrated supercapacitor systems deliver an extremely low voltage-drop, indicating greatly enhanced voltage-stabilizing features.
Voltage stability in low voltage microgrids in aspects of active and reactive power demand
Directory of Open Access Journals (Sweden)
Parol Mirosław
2016-03-01
Full Text Available Low voltage microgrids are autonomous subsystems, in which generation, storage and power and electrical energy consumption appear. In the paper the main attention has been paid to the voltage stability issue in low voltage microgrid for different variants of its operation. In the introduction a notion of microgrid has been presented, and also the issue of influence of active and reactive power balance on node voltage level has been described. Then description of voltage stability issue has been presented. The conditions of voltage stability and indicators used to determine voltage stability margin in the microgrid have been described. Description of the low voltage test microgrid, as well as research methodology along with definition of considered variants of its operation have been presented further. The results of exemplary calculations carried out for the daily changes in node load of the active and reactive power, i.e. the voltage and the voltage stability margin indexes in nodes have been presented. Furthermore, the changes of voltage stability margin indexes depending on the variant of the microgrid operation have been presented. Summary and formulation of conclusions related to the issue of voltage stability in microgrids have been included at the end of the paper.
Voltage Stability Improvement of Grid Connected Wind Driven Induction Generator Using Svc
Directory of Open Access Journals (Sweden)
Ruchi Aggarwal
2014-05-01
Full Text Available Voltage stability is one of the major problem associated with wind power generating system which may be due to fluctuating nature of wind, heavy load, fault occurrence or insufficient reactive power supply. The wind power generating system most commonly employed with squirrel cage induction generator(SCIG that needs the support of an external device such as capacitor bank, FACTS devices etc. to support reactive power in order to remain connected with the grid during voltage dips. The voltage stability of a wind driven induction generator can be improved by using FACTS devices such as SVC, STATCOM.In this paper svc is used for voltage stability improvement.
Directory of Open Access Journals (Sweden)
Heng-Yi Su
2016-01-01
Full Text Available This paper proposes an optimal control scheme based on a synchronized phasor (synchrophasor for power system secondary voltage control. The framework covers voltage stability monitoring and control. Specifically, a voltage stability margin estimation algorithm is developed and built in the newly designed adaptive secondary voltage control (ASVC method to achieve more reliable and efficient voltage regulation in power systems. This new approach is applied to improve voltage profile across the entire power grid by an optimized plan for VAR (reactive power sources allocation; therefore, voltage stability margin of a power system can be increased to reduce the risk of voltage collapse. An extensive simulation study on the IEEE 30-bus test system is carried out to demonstrate the feasibility and effectiveness of the proposed scheme.
Influence of current limitation on voltage stability with voltage sourced converter HVDC
DEFF Research Database (Denmark)
Zeni, Lorenzo; Jóhannsson, Hjörtur; Hansen, Anca Daniela;
2013-01-01
A first study of voltage stability with relevant amount of Voltage Sourced Converter based High Voltage Direct Current (VSC-HVDC) transmission is presented, with particular focus on the converters’ behaviour when reaching their rated current. The detrimental effect of entering the current...
Voltage stability and controllability indices for multimachine power systems
Energy Technology Data Exchange (ETDEWEB)
Vournas, C.D. [National Technical Univ., Athens (Greece). Electrical Energy Systems Lab.
1995-08-01
This paper presents a voltage stability index (VSI) and a voltage controllability index (VCI), related to the eigenvalues of mxm matrices in a multimachine power system made up of m synchronous generators and a number of infinite buses. System loads can have an arbitrary voltage sensitivity described by generalized voltage exponents. These nonlinear loads are linearized around an operating point and incorporated into a modified admittance matrix, which is subsequently reduced to the generator terminals using an efficient algorithm and sparsity techniques. The indices proposed are tested in a practical system and it is demonstrated that they provide a timely warning during a sequence of events leading to voltage collapse.
Vibrations and Stability: Solved Problems
DEFF Research Database (Denmark)
Thomsen, Jon Juel
Worked out solutions for exercise problems in J. J. Thomsen 'Vibrations and Stability: Advanced Theory, Analysis, and Tools', Springer, Berlin - Heidelberg, 2003.......Worked out solutions for exercise problems in J. J. Thomsen 'Vibrations and Stability: Advanced Theory, Analysis, and Tools', Springer, Berlin - Heidelberg, 2003....
Voltage stability analysis in the new deregulated environment
Zhu, Tong
Nowadays, a significant portion of the power industry is under deregulation. Under this new circumstance, network security analysis is more critical and more difficult. One of the most important issues in network security analysis is voltage stability analysis. Due to the expected higher utilization of equipment induced by competition in a power market that covers bigger power systems, this issue is increasingly acute after deregulation. In this dissertation, some selected topics of voltage stability analysis are covered. In the first part, after a brief review of general concepts of continuation power flow (CPF), investigations on various matrix analysis techniques to improve the speed of CPF calculation for large systems are reported. Based on these improvements, a new CPF algorithm is proposed. This new method is then tested by an inter-area transaction in a large inter-connected power system. In the second part, the Arnoldi algorithm, the best method to find a few minimum singular values for a large sparse matrix, is introduced into the modal analysis for the first time. This new modal analysis is applied to the estimation of the point of voltage collapse and contingency evaluation in voltage security assessment. Simulations show that the new method is very efficient. In the third part, after transient voltage stability component models are investigated systematically, a novel system model for transient voltage stability analysis, which is a logical-algebraic-differential-difference equation (LADDE), is offered. As an example, TCSC (Thyristor controlled series capacitors) is addressed as a transient voltage stabilizing controller. After a TCSC transient voltage stability model is outlined, a new TCSC controller is proposed to enhance both fault related and load increasing related transient voltage stability. Its ability is proven by the simulation.
GRID VOLTAGE STABILITY ENHANCEMENT USING PHOTOVOLTAIC BASED STATIC SYNCHRONOUS COMPENSATOR
Directory of Open Access Journals (Sweden)
Arun Bhaskar Mayilvaganan
2013-01-01
Full Text Available Today, we are mostly dependent on non renewable energy that have been and will continue to be a major cause of pollution and other environmental degradation. Because of these problems and our dwindling supply of petroleum, finding sustainable alternatives is becoming increasingly urgent. Perhaps, the greatest challenge is in devising a sustainable future, which relies on integration and control of renewable energy sources in grid distributed generation. This study presents the usage of utilizing Photovoltaic (PV Solar Farm (SF during idle conditions as Static Synchronous Compensator (STATCOM, to regulate the point of common coupling voltage when the wind farm supply the power to the grid. The proposed control will enable increased connections of WECS to the grid. MATLAB/Simulink based simulation results are presented for validation of the system. The PV-STATCOM increase the stability of the grid with interconnected wind farm system without any use of additional compensator.
Wind Power Impact to Transient and Voltage Stability of the Power System in Eastern Denmark
DEFF Research Database (Denmark)
Rasmussen, Joana; Jørgensen, Preben; Palsson, Magni Thor
2005-01-01
Voltage stability, transient stability and reactive power compensation are extremely important issues for largescale integration of wind power in areas distant from the main transmission system in Eastern Denmark. This paper describes the application of a dynamic wind farm model in simulation...... studies for assessments of a large wind power penetration. The simulation results reveal problems with voltage stability due to the characteristic of wind turbine generation as well as the inability of the power system to meet the reactive power demand. Furthermore, the established model is applied...... to analyse challenges in system protection as means to reduce the risk of widespread blackouts....
Application of Cat Swarm Optimization in testing Static Load Models for Voltage Stability
Directory of Open Access Journals (Sweden)
G. Naveen Kumar
2016-03-01
Full Text Available Power System Load Modeling is a method which is used to model the power system and essential for voltage stability studies. Voltage stability defines the ability of a power network to maintain steady state voltages at all the buses under normal operating conditions, and when subjected to a disturbance. The research presented as part of this paper, deals with analysis of different static load models for voltage stability studies. The precision of the results are directly related to the load models used in this analysis. The method is analyzed using continuation power flow routine. Flexible AC Transmission System technology with a combination of Cat Swarm Optimization Meta Heuristic Search approach is applied to give a solution for the problem of instability. The effectiveness of the proposed method is demonstrated through quantitative simulation on standard IEEE 14 bus system for contingency condition.
Albatsh, Fadi M; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M A
2015-01-01
This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches.
Directory of Open Access Journals (Sweden)
Fadi M Albatsh
Full Text Available This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs including the line stability index (LQP, the voltage collapse proximity indicator (VCPI, and the line stability index (Lmn are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO and differential evolution (DE, which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches.
Albatsh, Fadi M.; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M. A.
2015-01-01
This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches. PMID:25874560
On-Line Voltage Stability Assessment based on PMU Measurements
DEFF Research Database (Denmark)
Garcia-Valle, Rodrigo; P. Da Silva, Luiz C.; Nielsen, Arne Hejde
2009-01-01
through statistic analysis. During the off-line analysis, a memory of high-risk situations following a pre-defined voltage stability criterion is obtained. Thereafter, basic statistics analyses are applied resulting in the definition of voltage regions. During on-line operation, voltage magnitudes......This paper presents a method for on-line monitoring of risk voltage collapse based on synchronised phasor measurement. As there is no room for intensive computation and analysis in real-time, the method is based on the combination of off-line computation and on-line monitoring, which are correlated...... of critical buses obtained by phasor measurements are monitored in relation to the risk regions. Comprehensive studies demonstrate that the proposed method could assist operators to avoid voltage collapse events, by taking preventive or emergency actions....
Optical voltage sensors: principle, problem and research proposal
Li, Changsheng
2016-10-01
Sensing principles and main problems to be solved for optical voltage sensors are briefly reviewed. Optical effects used for voltage sensing usually include electro-optic Pockels and Kerr effects, electro-gyration effect, elasto-optical effect, and electroluminescent effects, etc. In principle, typical optical voltage sensor is based on electro-optic Pockels crystals and closed-loop signal detection scheme. Main problems to be solved for optical voltage sensors include: how to remove influence of unwanted multiple optical effects on voltage sensing performance; how to select or develop a proper voltage sensing material and element; how to keep optical phase bias to be stable under temperature fluctuation and vibration; how to achieve dc voltage sensing, etc. In order to suppress the influence of unwanted optical effects and light beam coupling-related loss on voltage sensing signals, we may pay more attention to all-fiber and waveguide voltage sensors. Voltage sensors based on electroluminescent effects are also promising in some application fields due to their compact configuration, low cost and potential long-term reliability.
A study on threshold voltage stability of low operating voltage organic thin-film transistors
Padma, N.; Sen, Shaswati; Sawant, Shilpa N.; Tokas, R.
2013-08-01
A low operating voltage (<2 V) organic field-effect transistor (OFET) using phenylhexyltrichlorosilane (PTS) self-assembled monolayer (SAM) dielectric and copper phthalocyanine (CuPc) as semiconductor with improved mobility (0.035 cm2 V-1 s-1) and threshold voltage stability was demonstrated. This device showed better performance when compared to an OFET with octyltrichlorosilane (OTS-8) SAM dielectric. The improved mobility was attributed to the 2D growth mode of CuPc on PTS SAM because of surface energy matching between the two, whereas CuPc film on OTS-8 showed a 3D growth mode with larger grain boundary density. The higher threshold voltage stability of OFETs on PTS SAM was attributed to the efficient coverage and screening of trap centres at dielectric/semiconductor interface due to stronger intermolecular linking and formation of closely packed surface by the bulky phenyl end groups. Decrease in grain boundaries offered by 2D growth of CuPc for electron and hole trapping was also found to be another reason for improved threshold voltage stability. The results indicated that the nature of the end group of SAM dielectric, surface chemistry of dielectric and initial growth mode of semiconductors are all responsible for improvement in threshold voltage stability and enhanced performance of OFET.
Directory of Open Access Journals (Sweden)
Hugo Morais
2016-01-01
Full Text Available The need for developing new methodologies in order to improve power system stability has increased due to the recent growth of distributed energy resources. In this paper, the inclusion of a voltage stability index in distributed energy resources scheduling is proposed. Two techniques were used to evaluate the resulting multiobjective optimization problem: the sum-weighted Pareto front and an adapted goal programming methodology. With this new methodology, the system operators can consider both the costs and voltage stability. Priority can be assigned to one objective function according to the operating scenario. Additionally, it is possible to evaluate the impact of the distributed generation and the electric vehicles in the management of voltage stability in the future electric networks. One detailed case study considering a distribution network with high penetration of distributed energy resources is presented to analyse the proposed methodology. Additionally, the methodology is tested in a real distribution network.
Stability of DC Voltage Droop Controllers in VSC HVDC Systems
DEFF Research Database (Denmark)
Thams, Florian; Suul, Jon Are; D’Arco, Salvatore;
2015-01-01
Future multi-terminal HVDC systems are expected to utilize dc voltage droop controllers and several control implementations have been proposed in literature. This paper first classifies possible dc droop implementations in a simple framework. Then, the small-signal stability of a VSC-based conver......Future multi-terminal HVDC systems are expected to utilize dc voltage droop controllers and several control implementations have been proposed in literature. This paper first classifies possible dc droop implementations in a simple framework. Then, the small-signal stability of a VSC...
Temperature Stabilized Characterization of High Voltage Power Supplies
Krarup, Ole
2017-01-01
High precision measurements of the masses of nuclear ions in the ISOLTRAP experiment relies on an MR-ToF. A major source of noise and drift is the instability of the high voltage power supplies employed. Electrical noise and temperature changes can broaden peaks in time-of-flight spectra and shift the position of peaks between runs. In this report we investigate how the noise and drift of high-voltage power supplies can be characterized. Results indicate that analog power supplies generally have better relative stability than digitally controlled ones, and that the high temperature coefficients of all power supplies merit efforts to stabilize them.
Directory of Open Access Journals (Sweden)
J.Jithendranath
2013-07-01
Full Text Available This paper presents an evolutionary based algorithm for solving optimal reactive power dispatch problem in power system. The problem was designed as a Multi-Objective case with loss minimization and voltage stability as objectives. Generator terminal voltages, tap setting of transformers and reactive power generation of capacitor banks were taken as optimization variables. Modal analysis method is adopted to assess the voltage stability of system. The above presented problem was solved on basis of efficient and reliable technique among all evolutionary based algorithms, the Differential Evolution Technique. The proposed method has been tested on IEEE 30 bus system where the obtained results were found satisfactorily to a large extent that of reported earlier.
Strategies for Voltage Control and Transient Stability Assessment
Energy Technology Data Exchange (ETDEWEB)
Hiskens, Ian A.
2013-09-25
As wind generation grows, its influence on power system performance will becoming increasingly noticeable. Wind generation di ffers from traditional forms of generation in numerous ways though, motivating the need to reconsider the usual approaches to power system assessment and performance enhancement. The project has investigated the impact of wind generation on transient stability and voltage control, identifying and addressing issues at three distinct levels of the power system: 1) at the device level, the physical characteristics of wind turbine generators (WTGs) are quite unlike those of synchronous machines, 2) at the wind-farm level, the provision of reactive support is achieved through coordination of numerous dissimilar devices, rather than straightforward generator control, and 3) from a systems perspective, the location of wind-farms on the sub-transmission network, coupled with the variability inherent in their power output, can cause complex voltage control issues. The project has sought to develop a thorough understanding of the dynamic behaviour of type-3 WTGs, and in particular the WECC generic model. The behaviour of such models is governed by interactions between the continuous dynamics of state variables and discrete events associated with limits. It was shown that these interactions can be quite complex, and may lead to switching deadlock that prevents continuation of the trajectory. Switching hysteresis was proposed for eliminating deadlock situations. Various type-3 WTG models include control blocks that duplicate integrators. It was shown that this leads to non-uniqueness in the conditions governing steady-state, and may result in pre- and post-disturbance equilibria not coinciding. It also gives rise to a zero eigenvalue in the linearized WTG model. In order to eliminate the anomalous behaviour revealed through this investigation, WECC has now released a new generic model for type-3 WTGs. Wind-farms typically incorporate a variety of
Application of SMES in wind farm to improve voltage stability
Shi, J.; Tang, Y. J.; Ren, L.; Li, J. D.; Chen, S. J.
2008-09-01
For the wind farms introducing doubly fed induction generators (DFIGs), voltage stability is an essential issue which influences their widely integration into the power grid. This paper proposes the application of superconducting magnetic energy storage (SMES) in the power system integrated with wind farms. SMES can control the active and reactive power flow, realizing the operation in four quadrants independently. The introducing of SMES can smooth the output power flow of the wind farms, and supply dynamic voltage support. Using MATLAB/SIMULINK, the models of the DFIG, the power grid connected and the SMES are created. Simulation results show that the voltage stability of the power system integrated with wind farms can be improved considerably.
Stability Boundaries for Offshore Wind Park Distributed Voltage Control
DEFF Research Database (Denmark)
Gryning, Mikkel P.S.; Wu, Qiuwei; Kocewiak, Lukasz
2017-01-01
pilot control. Using data from the actual wind power plant, all stabilizing subsystem voltage proportional-integral controller parameters are first characterized based on their Hurwitz signature. Inner loop current control is then designed using Internal Mode Control principles, and guidelines for feed...
Voltage stability analysis of grid-connected wind farms with FACTS: Static and dynamic analysis
Directory of Open Access Journals (Sweden)
Kevin Zibran Heetun
2016-01-01
Full Text Available Recently, analysis of some major blackouts and failures of power system shows that voltage instability problem has been one of the main reasons of these disturbances and network collapses. In this article, a systematic approach to voltage stability analysis using various techniques for the IEEE 14-bus case study is presented. Static analysis is used to analyze the voltage stability of the system under study, while the dynamic analysis is used to evaluate the performance of compensators. The static techniques used are power flow, V–P curve analysis, and Q–V modal analysis. In this study, Flexible Alternating Current Transmission system (FACTS devices—namely, static synchronous compensators (STATCOMs and static var compensators (SVCs—are used as reactive power compensators, taking into account maintaining the violated voltage magnitudes of the weak buses within the acceptable limits defined in ANSI C84.1. Simulation results validate that both the STATCOMs and the SVCs can be effectively used to enhance the static voltage stability and increasing network loadability margin. Additionally, based on the dynamic analysis results, it has been shown that STATCOMs have superior performance, in dynamic voltage stability enhancement, compared to SVCs.
Directory of Open Access Journals (Sweden)
V. Tamilselvan
2015-05-01
Full Text Available This study addresses a shuffled frog leaping algorithm for solving the multi-objective reactive power dispatch problem in a power system. Optimal Reactive Power Dispatch (ORPD is formulated as a nonlinear, multi-modal and mixed-variable problem. The intended technique is based on the minimization of the real power loss, minimization of voltage deviation and maximization of the voltage stability margin. Generator voltages, capacitor banks and tap positions of tap changing transformers are used as optimization variables of this problem. A memetic meta-heuristic named as shuffled frog-leaping algorithm is intended to solve multi-objective optimal reactive power dispatch problems considering voltage stability margin and voltage deviation. The Shuffled Frog-Leaping Algorithm (SFLA is a population-based cooperative search metaphor inspired by natural memetics. The algorithm contains elements of local search and global information exchange. The most important benefit of this algorithm is higher speed of convergence to a better solution. The intended method is applied to ORPD problem on IEEE 57 bus power systems and compared with two versions of differential evolutionary algorithm. The simulation results show the effectiveness of the intended method.
Directory of Open Access Journals (Sweden)
R. Kalaivani
2012-01-01
Full Text Available Problem statement: Voltage instability and voltage collapse have been considered as a major threat to present power system networks due to their stressed operation. It is very important to do the power system analysis with respect to voltage stability. Approach: Flexible AC Transmission System (FACTS is an alternating current transmission system incorporating power electronic-based and other static controllers to enhance controllability and increase power transfer capability. A FACTS device in a power system improves the voltage stability, reduces the power loss and also improves the load ability of the system. Results: This study investigates the application of Particle Swarm Optimization (PSO and Genetic Algorithm (GA to find optimal location and rated value of Static Var Compensator (SVC device to minimize the voltage stability index, total power loss, load voltage deviation, cost of generation and cost of FACTS devices to improve voltage stability in the power system. Optimal location and rated value of SVC device have been found in different loading scenario (115%, 125% and 150% of normal loading using PSO and GA. Conclusion/Recommendations: It is observed from the results that the voltage stability margin is improved, the voltage profile of the power system is increased, load voltage deviation is reduced and real power losses also reduced by optimally locating SVC device in the power system. The proposed algorithm is verified with the IEEE 14 bus, IEEE 30 bus and IEEE 57 bus.
The effect of reactive power generation modeling on voltage stability analysis
Energy Technology Data Exchange (ETDEWEB)
Tovar, E.; Guizar, J.G.C. [Inst. de Investigaciones Electricas, Cuernavaca, Morelos (Mexico)
2010-08-13
One of the most significant concerns for power system planning and operation in many countries involves problems related to voltage instability in electrical power systems. Blackouts have been caused by voltage instability problems throughout the world during the last few decades. Several factors can contribute to long term voltage instability problems, including high active and reactive loading, operation of on load tap changer transformers, inadequate locally available reactive power resources, load characteristics at low voltage magnitudes and operation of relay protection. There is a significant need to evaluate an index which gives the operating point proximity to voltage instability. This paper examined the influence of generator voltage dependent reactive power production on system voltage stability using the minimum singular value from the Jacobian Matrix of the load flow formulation. The synchronous generator model considered voltage reactive power limits due to maximum armature current, maximum and minimum field current as well as under excitation limiters. The generation model used in this paper was included in an ordinary load flow program, and resulted from studies of a representative 62 bus Norwest control area Mexican system, which included 19 generators. Specifically, the paper discussed the generator model with particular reference to the maximum field current limit; armature current limit; minimum field current limit; and underexcitation limit. The singular value decomposition and computational results were also presented. It was concluded that as the loading of the system increases, the reactive power produced by the machines also increases, and that reactive power is delivered when the induced voltage is greater than the terminal voltage. 15 refs., 3 tabs., 2 figs.
Voltage Stability of Long Transmission Line Equipped with a Thyristor Controlled Series Capacitor
Directory of Open Access Journals (Sweden)
Prechanon Kumkratug
2012-01-01
Full Text Available Problem statement: Power-Voltage curve provides very important information for voltage stability analysis. The exact long transmission line model consists of the resistance and the reactance. The resistance causes in the active line loss. It is not easy task to achieve the power-voltage curve characteristics of power system with the exact long line model equipeed with a Thyristor Controlled Series Capacitor (TCSC. Approach: This study applies the concept of the Newton-Raphson method to iteratively solve the nonlinear power flow equations. The Power-Voltage (P-V curve charateristic of the system without line loss and with line loss are plotted and compared on various cases. Results: It is found from the study that the resistance of the line obviously provides the negative effects on the voltage stability. The line loss causes in the decrement of the critical point. In addition, it is found that the leading power factor can increase the critical point of P-V curve. Conclusion: The exact long line model should be considered for voltage stability analysis of the system with the long transmission line.
Voltage Stability of Medium Transmission Line Equipped with a Thyristor Controlled Series Capacitor
Directory of Open Access Journals (Sweden)
Prechanon Kumkratug
2012-01-01
Full Text Available Problem statement: Power-Voltage curve provides very important information for voltage stability analysis. The exact medium transmission line model consists of the resistance and the reactance. The resistance causes in the active line loss. It is not an easy task to achieve the power-voltage curve characteristics of power system with the exact medium line model equipped with a. Thyristor Controlled Series Capacitor (TCSC. Approach: This study applies the concept of the Newton-Raphson method to iteratively solve the nonlinear power flow equations. The Power-Voltage (P-V curve characteristic of the system without line loss and with line loss are plotted and compared with various cases. Results: It is found from the study that the resistance of the line obviously provides the negative effects on the voltage stability. The line loss causes in the decrement of the critical point. In addition, it is found that the leading power factor can increase the critical point of P-V curve. Conclusion: The exact medium line model should be considered for voltage stability analysis of the system with the medium transmission line.
Local Dynamic Reactive Power for Correction of System Voltage Problems
Energy Technology Data Exchange (ETDEWEB)
Kueck, John D [ORNL; Rizy, D Tom [ORNL; Li, Fangxing [ORNL; Xu, Yan [ORNL; Li, Huijuan [University of Tennessee, Knoxville (UTK); Adhikari, Sarina [ORNL; Irminger, Philip [ORNL
2008-12-01
Distribution systems are experiencing outages due to a phenomenon known as local voltage collapse. Local voltage collapse is occurring in part because modern air conditioner compressor motors are much more susceptible to stalling during a voltage dip than older motors. These motors can stall in less than 3 cycles (.05s) when a fault, such as on the sub-transmission system, causes voltage to sag to 70 to 60%. The reasons for this susceptibility are discussed in the report. During the local voltage collapse, voltages are depressed for a period of perhaps one or two minutes. There is a concern that these local events are interacting together over larger areas and may present a challenge to system reliability. An effective method of preventing local voltage collapse is the use of voltage regulation from Distributed Energy Resources (DER) that can supply or absorb reactive power. DER, when properly controlled, can provide a rapid correction to voltage dips and prevent motor stall. This report discusses the phenomenon and causes of local voltage collapse as well as the control methodology we have developed to counter voltage sag. The problem is growing because of the use of low inertia, high efficiency air conditioner (A/C) compressor motors and because the use of electric A/C is growing in use and becoming a larger percentage of system load. A method for local dynamic voltage regulation is discussed which uses reactive power injection or absorption from local DER. This method is independent, rapid, and will not interfere with conventional utility system voltage control. The results of simulations of this method are provided. The method has also been tested at the ORNL s Distributed Energy Communications and Control (DECC) Laboratory using our research inverter and synchronous condenser. These systems at the DECC Lab are interconnected to an actual distribution system, the ORNL distribution system, which is fed from TVA s 161kV sub-transmission backbone. The test results
Stability Boundaries for Offshore Wind Park Distributed Voltage Control
DEFF Research Database (Denmark)
Gryning, Mikkel P.S.; Wu, Qiuwei; Kocewiak, Lukasz;
2016-01-01
In order to identify mechanisms causing slow reactive power oscillations observed in an existing offshore wind power plant, and be able to avoid similar events in the future, voltage control is studied in this paper for a plant with a static synchronous compensator, type-4 wind turbines and a park...... pilot control. Using data from the actual wind power plant, all stabilizing subsystem voltage proportional-integral controller parameters are first characterized based on their Hurwitz signature. Inner loop current control is then designed using Internal Mode Control principles, and guidelines for feed...... forward filter design are given to obtain required disturbance rejection properties. The paper contributes by providing analytical relations between power plant control, droop, sampling time, electrical parameters and voltage control characteristics, and by assessing frequencies and damping of reactive...
Fast and accurate method for computing ATC with voltage stability
Eidiani, M; Vahedi, E
2002-01-01
Order 889 mandated each control area to computer ATC (Available Transfer Capability) and post them on a communication system called the Open Access Same-time Information System (OASIS). Approaches of computing ATC can be divided into the following groups: Static and Dynamic methods. This paper presents a fast method for ATC calculations with voltage stability termination criteria. We use estimation of the determinant of Jacobian matrix for assessment of voltage stability. This method is compared with these methods: different between energy in SEP (Stable Equilibrium Point) and UEP (Unstable Equilibrium Point), ts index of Dr.Chiang and continuation power flow. The idea are demonstrated on 2, 3, 7 (CIGRE), 10, 30 (IEEE) and 145 bus (Iowa State University).
Multigrid method for stability problems
Taasan, Shlomo
1988-01-01
The problem of calculating the stability of steady state solutions of differential equations is treated. Leading eigenvalues (i.e., having maximal real part) of large matrices that arise from discretization are to be calculated. An efficient multigrid method for solving these problems is presented. The method begins by obtaining an initial approximation for the dominant subspace on a coarse level using a damped Jacobi relaxation. This proceeds until enough accuracy for the dominant subspace has been obtained. The resulting grid functions are then used as an initial approximation for appropriate eigenvalue problems. These problems are being solved first on coarse levels, followed by refinement until a desired accuracy for the eigenvalues has been achieved. The method employs local relaxation on all levels together with a global change on the coarsest level only, which is designed to separate the different eigenfunctions as well as to update their corresponding eigenvalues. Coarsening is done using the FAS formulation in a non-standard way in which the right hand side of the coarse grid equations involves unknown parameters to be solved for on the coarse grid. This in particular leads to a new multigrid method for calculating the eigenvalues of symmetric problems. Numerical experiments with a model problem demonstrate the effectiveness of the method proposed. Using an FMG algorithm a solution to the level of discretization errors is obtained in just a few work units (less than 10), where a work unit is the work involved in one Jacobi relization on the finest level.
Tools for voltage stability analysis, including a probabilistic approach
Energy Technology Data Exchange (ETDEWEB)
Vieira Filho, X.; Martins, N.; Bianco, A.; Pinto, H.J.C.P. [Centro de Pesquisas de Energia Eletrica (CEPEL), Rio de Janeiro, RJ (Brazil); Pereira, M.V.F. [Power System Research (PSR), Inc., Rio de Janeiro, RJ (Brazil); Gomes, P.; Santos, M.G. dos [ELETROBRAS, Rio de Janeiro, RJ (Brazil)
1994-12-31
This paper reviews some voltage stability analysis tools that are being used or envisioned for expansion and operational planning studies in the Brazilian system, as well as, their applications. The paper also shows that deterministic tools can be linked together in a probabilistic framework, so as to provide complementary help to the analyst in choosing the most adequate operation strategies, or the best planning solutions for a given system. (author) 43 refs., 8 figs., 8 tabs.
Alemadi, Nasser Ahmed
Deregulation has brought opportunities for increasing efficiency of production and delivery and reduced costs to customers. Deregulation has also bought great challenges to provide the reliability and security customers have come to expect and demand from the electrical delivery system. One of the challenges in the deregulated power system is voltage instability. Voltage instability has become the principal constraint on power system operation for many utilities. Voltage instability is a unique problem because it can produce an uncontrollable, cascading instability that results in blackout for a large region or an entire country. In this work we define a system of advanced analytical methods and tools for secure and efficient operation of the power system in the deregulated environment. The work consists of two modules; (a) contingency selection module and (b) a Security Constrained Optimization module. The contingency selection module to be used for voltage instability is the Voltage Stability Security Assessment and Diagnosis (VSSAD). VSSAD shows that each voltage control area and its reactive reserve basin describe a subsystem or agent that has a unique voltage instability problem. VSSAD identifies each such agent. VS SAD is to assess proximity to voltage instability for each agent and rank voltage instability agents for each contingency simulated. Contingency selection and ranking for each agent is also performed. Diagnosis of where, why, when, and what can be done to cure voltage instability for each equipment outage and transaction change combination that has no load flow solution is also performed. A security constrained optimization module developed solves a minimum control solvability problem. A minimum control solvability problem obtains the reactive reserves through action of voltage control devices that VSSAD determines are needed in each agent to obtain solution of the load flow. VSSAD makes a physically impossible recommendation of adding reactive
Stability problem in Rindler spacetime
Institute of Scientific and Technical Information of China (English)
2007-01-01
The stability problem of the Rindler spacetime is carefully studies by using the scalar wave perturbation. Using two different coordinate systems, the scalar wave equation is investigated. The results are different in the two cases.They are analysed and compared with each other in detail. The following conclusions are obtained: (a) the Rindler spacetime as a whole is not stable; (b) the Rindler spacetime can exist stably only as part of the Minkowski spacetime,and the Minkowski spacetime can be a real entity independently; (c) there are some defects for the scalar wave equation written by the Rindler coordinates, and it is unsuitable for the investigation of the stability properties of the Rindler spacetime. All these results may shed some light on the stability properties of the Schwarzschild black hole. It is natural and reasonable for one to infer that: (a) perhaps the Regge-Wheeler equation is not sufficient to determine the stable properties; (b) the Schwarzschild black hole as a whole might be really unstable; (c) the Kruskal spacetime is stable and can exist as a real physical entity; whereas the Schwarzschild black hole can occur only as part of the Kruskal spacetime.
Robust Frequency and Voltage Stability Control Strategy for Standalone AC/DC Hybrid Microgrid
Directory of Open Access Journals (Sweden)
Furqan Asghar
2017-05-01
Full Text Available The microgrid (MG concept is attracting considerable attention as a solution to energy deficiencies, especially in remote areas, but the intermittent nature of renewable sources and varying loads cause many control problems and thereby affect the quality of power within a microgrid operating in standalone mode. This might cause large frequency and voltage deviations in the system due to unpredictable output power fluctuations. Furthermore, without any main grid support, it is more complex to control and manage the system. In past, droop control and various other coordination control strategies have been presented to stabilize the microgrid frequency and voltages, but in order to utilize the available resources up to their maximum capacity in a positive way, new and robust control mechanisms are required. In this paper, a standalone microgrid is presented, which integrates renewable energy-based distributed generations and local loads. A fuzzy logic-based intelligent control technique is proposed to maintain the frequency and DC (direct current-link voltage stability for sudden changes in load or generation power. Also from a frequency control perspective, a battery energy storage system (BESS is suggested as a replacement for a synchronous generator to stabilize the nominal system frequency as a synchronous generator is unable to operate at its maximum efficiency while being controlled for stabilization purposes. Likewise, a super capacitor (SC and BESS is used to stabilize DC bus voltages even though maximum possible energy is being extracted from renewable generated sources using maximum power point tracking. This newly proposed control method proves to be effective by reducing transient time, minimizing the frequency deviations, maintaining voltages even though maximum power point tracking is working and preventing generators from exceeding their power ratings during disturbances. However, due to the BESS limited capacity, load switching
Stability Analysis and Controller Synthesis for Single-Loop Voltage-Controlled VSIs
DEFF Research Database (Denmark)
Wang, Xiongfei; Loh, Poh Chiang; Blaabjerg, Frede
2017-01-01
This paper analyzes the stability of the digital single-loop voltage-controlled Voltage-Source Inverters (VSIs) using linear voltage regulators. It reveals that the phase lags caused by using the resonant controller and the time delay of digital control system can stabilize the voltage loop without...... damping of the LC-filter resonance. The stability region for the digital single-loop resonant voltage control is then identified considering the effects of the discretization methods applied to the resonant controller. An enhanced voltage control scheme with widened stability region is subsequently...
Directory of Open Access Journals (Sweden)
P. Balachennaiah
2016-06-01
Full Text Available This paper proposes a Firefly algorithm based technique to optimize the control variables for simultaneous optimization of real power loss and voltage stability limit of the transmission system. Mathematically, this issue can be formulated as nonlinear equality and inequality constrained optimization problem with an objective function integrating both real power loss and voltage stability limit. Transformers taps, unified power flow controller and its parameters have been included as control variables in the problem formulation. The effectiveness of the proposed algorithm has been tested on New England 39-bus system. Simulation results obtained with the proposed algorithm are compared with the real coded genetic algorithm for single objective of real power loss minimization and multi-objective of real power loss minimization and voltage stability limit maximization. Also, a classical optimization method known as interior point successive linear programming technique is considered here to compare the results of firefly algorithm for single objective of real power loss minimization. Simulation results confirm the potentiality of the proposed algorithm in solving optimization problems.
A Sufficient Condition for Power Flow Insolvability with Applications to Voltage Stability Margins
Molzahn, Daniel K; DeMarco, Christopher L
2012-01-01
For the nonlinear power flow problem specified with standard PQ, PV, and slack bus equality constraints, we present a sufficient condition under which the specified set of nonlinear algebraic equations has no solution. This sufficient condition is constructed in a framework of an associated feasible, convex optimization problem. The objective employed in this optimization problem yields a measure of distance (in a parameter set) to the power flow solution boundary. In practical terms, this distance is closely related to quantities that previous authors have proposed as voltage stability margins. A typical margin is expressed in terms of the parameters of system loading (injected powers); here we additionally introduce a new margin in terms of the parameters of regulated bus voltages.
Stability Analysis and Controller Synthesis for Digital Single-Loop Voltage-Controlled Inverters
DEFF Research Database (Denmark)
Wang, Xiongfei; Loh, Poh Chiang; Blaabjerg, Frede
2016-01-01
This paper analyzes first the stability of single-loop digital voltage control scheme for the LC-filtered voltage source inverters. It turns out that the phase lag, caused by the time delay of digital control system and by the use of integral controller, can stabilize the voltage loop without...... damping of LC-filter resonance. The stability regions are then identified with alternative voltage controller synthesized. For further widening the stability region, an active damping approach is proposed and co-designed with the voltage controller in the discrete z-domain. Simulations and experimental...
Directory of Open Access Journals (Sweden)
K.MALARVIZHI
2010-06-01
Full Text Available Grid connected Fixed Speed Wind Turbines (FSWT may cause voltage stability problems which results in islanding of the generator from the grid. Voltage stability is a major issue to achieve the uninterrupted operation of wind farms equipped with FSWTs. In this paper the design of a Static Synchronous Compensator (STATCOM based on Cascaded H-Bridge (CHB – Multi Level Converter (MLC is proposed. The dynamic behavior of 3 level and 5 level CMC based STATCOM is validated by simulation with MATLAB/SIMULINK simulation techniques.A detailed analysis of the operating characteristics of the various inverter topologies are compared in the paper. To analyze the performance of the STATCOM connected in shunt with the transmission line, an induction generator based wind farm has been considered. The complete digital simulation of the STATCOM incorporated into the power system is performed in the MATLAB/SIMULINK environment and the results are presented to validate the feasibility of the proposed topology.
Stabilizing Ferroresonance Oscillations in Voltage Transformers Using Limiter Circuit
Directory of Open Access Journals (Sweden)
Hamid Radmanesh
2012-12-01
Full Text Available This paper employs the multiple scales method and chaos theory for analyzing chaotic behavior of the voltage transformer (VT with linear core loss model. It is shown that ferroresonance phenomenon in VTs can be classified as chaotic dynamics, including a sequence of bifurcations such as period doubling bifurcation (PDB, saddle node bifurcation (SNB, Hopf Bifurcation (HB and chaos. Bifurcation diagrams and phase plane diagrams are drawn using a continuation method for linear core loss model and lyapunov exponents are obtained using the multiple scales method. At first an overview of the subject in the literature is provided. Then, ferroresonance phenomenon is introduced and its various types in a VT are simulated. Finally the effects of ferroresonance suppression circuit on stabilizing these oscillations are studied. The proposed approach is implemented using MATLAB, and simulation results are presented. The results show connecting the ferroresonance suppression circuit to the system configuration, causes great controlling effect on ferroresonance overvoltage.
Directory of Open Access Journals (Sweden)
S. Sakthivel
2013-07-01
Full Text Available Modern power system networks are operated under highly stressed conditions and there is a risk of voltage instability problems owing to increased load demand. A power system needs to be with sufficient voltage stability margin for secured operation. In this study, SVC parameters of location and size along with generator bus voltages, transformer tap settings are considered as control parameters for voltage stability limit improvement by minimizing loss and voltage deviation. The control parameters are varied in a coordinated manner for better results. The line based LQP voltage stability indicator is used for voltage stability assessment. The nature inspired meta heuristic Big Bang-Big Crunch (BB-BC algorithm is exploited for optimization of the control variables and the performance is compared with that of PSO algorithm. The effectiveness of the proposed algorithm is tested on the standard IEEE 30 bus system under normal and N-1 line outage contingency conditions. The results obtained from the simulation encourage the performances of the new algorithm.
Assessment of the impact that individual voltage source has on a generator’s stability
DEFF Research Database (Denmark)
Dmitrova, Evgeniya; Jóhannsson, Hjörtur; Nielsen, Arne Hejde
2012-01-01
This paper presents an approach for splitting equivalent Thevenin voltage into components induced by each voltage source in the reduced grid. Thevenin equivalent representation of the system is sometimes used for stability assessment of a given generator, where the Thevenin voltage is one...... of the key variables affecting the stability conditions. Thevenin voltage is formed by components induced by each voltage source in the grid, while depending on topology and system parameters, the impact of these components on the equivalent Thevenin voltage Eth might vary considerably. This paper...
Understanding the unbalanced-voltage problem in wind turbine generation
Energy Technology Data Exchange (ETDEWEB)
Muljadi, E.; Butterfield, C.P.; Batan, T.; Yildirim, D.
2000-02-28
Most wind turbines are equipped with line-connected induction generators. Induction generators are very attractive as wind turbine generators due to their low cost, ruggedness and the need for little or no maintenance. At constant frequency, the induction generator operates in a small range of speeds and, therefore, it operated with a small range of slips with respect to synchronous speed. Compared to a synchronous generator, an induction generator provides lower stiffness, thus alleviating the mechanical stress. In a weak power system network, an unbalanced load at the distribution lines can cause unbalanced voltage conditions. If an induction generator is connected to an unbalanced voltage, the resulting stator current will be unbalanced. The unbalanced current creates unequal heating (hot spots) on the stator winding. The heat may increase the winding temperature, which degrades the insulation of the winding, i.e., the life expectancy of the winding. Unbalanced currents also create torque pulsation on the shaft resulting in audible noise and extra mechanical stress. This paper explores the unbalanced voltage problem in induction generators. The levels of unbalance and the loads are varied. Experimental and predicted results are presented in this paper.
Health problems from radiation of high-voltage facilities
Directory of Open Access Journals (Sweden)
Hossein Ali Yousefi Rizi
2013-01-01
Full Text Available Aims: The aim of this study was to survey the health problems caused by exposure to high-voltage facility radiation. Materials and Methods: Sampling included workers exposed to electromagnetic fields at high-voltage facilities. The strength of the electric and magnetic fields was determined by a field meter. A questionnaire was used to evaluate the prevalence of subjective and psychological symptoms. Statistical descriptive used and data analyzed by a Student′s t-tests. Results: This study indicates that increased symptoms among the exposed workers including depression, anxiety, hostility, paranoia, inter-sensitivity, and obsession-compulsion. Some of the self-reported symptoms were, headache (53.5%, fatigue (35.6%, difficulties in concentration (32.5%, vertigo/dizziness (30.4%, attention disorders (28.8%, nervousness (28.1%, and palpitations (14.7%. A significant relationship was observed between the exposure to the electromagnetic field and psychological symptoms (P < 0.05. Conclusion: Radiation of high-voltage facilities probably increased the risk of mental disorders and intensified them in susceptible workers, especially depression. This finding confirmed the results obtained in provocative studies that indicated an increase in the risk of psychological symptoms, which was put forth by several investigators Observation of occupational health and other control measures play an important role in decreasing the symptoms.
New online voltage stability margins and risk assessment for multi-bus smart power grids
Aldeen, M.; Saha, S.; Alpcan, T.; Evans, R. J.
2015-07-01
This paper presents a quantitative framework for assessment of voltage stability in smart power networks. First, new stability indices similar to gain and phase margins in linear time invariant control systems are introduced. These indices can be computed online in conjunction with load-flow calculations. Then, a novel risk assessment framework incorporating the new stability indices is developed to methodologically quantify the voltage stability risks a power system faces at any given operating condition. In contrast to existing local stability indices and qualitative risk approaches, the indices and framework introduced provide analytical and quantitative evaluation of voltage stability and associated risks. The results are illustrated with a numerical example.
Vibrations and Stability - Order & Chaos, Solved Problems
DEFF Research Database (Denmark)
Thomsen, Jon Juel
2002-01-01
A collection of worked out solutions to many of the exercise problems in my textbook "Vibrations and Stability", McGraw-Hill, London, 1997.......A collection of worked out solutions to many of the exercise problems in my textbook "Vibrations and Stability", McGraw-Hill, London, 1997....
Development of a terminal voltage stabilization system for the FOTIA at BARC
Indian Academy of Sciences (India)
M J Kansara; P Sapna; N B V Subrahmanyam; J P Bhatt; P Singh
2002-11-01
A terminal voltage stabilization system for the folded tandem ion accelerator (FOTIA) was developed and is in continuous use. The system achieves good voltage stabilization, eliminates ground loops and noise interference. It incorporates a correcting circuit for compensating the mains frequency variations in the GVM ampliﬁer circuit. The present system has two modes of operation namely GVM control mode and slit control mode. A voltage stability of about ± 2 kV has been achieved. In this paper, some of the salient features of the voltage stabilization system are discussed.
Boundary stabilization of transmission problems
Cardoso, Fernando; Vodev, Georgi
2010-02-01
We study the transmission problem in bounded domains with dissipative boundary conditions. Under some natural assumptions, we prove uniform bounds of the corresponding resolvents on the real axis at high frequency and, as a consequence, we obtain regions free of eigenvalue. To this end, we extend the result of Cardoso et al. ["Distribution of resonances and local energy decay in the transmission problem. II," Math. Res. Lett. 6, 377 (1999)] under more general assumptions. As an application, we get exponential decay of the energy of the solutions of the corresponding mixed boundary value problems.
Directory of Open Access Journals (Sweden)
TOMA R.
2016-09-01
Full Text Available The paper presents a comparative study between the effects on voltage stability of the integration of a wind farm into the electricity grid with or without voltage dependent loads in the context of different locations of a synchronous compensator from the grid. The P-V curves are built by using the PowerFactory DigSilent 15.2.2 and a DPL script that implements a simplified form of the Continuation Power Flow method.
Stability Analysis for Stochastic Optimization Problems
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Stochastic optimization offers a means of considering the objectives and constrains with stochastic parameters. However, it is generally difficult to solve the stochastic optimization problem by employing conventional methods for nonlinear programming when the number of random variables involved is very large. Neural network models and algorithms were applied to solve the stochastic optimization problem on the basis of the stability theory. Stability for stochastic programs was discussed. If random vector sequence converges to the random vector in the original problem in distribution, the optimal value of the corresponding approximation problems converges to the optimal value of the original stochastic optimization problem.
Directory of Open Access Journals (Sweden)
Khan Aafreen
2014-11-01
Full Text Available Power system security is recognized as one of the major problems in many power systems throughout the world. Power system insecurity such as transmission lines being overloaded causes transmission elements cascade outages, which may lead to complete blackout. In accordance with these reasons, the prediction and recognition of voltage instability in power system has particular importance and it makes the network security stronger. This work, by considering the power system contingencies based on the effects of them on Mega Watt Margin (MWM and maximum loading point (MLP is focused to analyse the voltage stability using continuation power flow method. The study has been carried out on IEEE 30-Bus Test System using MATLAB and PSAT softwares and results are presented.
Transient Voltage Stability Analysis and Improvement of A Network with different HVDC Systems
DEFF Research Database (Denmark)
Liu, Yan; Chen, Zhe
2011-01-01
the theoretical analysis and the improved control method, real time simulation model of a hybrid multi-infeed HVDC system based on western Danish power system is established in RTDS™. Simulation results show that the enhanced transient voltage stability can be achieved.......This paper presents transient voltage stability analysis of an AC system with multi-infeed HVDC links including a traditional LCC HVDC link and a VSC HVDC link. It is found that the voltage supporting capability of the VSC-HVDC link is significantly influenced by the tie-line distance between...... the two links and the size of loads. In order to improve the transient voltage stability, a voltage adjusting method is proposed in this paper. A voltage increment component has been introduced into the outer voltage control loop under emergency situation caused by severe grid faults. In order to verify...
Effect of semiconductor-controlled voltage injection by UPFC and ULTC on power system stability
Alavian Mehr, Alireza
Commercial availability of various power semiconductor switches indicates proliferation of power electronic based apparatus in utility power systems. Furthermore, existing power system apparatus, e.g. mechanical phase shifters and mechanical tap changing transformers, will be retrofitted to utilize higher switching speed of semiconductor switches. A group of these apparatus, i.e., unified power flow controller (UPFC), static phase shifter (SPS), under-load tap-changing (ULTC) transformer and static series capacitor (SSC), perform their respective functions by means of injecting series controlled voltages in power systems. This thesis demonstrates that fast series voltage injection, for dynamic power flow regulation, can result in voltage dynamics and even voltage instability. This indicates that fast voltage injection by means of power electronic based apparatus can couple voltage stability and angle stability phenomena. To investigate this coupling phenomena, the voltage dependency of the load must be adequately represented in the load model. The reported studies in this work are based on representing the load by a combination of static and dynamic loads. This thesis primarily investigates impacts of UPFC and semiconductor-controlled ULTC on voltage stability and angle stability phenomena. An eigen analysis approach is used for the studies. The eigen analysis results are validated by digital time-domain simulations using a transient stability software. Both the eigen analysis and the transient stability software tools are tailored to account for angle and voltage stability phenomena.
A new application area for fullerenes: voltage stabilizers for power cable insulation.
Jarvid, Markus; Johansson, Anette; Kroon, Renee; Bjuggren, Jonas M; Wutzel, Harald; Englund, Villgot; Gubanski, Stanislaw; Andersson, Mats R; Müller, Christian
2015-02-01
Fullerenes are shown to be efficient voltage-stabilizers for polyethylene, i.e., additives that increase the dielectric strength of the insulation material. Such compounds are highly sought-after because their use in power-cable insulation may considerably enhance the transmission efficiency of tomorrow's power grids. On a molal basis, fullerenes are the most efficient voltage stabilizers reported to date.
Steady-state analysis of the effect of reactive generation limits in voltage stability
Energy Technology Data Exchange (ETDEWEB)
Echavarren, F.M.; Lobato, E.; Rouco, L. [School of Engineering of Universidad Pontificia Comillas, C/Alberto Aguilera, 23, 28015 Madrid (Spain)
2009-09-15
Voltage collapse phenomena are highly affected by reactive power generation limits. Saturation of the reactive power generation limits of a unit may result in a deterioration of the voltage stability. However, in some cases when the power network is operating close to the voltage collapse point, the reactive power generation saturation of a unit can change the system voltages immediately from stable to unstable; thus, a dynamic voltage collapse leading to blackout may follow. This paper presents a steady-state analysis of the immediate instability caused by reactive power generation saturation phenomena. For this purpose, the paper proposes a novel index that evaluates ''when'' and ''why'' a reactive power generation saturation will only result in a deterioration of the system voltage stability or, on the contrary, it will make the system voltages immediately unstable. (author)
Power flow control and voltage stability limit: regulating transformer versus UPFC
Energy Technology Data Exchange (ETDEWEB)
Haque, M.H. [Nanyang Technological Univ., Center for Advanced Power Electronics, Nanyang (Singapore)
2004-05-01
Power flow through an AC transmission line can be controlled by injecting an adjustable compensating voltage in series with the line. This paper evaluates and compares the power flow control ranges of a simple system obtained by injecting an adjustable series compensating voltage produced by a regulating transformer and unified power flow controller. The static voltage stability limits of the system with a regulating transformer and unified power flow controller are also determined and compared. In evaluating the power flow control ranges and voltage stability limits, the transmission line of the system is modelled in four different ways. The results obtained for various line models are also compared. (Author)
Voltage stability issues for a benchmark grid model including large scale wind power
DEFF Research Database (Denmark)
Eek, Jarle; Lund, Torsten; Di Marzio, Guiseppe
2006-01-01
The objective of the paper is to investigate how the voltage stability of a relatively weak network after a grid fault is affected by the connection of a large wind park. A theoretical discussion of the stationary and dynamic characteristics of the Short Circuit Induction Generator and the Doubly...... of the network and saturation of the external reactive power compensation units provides a good basis for evaluation of the voltage stability. For the DFIG it is concluded that the speed stability limit is mainly determined by the voltage limitation of the rotor converter...
Xu, Yan; Zhang, Rui; Zhao, Junhua; Dong, Zhao Yang; Wang, Dianhui; Yang, Hongming; Wong, Kit Po
2016-08-01
In the smart grid paradigm, growing integration of large-scale intermittent renewable energies has introduced significant uncertainties to the operations of an electric power system. This makes real-time dynamic security assessment (DSA) a necessity to enable enhanced situational-awareness against the risk of blackouts. Conventional DSA methods are mainly based on the time-domain simulation, which are insufficiently fast and knowledge-poor. In recent years, the intelligent system (IS) strategy has been identified as a promising approach to facilitate real-time DSA. While previous works mainly concentrate on the rotor angle stability, this paper focuses on another yet increasingly important dynamic insecurity phenomenon-the short-term voltage instability, which involves fast and complex load dynamics. The problem is modeled as a classification subproblem for transient voltage collapse and a prediction subproblem for unacceptable dynamic voltage deviation. A hierarchical IS is developed to address the two subproblems sequentially. The IS is based on ensemble learning of random-weights neural networks and is implemented in an offline training, a real-time application, and an online updating pattern. The simulation results on the New England 39-bus system verify its superiority in both learning speed and accuracy over some state-of-the-art learning algorithms.
Directory of Open Access Journals (Sweden)
R.KALAIVANI
2016-10-01
Full Text Available Due to huge increase in power demand, power system network will lead to major problems such as voltage instability and voltage collapse in the power system. To overcome these problems, Flexible AC Transmission System (FACTS devices have been implemented in power system. By placing these devices in suitable locations, the power system can be operated far away from the instability point. In this paper, the optimal location and the ratings of FACTS devices such as Thyristor Controlled Series Capacitor (TCSC, Static VAR Compensator (SVC and Unified Power Flow Controller (UPFC are determined using Genetic Algorithm (GA. A multi objective optimization problem is formulated with the consideration of minimizing voltage stability index, real power loss and generator cost. Evolutionary algorithm such as GA is a population based search method is used for solving multi objective optimization problem that is capable of searching for multiple solutions concurrently in a single run and provide an optimal solution. It is observed from the results that the voltages stability index, real power loss and generator cost are reduced by optimally locating the FACTS devices in the power system. IEEE 14 bus and IEEE 57 bus systems are used to demonstrate the effectiveness of the proposed algorithm.
Stability Analysis of DC-link Voltage Control on Autonomous Micro Hydro Power Plant System
Feri Yusivar; M. Shanizal; A. Subiantoro; Gunawan, R
2014-01-01
Micro Hydro Power Plant has become one of the interesting topics to be researched nowadays. This paper deals with the stability analysis on control system of excitation voltage in Micro Hydro Power Plant. The control of this voltage can be achieved by controlling the Permanent Magnet Synchronous Machine (PMSM) with particular algorithm so the voltage on the DC-link part of the system can be controlled. Without knowing the exact specification of system parameters, the system will be most likel...
More stability and robustness with the multi-loop control solution for dynamic voltage restorer (DVR
Directory of Open Access Journals (Sweden)
Abdelkhalek Othmane
2009-01-01
Full Text Available This paper presents the application of dynamic voltage restorers (DVR on power distribution systems for mitigation of voltage sags/swells at critical loads. DVR is one of the compensating types of custom power devices. An adequate modeling and simulation of DVR, including controls in MATLAB, based on forced-commutated voltage source converter (VSC, has been proved suitable for compensating the voltage sags/swells. In this paper, a double loop control method is proposed for the improvement of the stability of DVR during the load current variation. For the main loop (Outer Voltage Loop, we use a PI controller for the regulation of the filter condenser voltage. The second loop (Inner Current Loop also uses a PI controller to control the disturbances current during load variation. Simulation results are presented to illustrate and understand the performances of DVR in the compensation of voltage sags/swell even with variation load condition.
Impact on Generator Reactive Power Limits on a Static Voltage Stability
Directory of Open Access Journals (Sweden)
TOVAR-GONZALEZ, E. A.
2011-11-01
Full Text Available Voltage stability margin in a power system is closely related with the availability of reactive power in the system. Therefore, adequate modeling of the reactive power sources becomes an important issue in this type of studies. The Minimum Singular Value of the load flow Jacobian matrix has been commonly used as a static voltage stability index. In this paper, such index is used to assess the influence on the static voltage stability limit of modeling the generators reactive power limits by its capability curve. Simulation results on a test system indicate that modeling the reactive power limits of the generating units by the simplified Qmin/Qmax approach, commonly used by most of the load flow programs, yields optimistic values for this voltage stability index.
Financial Stability: the Problem of Interpretation
Directory of Open Access Journals (Sweden)
Romaniak Mykola M.
2016-04-01
Full Text Available The article is concerned with studying the problem of interpretation of the concept of «financial stability», allocating the major groups of approaches to its interpretation and clarifying the reasons for absence of a single uniform definition. On the basis of an analysis, approaches to interpretation of the category of «financial stability» have been divided into three main groups. In the definitions by central banks (the first group emphasis is more often placed upon the matter that a system (not necessarily financial is considered stable if it is able to perform all their functions even under conditions of minor adverse shocks and upheavals. The second way to interpretation – by contradiction – must be taken into consideration in the process of studying the financial stability. According to the third group of views, a system can be considered financially stable until the process of transforming savings into investments remains unbroken. The main reasons for the absence of a single clear formulation of the concept of «financial stability» have been identified, namely: different approaches used by scientists to understanding the content of financial system; refocusing from studying the financial stability towards financial crises; accounting the indicator of financial stability in place of the indicator of financial disturbances. A prospective direction for further research is assessment of financial stability through practical consideration of quantitative characteristics that influence on such stability
Institute of Scientific and Technical Information of China (English)
BAO Haibo; WEI Hua
2012-01-01
The traditional voltage stability analysis method is mostly based on the deterministic model, and ignores the uncertainties of bus loads, power supplies, changes in network configuration and so on. However, the great expansion of renewable power generations such as wind and solar energy in a power system has increased their uncertainty, and traditional techniques are limited in capturing their variable behavior. This leads to greater needs of new techniques and methodologies to properly quantify the voltage stability of power systems.
Stabilizing inverse problems by internal data
Kuchment, Peter
2012-07-30
Several newly developing hybrid imaging methods (e.g., those combining electrical impedance or optical imaging with acoustics) enable one to obtain some auxiliary interior information (usually some combination of the electrical conductivity and the current) about the parameters of the tissues. This information, in turn, happens to stabilize the exponentially unstable and thus low-resolution optical and electrical impedance tomography. Various known instances of this effect have been studied individually. We show that there is a simple general technique (covering all known cases) that shows what kinds of interior data stabilize the reconstruction, and why. Namely, we show when the linearized problem becomes an elliptic pseudo-differential one, and thus stable. Stability here is meant as the problem being Fredholm, so the local uniqueness is not shown and probably does not hold in such generality. © 2012 IOP Publishing Ltd.
Stabilizing Inverse Problems by Internal Data
Kuchment, Peter
2011-01-01
Several newly developing hybrid imaging methods (e.g., those combining electrical impedance or optical imaging with acoustics) enable one to obtain some auxiliary interior information (usually some combination of the electrical conductivity and the current) about the parameters of the tissues. This information, in turn, happens to stabilize the exponentially unstable and thus low resolution optical and electrical impedance tomography. Various known instances of this effect have been studied individually. We show that there is a simple general technique (covering all known cases) that shows what kind of interior data stabilizes the reconstruction, and why. Namely, we show when the linearized problem becomes elliptic pseudo-differential one, and thus stable. Stability here is meant as the problem being Fredholm, so the local uniqueness is not shown and probably does not hold in such generality.
DEFF Research Database (Denmark)
Perez, Angel; Jóhannsson, Hjörtur; Lund, P.;
2015-01-01
An approach to evaluate the HVDC interconnectionsmodels to be used in real-time voltage stability assessment is proposed.The existing models for the HVDC interconnections, thatare based on voltage source converter, were studied selecting theones that are suitable for its application in Thevenin...... equivalent ´methods for voltage stability assessment. The proposed methodis to evaluate the validity of the models by using synthetizedPMU measurements from simulations and from PMUs connectedto the danish system. Wide-area measurements are used toestimate the HVDC model parameters which are needed...
Okedu, Kenneth Eloghene; Muyeen, S. M.; Takahashi, Rion; Tamura, Junji
Recent wind farm grid codes require wind generators to ride through voltage sags, which means that normal power production should be re-initiated once the nominal grid voltage is recovered. However, fixed speed wind turbine generator system using induction generator (IG) has the stability problem similar to the step-out phenomenon of a synchronous generator. On the other hand, doubly fed induction generator (DFIG) can control its real and reactive powers independently while being operated in variable speed mode. This paper proposes a new control strategy using DFIGs for stabilizing a wind farm composed of DFIGs and IGs, without incorporating additional FACTS devices. A new current controlled voltage source converter (CC-VSC) scheme is proposed to control the converters of DFIG and the performance is verified by comparing the results with those of voltage controlled voltage source converter (VC-VSC) scheme. Another salient feature of this study is to reduce the number of proportionate integral (PI) controllers used in the rotor side converter without degrading dynamic and transient performances. Moreover, DC-link protection scheme during grid fault can be omitted in the proposed scheme which reduces overall cost of the system. Extensive simulation analyses by using PSCAD/EMTDC are carried out to clarify the effectiveness of the proposed CC-VSC based control scheme of DFIGs.
DEFF Research Database (Denmark)
Morais, Hugo; Sousa, Tiago; Perez, Angel
2016-01-01
The need for developing new methodologies in order to improve power system stability has increased due to the recent growth of distributed energy resources. In this paper, the inclusion of a voltage stability index in distributed energy resources scheduling is proposed. Two techniques were used...... resources is presented to analyse the proposed methodology. Additionally, the methodology is tested in a real distribution network....
Supervisory hybrid model predictive control for voltage stability of power networks
Negenborn, R.R.; Beccuti, A.G.; Demiray, T.; Leirens, S.; Damm, G.; De Schutter, B.; Morari, M.
2007-01-01
Emergency voltage control problems in electric power networks have stimulated the interest for the implementation of online optimal control techniques. Briefly stated, voltage instability stems from the attempt of load dynamics to restore power consumption beyond the capability of the transmission a
Genetic Algorithm-Based Artificial Neural Network for Voltage Stability Assessment
Directory of Open Access Journals (Sweden)
Garima Singh
2011-01-01
Full Text Available With the emerging trend of restructuring in the electric power industry, many transmission lines have been forced to operate at almost their full capacities worldwide. Due to this, more incidents of voltage instability and collapse are being observed throughout the world leading to major system breakdowns. To avoid these undesirable incidents, a fast and accurate estimation of voltage stability margin is required. In this paper, genetic algorithm based back propagation neural network (GABPNN has been proposed for voltage stability margin estimation which is an indication of the power system's proximity to voltage collapse. The proposed approach utilizes a hybrid algorithm that integrates genetic algorithm and the back propagation neural network. The proposed algorithm aims to combine the capacity of GAs in avoiding local minima and at the same time fast execution of the BP algorithm. Input features for GABPNN are selected on the basis of angular distance-based clustering technique. The performance of the proposed GABPNN approach has been compared with the most commonly used gradient based BP neural network by estimating the voltage stability margin at different loading conditions in 6-bus and IEEE 30-bus system. GA based neural network learns faster, at the same time it provides more accurate voltage stability margin estimation as compared to that based on BP algorithm. It is found to be suitable for online applications in energy management systems.
Institute of Scientific and Technical Information of China (English)
TIAN Qing; LIN Xiang-ning
2009-01-01
Recent events related to power system failure have shown that voltage collapse can be a cause of widespread outages.The thrust of this paper is to discuss and establish means of mitigating system voltage instability by using a combination of both reactive current droop compensation and line drop compensation.It is shown that the point that the voltage regulator controls can be defined by a new method which is based on a widely accepted vohage stability analysis tool.This tool can be used to determine which generators will have an impact on the maximum permissible loading of a bus.Dynamic analysis was carried out on the CIGRE Nordic test system to study the impact of control point location on time to collapse and it is shown that the new scheme can improve the voltage stability.
Genetic Algorithm-Based Artificial Neural Network for Voltage Stability Assessment
Garima Singh; Laxmi Srivastava
2011-01-01
With the emerging trend of restructuring in the electric power industry, many transmission lines have been forced to operate at almost their full capacities worldwide. Due to this, more incidents of voltage instability and collapse are being observed throughout the world leading to major system breakdowns. To avoid these undesirable incidents, a fast and accurate estimation of voltage stability margin is required. In this paper, genetic algorithm based back propagation neural network (GABPNN...
Stability Analysis of DC-link Voltage Control on Autonomous Micro Hydro Power Plant System
Directory of Open Access Journals (Sweden)
Feri Yusivar
2014-12-01
Full Text Available Micro Hydro Power Plant has become one of the interesting topics to be researched nowadays. This paper deals with the stability analysis on control system of excitation voltage in Micro Hydro Power Plant. The control of this voltage can be achieved by controlling the Permanent Magnet Synchronous Machine (PMSM with particular algorithm so the voltage on the DC-link part of the system can be controlled. Without knowing the exact specification of system parameters, the system will be most likely unstable. The DC-link control system is modeled, simulated, and mathematically analyzed so the parameter specification for the stable system can be obtained.
Performance Comparison of Voltage Stability Indices for Weak Bus Identification in Power Systems
Verayiah, R.; Mohamed, A.; Shareef, H.; Zainal Abidin, I. Hj
2013-06-01
Voltage collapse event is identified as complex and localized in nature but its effect is extensive once occurred. The vital effect of voltage collapse would be the total system collapse or blackouts which would cost a large loss to utility companies. Eventually, on- line monitoring of power system stability has become an important factor for electric power utilities. The last utmost option to avert voltage collapse incident from occurring is by the implementation of under voltage load shedding scheme. The identification of location for load shedding is the main motivation of the study. The weakest bus in a power system is identified as the location for load shedding. This location is obtained using voltage stability index Ld. The performance and effectiveness of Ld index is compared with Fast Voltage Stability Index (FVSI) and Le Index. The results obtained indicate that Ld Index can be used to identify the weak bus in a power system and consequently for the placement of UVLS relays in a power system network.
Energy Technology Data Exchange (ETDEWEB)
Cardozo Sanchez, Freddy [Mirant Americas (United States); Fernandez Krekeler, Ubaldo [Administracion Nacional de Electricidad (ANDE), Asuncion (Paraguay)
2001-07-01
This document presents analyses of permanent status of the ANDE transmission system, seeking to evaluate the voltage stability and impact that would have possible reinforcements in 500 kV. The transmission under this new voltage level, besides to be a reinforcement to the system for satisfying the national demand, will permit the increase of energy exportation to Brazil, depending on the adopted reinforcement. The system current status and its evolution according to the planning of short and medium period are analysed. In the voltage stability evolution, static analysis techniques to draw the Q-V and P-V curves were used, as well as for determination of the system self-values and stability margins.
Stabilization Algorithms for Large-Scale Problems
DEFF Research Database (Denmark)
Jensen, Toke Koldborg
2006-01-01
The focus of the project is on stabilization of large-scale inverse problems where structured models and iterative algorithms are necessary for computing approximate solutions. For this purpose, we study various iterative Krylov methods and their abilities to produce regularized solutions. Some......-curve. This heuristic is implemented as a part of a larger algorithm which is developed in collaboration with G. Rodriguez and P. C. Hansen. Last, but not least, a large part of the project has, in different ways, revolved around the object-oriented Matlab toolbox MOORe Tools developed by PhD Michael Jacobsen. New...
Harmonics and voltage stability analysis in power systems including thyristor-controlled reactor
Indian Academy of Sciences (India)
M Uzunoglu
2005-02-01
In this study, non-sinusoidal quantities and voltage stability, both known as power quality criteria, are examined together in detail. The widespread use of power electronics elements cause the existence of signiﬁcant non-sinusoidal quantities in the system. These non-sinusoidal quantities can create serious harmonic distortions in transmission and distribution systems. In this paper, harmonic generation of a static VAR compensator with thyristor-controlled reactor and effects of the harmonics on steady-state voltage stability are examined for various operational conditions.
Fast voltage stability assessment and reinforcement in an interconnected power system
Hsiao, Wen-Ta
1998-12-01
It is believed that voltage stability analysis will be more difficult due to the full utilization of transmission systems and the growth of inter-utility power transfer. An online voltage stability analyzing system which can be incorporated into the EMS to deal with the threats of suddenly arising voltage collapses is presented. Operating margin prediction, voltage stability assessment and reinforcement are three major functions. Two predicting methods are proposed to calculate the operating margin according to current operating condition and the anticipative system state. A fast risk indicator based on the saddle-node bifurcation theory is designed to predict the proximity of a system to voltage collapse. A novel CPF method which can trace the power flow solution path through the nose point without notorious numerical difficulties is presented. Speed is the advantage of former method, while accuracy is the important feature of latter one. Voltage stability assessment is required to predict steady-state conditions of a system following a large number of anticipated transmission branch or generator outages. An efficient and simple method based on voltage sensitivity changing rates is proposed for quickly identify the weak buses in a large-scale system. An effective contingency selection function relying on search algorithms built into power flow solutions is designed to filter out most of harmless contingencies for system operators who are working with rapidly changing load/generation patterns and a wide variety of operating conditions. A contingency evaluation function having the ability to deal with real-time numerous contingencies in a very short period of time is utilized to find high-severity contingencies. Var compensation and load shedding are two remedial measures of reinforcement function. Suitable var compensation scheme has three contributions: extending operating margin to avoid voltage collapses, fully utilizing the transmission infrastructure to earn
Numerical stability in problems of linear algebra.
Babuska, I.
1972-01-01
Mathematical problems are introduced as mappings from the space of input data to that of the desired output information. Then a numerical process is defined as a prescribed recurrence of elementary operations creating the mapping of the underlying mathematical problem. The ratio of the error committed by executing the operations of the numerical process (the roundoff errors) to the error introduced by perturbations of the input data (initial error) gives rise to the concept of lambda-stability. As examples, several processes are analyzed from this point of view, including, especially, old and new processes for solving systems of linear algebraic equations with tridiagonal matrices. In particular, it is shown how such a priori information can be utilized as, for instance, a knowledge of the row sums of the matrix. Information of this type is frequently available where the system arises in connection with the numerical solution of differential equations.
Voltage Stability Impact of Grid-Tied Photovoltaic Systems Utilizing Dynamic Reactive Power Control
Omole, Adedamola
Photovoltaic (PV) DGs can be optimized to provide reactive power support to the grid, although this feature is currently rarely utilized as most DG systems are designed to operate with unity power factor and supply real power only to the grid. In this work, the voltage stability of a power system embedded with PV DG is examined in the context of the high reactive power requirement after a voltage sag or fault. A real-time dynamic multi-function power controller that enables renewable source PV DGs to provide the reactive power support necessary to maintain the voltage stability of the microgrid, and consequently, the wider power system is proposed. The loadability limit necessary to maintain the voltage stability of an interconnected microgrid is determined by using bifurcation analysis to test for the singularity of the network Jacobian and load differential equations with and without the contribution of the DG. The maximum and minimum real and reactive power support permissible from the DG is obtained from the loadability limit and used as the limiting factors in controlling the real and reactive power contribution from the PV source. The designed controller regulates the voltage output based on instantaneous power theory at the point-of-common coupling (PCC) while the reactive power supply is controlled by means of the power factor and reactive current droop method. The control method is implemented in a modified IEEE 13-bus test feeder system using PSCADRTM power system analysis software and is applied to the model of a Tampa ElectricRTM PV installation at Lowry Park Zoo in Tampa, FL. This dissertation accomplishes the systematic analysis of the voltage impact of a PV DG-embedded power distribution system. The method employed in this work bases the contribution of the PV resource on the voltage stability margins of the microgrid rather than the commonly used loss-of-load probability (LOLP) and effective load-carrying capability (ELCC) measures. The results of
The Problem of Three Stars: Stability Limit
Valtonen, M.; Mylläri, A.; Orlov, V.; Rubinov, A.
2008-05-01
The problem of three stars arises in many connections in stellar dynamics: three-body scattering drives the evolution of star clusters, and bound triple systems form long-lasting intermediate structures in them. Here we address the question of stability of triple stars. For a given system the stability is easy to determine by numerical orbit calculation. However, we often have only statistical knowledge of some of the parameters of the system. Then one needs a more general analytical formula. Here we start with the analytical calculation of the single encounter between a binary and a single star by Heggie (1975). Using some of the later developments we get a useful expression for the energy change per encounter as a function of the pericenter distance, masses, and relative inclination of the orbit. Then we assume that the orbital energy evolves by random walk in energy space until the accumulated energy change leads to instability. In this way we arrive at a stability limit in pericenter distance of the outer orbit for different mass combinations, outer orbit eccentricities and inclinations. The result is compared with numerical orbit calculations.
Reliability Evaluation of Power System Considering Voltage Stability and Continuation Power Flow
Directory of Open Access Journals (Sweden)
R. K. Saket
2007-06-01
Full Text Available This article describes the methodology for evaluation of the reliability of an composite electrical power system considering voltage stability and continuation power flow, which takes into account the peak load and steady state stability limit. The voltage stability is obtained for the probable outage of transmission lines and removal of generators along with the combined state probabilities. The loss of load probabilities (LOLP index is evaluated by merging the capacity probability with load model. State space is truncated by assuming the limits on total numbers of outages of generators and transmission lines. A prediction correction technique has been used along with one dimensional search method to get optimized stability limit for each outage states. The algorithm has been implemented on a six-bus test system.
Enhancement of Voltage Stability of DC Smart Grid During Islanded Mode by Load Shedding Scheme
Nassor, Thabit Salim; Senjyu, Tomonobu; Yona, Atsushi
2015-10-01
This paper presents the voltage stability of a DC smart grid based on renewable energy resources during grid connected and isolated modes. During the islanded mode the load shedding, based on the state of charge of the battery and distribution line voltage, was proposed for voltage stability and reservation of critical load power. The analyzed power system comprises a wind turbine, a photovoltaic generator, storage battery as controllable load, DC loads, and power converters. A fuzzy logic control strategy was applied for power consumption control of controllable loads and the grid-connected dual active bridge series resonant converters. The proposed DC Smart Grid operation has been verified by simulation using MATLAB® and PLECS® Blockset. The obtained results show the effectiveness of the proposed method.
Improved Thévenin equivalent methods for real-time voltage stability assessment
DEFF Research Database (Denmark)
Perez, Angel; Jóhannsson, Hjörtur; Østergaard, Jacob;
2016-01-01
An improved Thévenin equivalent method for real-time voltage stability assessment that uses wide-area information from synchrophasors is proposed. The improvements are a better modeling of the limited synchronous generators, and a processing that anticipates the effect of field current limiters, ...
Nastasi, Michael Anthony; Wang, Yongqiang; Fraboni, Beatrice; Cosseddu, Piero; Bonfiglio, Annalisa
2013-06-11
Organic thin film devices that included an organic thin film subjected to a selected dose of a selected energy of ions exhibited a stabilized mobility (.mu.) and threshold voltage (VT), a decrease in contact resistance R.sub.C, and an extended operational lifetime that did not degrade after 2000 hours of operation in the air.
Suitability of voltage stability study methods for real-time assessment
DEFF Research Database (Denmark)
Perez, Angel; Jóhannsson, Hjörtur; Vancraeyveld, Pieter;
2013-01-01
This paper analyzes the suitability of existing methods for long-term voltage stability assessment for real-time operation. An overview of the relevant methods is followed with a comparison that takes into account the accuracy, computational efficiency and characteristics when used for security...
DEFF Research Database (Denmark)
Perez, Angel; Jóhannsson, Hjörtur; Østergaard, Jacob
2014-01-01
The possibilities offered by the use of Phasor Measurement Units (PMU) in real - time monitoring provide interesting ways to ensure secure operation of power systems. This paper studies the specific case of voltage stability and the possible improvements to the Thevenin equivalent methods, which...
Energy Technology Data Exchange (ETDEWEB)
Sahoo, N.C. [Faculty of Engineering and Technology, Multimedia University, Jalan Ayer Keroh Lama, Bukit Beruang, 75450 Melaka (Malaysia); Prasad, K. [Faculty of Information Science and Technology, Multimedia University, Jalan Ayer Keroh Lama, Bukit Beruang, 75450 Melaka (Malaysia)
2006-11-15
This paper presents a fuzzy genetic approach for reconfiguration of radial distribution systems (RDS) so as to maximize the voltage stability of the network for a specific set of loads. The network reconfiguration involves a mechanism for selection of the best set of branches to be opened, one from each loop, such that the reconfigured RDS possesses desired performance characteristics. This discrete solution space is better handled by the proposed scheme, which maximizes a suitable optimizing function (computed using two different approaches). In the first approach, this function is chosen as the average of a voltage stability index of all the buses in the RDS, while in the second approach, the complete RDS is reduced to a two bus equivalent system and the optimizing function is the voltage stability index of this reduced two bus system. The fuzzy genetic algorithm uses a suitable coding and decoding scheme for maintaining the radial nature of the network at every stage of genetic evolution, and it also uses a fuzzy rule based mutation controller for efficient search of the solution space. This method, tested on 69 bus and 33 bus RDSs, shows promising results for the both approaches. It is also observed that the network losses are reduced when the voltage stability is enhanced by the network reconfiguration. (author)
VOLTAGE STABILITY OF SHORT TRANSMISSION LINE EQUIPPED WITH A THYRISTOR CONTROLLED SERIES CAPACITOR
Directory of Open Access Journals (Sweden)
Prechanon Kumkratug
2012-01-01
Full Text Available It is becoming increasingly important to fully utilize the existing transmission system assets due to environmental legislation, rights-of-way issues, costs of construction and deregulation policies that introduced in recent years. The Thyristor Controlled Series Capacitor (TCSC has been proposed for the better control power flow and dynamic performance. The exact short transmission line model consists of the resistance and reactance. Most of previous researches studies voltage stability performance of the TCSC in SMIB System with neglecting the resistance of the line. Thus the fully capability of the TCSC on voltage stability improvement of power system may not be applied. The consideration of the resistance causes in the difficulty of deriving the mathematical model. This study investigates the effect of the TCSC on voltage stability of the power system with consideration the exact short transmission line mode. The concept of two-port network is applied to simplify the mathematical model of the power system. The proposed method is tested on sample system and compared on various cases. The first swing of rotor angle curve of the faulted system without resistance is obviously higher than that of with resistance whereas the second swing of the faulted system without resistance is slightly less than that of with resistance. The system with a TCSC can improve voltage stability of power system. It was found from this study that the TCSC and resistance of the line can improve first swing of rotor angle. However, the resistance of the line provides the negative effect on second swing of rotor angle. The simulation results indicate that for practical short line, the resistance is very import parameters for evaluating voltage stability of power system.
Stability and bifurcation in a voltage controlled negative-output KY Boost converter
Wang, Fa-Qiang; Ma, Xi-Kui
2011-03-01
The stability and bifurcation in a voltage controlled negative-output KY Boost converter is studied in this Letter. A glimpse at the stability and bifurcation from the power electronics simulator (PSIM) software are given. And then, its mathematical model and corresponding discrete model are derived. The stability and bifurcation of the converter are determined with the help of the loci of eigenvalues of the Jacobian matrix. It is found that the Hopf bifurcation is easy to come in this converter when the value of its energy-transferring capacitor increases. Finally, the analytical results are confirmed by the circuit experiment.
An Impedance-Based Stability Analysis Method for Paralleled Voltage Source Converters
DEFF Research Database (Denmark)
Wang, Xiongfei; Blaabjerg, Frede; Loh, Poh Chiang
2014-01-01
This paper analyses the stability of paralleled voltage source converters in AC distributed power systems. An impedance-based stability analysis method is presented based on the Nyquist criterion for multiloop system. Instead of deriving the impedance ratio as usual, the system stability...... is assessed based on a series of Nyquist diagrams drawn for the terminal impedance of each converter. Thus, the effect of the right half-plane zeros of terminal impedances in the derivation of impedance ratio for paralleled source-source converters is avoided. The interaction between the terminal impedance...... of converter and the passive network can also be predicted by the Nyquist diagrams. This method is applied to evaluate the current and voltage controller interactions of converters in both grid-connected and islanded operations. Simulations and experimental results verify the effectiveness of theoretical...
Dynamic Voltage Stability Studies using a Modified IEEE 30-Bus System
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Oluwafemi Emmanuel Oni
2016-09-01
Full Text Available Power System stability is an essential study in the planning and operation of an efficient, economic, reliable and secure electric power system because it encompasses all the facet of power systems operations, from planning, to conceptual design stages of the project as well as during the systems operating life span. This paper presents different scenario of power system stability studies on a modified IEEE 30-bus system which is subjected to different faults conditions. A scenario whereby the longest high voltage alternating current (HVAC line is replaced with a high voltage direct current (HVDC line was implemented. The results obtained show that the HVDC line enhances system stability more compared to the contemporary HVAC line. Dynamic analysis using RMS simulation tool was used on DigSILENT PowerFactory.
Voltage Stabilization of a Wind Turbine with STATCOM Using Intelligent Control Techniques
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S. A. Gawish
2016-03-01
Full Text Available Application of FACTS controller called Static Synchronous Compensator STATCOM to improve the performance of power grid with Wind System is investigated. The essential feature of the STATCOM is that it has the ability to absorb or inject fastly reactive power with power grid. Therefore the voltage regulation of the power grid with STATCOM FACTS device is achieved. Moreover restoring the stability of the wind system at suddenly step up or down in wind speed is obtained with STATCOM. This paper describes a complete simulation of voltage regulation of a wind system using STATCOM. Conventional control technique as proportional plus integral controller , and intelligent techniques as FLC and ANFIS are used in this work. The control technique is performed using MATLAB package software. The dynamic response of uncontrolled system is also investigated under wide range of disturbances. The voltage regulation by using STATCOM whose output is varied so as to maintain or control output voltage in the system. The dynamic response of controlled system is shown and comparison between the uncontrolled system and the controlled system is described to assure the validity of the proposed controller. Also comparison between the proposed control methods scheme is presented. To validate the powerful of the STATCOM FACTS controllers, the studied power system is simulated and subjected to different severe disturbances. The results prove the effectiveness of the proposed STATCOM controller in terms of fast damping the power system oscillations and restoring the power system stability and voltage.
Investigation of Voltage Unbalance Problems In Electric Arc Furnace Operation Model
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Yacine DJEGHADER
2013-06-01
Full Text Available In modern steel industry, Electric Arc Furnaces are widely used for iron and scarp melting. The operation of electric arc furnace causes many power quality problems such as harmonics, unbalanced voltage and flicker. The factors that affect Electric arc furnace operation are the melting or refining materials, melting stage, electrodes position (arc length, electrode arm control and short circuit power of the feeder, so, arc voltages, current and power are defined as a nonlinear function of arc length. This study focuses on investigation of unbalanced voltage due to Electrics Arc Furnace operation mode. The simulation results show the major problem of unbalanced voltage affecting secondary of furnace transformer is caused by the different continues movement of electrodes.
Investigation of Voltage Unbalance Problems In Electric Arc Furnace Operation Model
Yacine DJEGHADER; Hocine LABAR
2013-01-01
In modern steel industry, Electric Arc Furnaces are widely used for iron and scarp melting. The operation of electric arc furnace causes many power quality problems such as harmonics, unbalanced voltage and flicker. The factors that affect Electric arc furnace operation are the melting or refining materials, melting stage, electrodes position (arc length), electrode arm control and short circuit power of the feeder, so, arc voltages, current and power are defined as a nonlinear function of ar...
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Hyun-Jin Kim
2015-12-01
Full Text Available In this study, we have proposed the auxiliary bias pulse scheme to improve the stability of atmospheric pressure plasma jets driven by an AC sinusoidal waveform excitation source. The stability of discharges can be significantly improved by the compensation of irregular variation in memory voltage due to the effect of auxiliary bias pulse. From the parametric study, such as the width, voltage, and onset time of auxiliary bias pulse, it has been demonstrated that the auxiliary bias pulse plays a significant role in suppressing the irregular discharges caused by the irregular variation in memory voltage and stable discharge can be initiated with the termination of the auxiliary bias pulse. As a result of further investigating the effects of the auxiliary pulse scheme on the jet stability under various process conditions such as the distance between the jet head and the counter electrode, and carrier gas flow, the jet stability can be improved by adjusting the amplitude and number of the bias pulse depending on the variations in the process conditions.
About one problem of optimal stabilization of linear compound systems
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Barseghyan V.R.
2014-12-01
Full Text Available The problem of optimal stabilization of linear compound system is investigated. Based on Lyapunov function method the method of building optimal stabilizing control action is suggested. The solution of the problem of optimal stabilization of a concrete compound system is given.
A 600kV 15mA Cockcroft-Walton high-voltage power supply with high stability and low-ripple voltage
Energy Technology Data Exchange (ETDEWEB)
Su Tongling [Department of Modern Physics, Lanzhou University, Lanzhou 730000 (China); Zhang Yimin [Department of Modern Physics, Lanzhou University, Lanzhou 730000 (China)]. E-mail: zhangyim03@st.lzu.edu.cn; Chen Shangwen [Department of Modern Physics, Lanzhou University, Lanzhou 730000 (China); Liu Yantong [Department of Modern Physics, Lanzhou University, Lanzhou 730000 (China); Lv Huiyi [Department of Modern Physics, Lanzhou University, Lanzhou 730000 (China); Liu Jiangtao [Department of Modern Physics, Lanzhou University, Lanzhou 730000 (China)
2006-05-10
A Cockcroft-Walton high-voltage power supply with high stability and low-ripple voltage has been developed. This power supply has been operated in a ns pulse neutron generator. The maximum non-load voltage is 600kV while the working voltage and load current are 550kV and 15mA, respectively. The tested results indicate that when the power supply is operated at 300kV, 6.7mA and the input voltage varies +/-10%, the long-term stability of the output voltage is S=(0.300-1.006)x10{sup -3}. The ripple voltage is {delta}U{sub P-P}=6.2V at 300kV, 6.8-8.3mA and the ratio of {delta}U{sub P-P} to the output voltage V{sub H} is {delta}U{sub P-P}/V{sub H}=2.1x10{sup -5}.
A STABILITY THEOREM FOR CONSTRAINED OPTIMAL CONTROL PROBLEMS
Institute of Scientific and Technical Information of China (English)
M.H. Farag
2004-01-01
This paper presents the stability of difference approximations of an optimal control problem for a quasilinear parabolic equation with controls in the coefficients, boundary conditions and additional restrictions. The optimal control problem has been convered to one of the optimization problem using a penalty function technique. The difference approximations problem for the considered problem is obtained. The estimations of stability of the solution of difference approximations problem are proved. The stability estimation of the solution of difference approximations problem by the controls is obtained.
Influence of Wind Plant Ancillary Voltage Control on System Small Signal Stability
DEFF Research Database (Denmark)
Su, Chi; Chen, Zhe
2012-01-01
As a common tendency, large-scale wind farms are increasingly connected to the transmission system of modern power grids. This introduces some new challenges to the connected power systems, and the transmission system operators (TSOs) have to put some new requirements as part of the grid codes...... on the integration of wind farms. One common requirement to wind farms is the function of system voltage control which can be implemented in the grid-side convertor controller of a variable speed wind turbine. This ancillary voltage control provided by wind farms could have some influence on the system small signal...... stability. This paper implements an ancillary voltage control strategy on a direct-drive-full-convertor-based wind farm and studies its influence on the damping ratio values of the dominant oscillation mode within the connected power system. All the calculations and simulations are conducted in DIg...
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Sai Ram Inkollu
2016-09-01
Full Text Available This paper presents a novel technique for optimizing the FACTS devices, so as to maintain the voltage stability in the power transmission systems. Here, the particle swarm optimization algorithm (PSO and the adaptive gravitational search algorithm (GSA technique are proposed for improving the voltage stability of the power transmission systems. In the proposed approach, the PSO algorithm is used for optimizing the gravitational constant and to improve the searching performance of the GSA. Using the proposed technique, the optimal settings of the FACTS devices are determined. The proposed algorithm is an effective method for finding out the optimal location and the sizing of the FACTS controllers. The optimal locations and the power ratings of the FACTS devices are determined based on the voltage collapse rating as well as the power loss of the system. Here, two FACTS devices are used to evaluate the performance of the proposed algorithm, namely, the unified power flow controller (UPFC and the interline power flow controller (IPFC. The Newton–Raphson load flow study is used for analyzing the power flow in the transmission system. From the power flow analysis, bus voltages, active power, reactive power, and power loss of the transmission systems are determined. Then, the voltage stability is enhanced while satisfying a given set of operating and physical constraints. The proposed technique is implemented in the MATLAB platform and consequently, its performance is evaluated and compared with the existing GA based GSA hybrid technique. The performance of the proposed technique is tested with the benchmark system of IEEE 30 bus using two FACTS devices such as, the UPFC and the IPFC.
Voltage Stability Bifurcation Analysis for AC/DC Systems with VSC-HVDC
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Yanfang Wei
2013-01-01
Full Text Available A voltage stability bifurcation analysis approach for modeling AC/DC systems with VSC-HVDC is presented. The steady power model and control modes of VSC-HVDC are briefly presented firstly. Based on the steady model of VSC-HVDC, a new improved sequential iterative power flow algorithm is proposed. Then, by use of continuation power flow algorithm with the new sequential method, the voltage stability bifurcation of the system is discussed. The trace of the P-V curves and the computation of the saddle node bifurcation point of the system can be obtained. At last, the modified IEEE test systems are adopted to illustrate the effectiveness of the proposed method.
Dynamic Stability Analysis of Autonomous Medium-Voltage Mixed-Source Microgrid
DEFF Research Database (Denmark)
Zhao, Zhuoli; Yang, Ping; Guerrero, Josep M.
2015-01-01
In an autonomous microgrid without connection to the interconnected grid to support the frequency and voltage, it is more complex to control and manage. Thus in order to investigate the dynamic stability of the medium-voltage (MV) microgrid in Dongao Island, a detailed small-signal state......-space model of the autonomous MV mixed-source microgrid containing diesel generator set (DGS), grid-supporting battery energy storage system (BESS), squirrel cage induction generator (SCIG) wind turbine and network is developed. Sensitivity analysis is carried out to reveal the dynamic stability margin...... of the MV microgrid and identify the permissible variations range of the droop coefficients. Finally, the theoretical analysis is verified with time-domain simulation and experimental results....
Energy Technology Data Exchange (ETDEWEB)
Taubman, Matthew S.; Phillips, Mark C.
2016-01-12
Systems and methods are disclosed that provide a direct indication of the presence and concentration of an analyte within the external cavity of a laser device that employ the compliance voltage across the laser device. The systems can provide stabilization of the laser wavelength. The systems and methods can obviate the need for an external optical detector, an external gas cell, or other sensing region and reduce the complexity and size of the sensing configuration.
High-efficiency voltage regulator and stabilizer for outdoor lighting installations
Blánquez, F.R.; Rebollo López, Emilio; Blázquez García, Francisco; Platero Gaona, Carlos Antonio; Frías Marín, Pablo
2012-01-01
This paper presents a high performance system of regulation and stabilization of luminous flux for public street lighting installations. Its purpose is to reduce the luminous flux of the luminaries efficiently by reducing their voltage supply, resulting in the improvement of energy efficiency in the installation. The system is basically composed of electromagnetic components which provide robustness and high-performance to the device, as well as minimum maintenance requirements. However, the ...
Assessment of Global Voltage Stability Margin through Radial Basis Function Neural Network
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Akash Saxena
2016-01-01
Full Text Available Dynamic operating conditions along with contingencies often present formidable challenges to the power engineers. Decisions pertaining to the control strategies taken by the system operators at energy management centre are based on the information about the system’s behavior. The application of ANN as a tool for voltage stability assessment is empirical because of its ability to do parallel data processing with high accuracy, fast response, and capability to model dynamic, nonlinear, and noisy data. This paper presents an effective methodology based on Radial Basis Function Neural Network (RBFN to predict Global Voltage Stability Margin (GVSM, for any unseen loading condition of the system. GVSM is used to assess the overall voltage stability status of the power system. A comparative analysis of different topologies of ANN, namely, Feedforward Backprop (FFBP, Cascade Forward Backprop (CFB, Generalized Regression (GR, Layer Recurrent (LR, Nonlinear Autoregressive Exogenous (NARX, ELMAN Backprop, and Feedforward Distributed Time Delay Network (FFDTDN, is carried out on the basis of capability of the prediction of GVSM. The efficacy of RBFN is better than other networks, which is validated by taking the predictions of GVSM at different levels of Additive White Gaussian Noise (AWGN in input features. The results obtained from ANNs are validated through the offline Newton Raphson (N-R method. The proposed methodology is tested over IEEE 14-bus, IEEE 30-bus, and IEEE 118-bus test systems.
Problem of the gyroscopic stabilizer damping
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Šklíba J.
2009-06-01
Full Text Available The gyroscopic stabilization of the vibro-isolation system of an ambulance couch is analyzed. This paper follows several previous papers, which concern the derivation of the complete system of appropriate differential equations and some analyses were provided there, as well. It was supposed that mass matrix, stiffness matrix and gyroscope impulse-moment remain constant and the stability of equilibrium state was solved according to different alternatives of the damping and of the radial correction. Little known theorems of the stability were used there. With respect to these theorems, vibro-isolation systems can be classified according to odd or even number of generalized coordinates.
Stability Problems for Chua System with One Linear Control
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Camelia Pop Arieşanu
2013-01-01
Full Text Available A Hamilton-Poisson realization and some stability problems for a dynamical system arisen from Chua system are presented. The stability and dynamics of a linearized smooth version of the Chua system are analyzed using the Hamilton-Poisson formalism. This geometrical approach allows to deduce the nonlinear stabilization near different equilibria.
Stability Problems for Plates with Short-Term Damageability
Khoroshun, L. P.; Babich, D. V.
2001-02-01
The problem on stability of plates with microdamages simulated by hollow randomly dispersed micropores is considered. Two approaches are proposed to investigate the stability of plates weakened by microdamages. These approaches are based on models well known from the theory of stability of elastoplastic bodies — the concepts of tangent-modulus loading and continuous loading
Nonconservative stability problems of modern physics
Kirillov, Oleg N
2013-01-01
This work gives a complete overview on the subject of nonconservative stability from the modern point of view. Relevant mathematical concepts are presented, as well as rigorous stability results and numerous classical and contemporary examples from mechanics and physics.The book shall serve to present and prospective specialists providing the current state of knowledge in this actively developing field. The understanding of this theory is vital for many areas of technology, as dissipative effects in rotor dynamics orcelestial mechanics.
Venkateswara Rao, B.; Kumar, G. V. Nagesh; Chowdary, D. Deepak; Bharathi, M. Aruna; Patra, Stutee
2017-07-01
This paper furnish the new Metaheuristic algorithm called Cuckoo Search Algorithm (CSA) for solving optimal power flow (OPF) problem with minimization of real power generation cost. The CSA is found to be the most efficient algorithm for solving single objective optimal power flow problems. The CSA performance is tested on IEEE 57 bus test system with real power generation cost minimization as objective function. Static VAR Compensator (SVC) is one of the best shunt connected device in the Flexible Alternating Current Transmission System (FACTS) family. It has capable of controlling the voltage magnitudes of buses by injecting the reactive power to system. In this paper SVC is integrated in CSA based Optimal Power Flow to optimize the real power generation cost. SVC is used to improve the voltage profile of the system. CSA gives better results as compared to genetic algorithm (GA) in both without and with SVC conditions.
A hybrid method for optimal load shedding and improving voltage stability
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V. Tamilselvan
2016-03-01
Full Text Available In this paper, a hybrid method is proposed for reducing the amount of load shedding and voltage collapse. The hybrid method is the combination of Genetic Algorithm (GA and Neural Network (NN. The GA is used by two stages, one is to frame the optimization model and other stage is to generate data set for developing the NN based intelligent load shedding model. The appropriate buses for load shedding are selected based on the sensitivity of minimum eigenvalue of load flow Jacobian with respect to the load shed. The proposed method is implemented in MATLAB working platform and the performance is tested with 6 bus and IEEE 14 bus bench mark system. The result of the proposed hybrid method is compared with the GA based optimization algorithm. The comparison shows that, the proposed method ensures voltage stability with minimum loading shedding.
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Heng-Yi Su
2016-11-01
Full Text Available This paper proposes an efficient approach for the computation of voltage stability margin (VSM in a large-scale power grid. The objective is to accurately and rapidly determine the load power margin which corresponds to voltage collapse phenomena. The proposed approach is based on the impedance match-based technique and the model-based technique. It combines the Thevenin equivalent (TE network method with cubic spline extrapolation technique and the continuation technique to achieve fast and accurate VSM computation for a bulk power grid. Moreover, the generator Q limits are taken into account for practical applications. Extensive case studies carried out on Institute of Electrical and Electronics Engineers (IEEE benchmark systems and the Taiwan Power Company (Taipower, Taipei, Taiwan system are used to demonstrate the effectiveness of the proposed approach.
A Practical Fast Acting Control Scheme For Fuzzy Logic-Based Voltage Stabilization Control
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E. E. EL-Kholy
2005-03-01
Full Text Available This paper presents a simplified control model for stabilizing a load voltage using a switched reactor in parallel with a fixed capacitor of static VAR compensator. Two IGBT’s are used to control the reactance of the switched reactor. A uniform pulse width modulation is used for controlling the two switches. The compensator has a simple control circuit and structure. A complete modeling and numerical simulation for the proposed systems is presented. A high speed Digital Signal Processor is used for implementing proportional-integral (PI and fuzzy load voltage controllers. Experimental results indicate the superiority of fuzzy logic control over the conventional proportional-integral control method. Simulation results are reported and proved to be in good agreement with the relevant experimental results.
Khan Aafreen; Tiwari Prasad Shankarshan
2014-01-01
Power system security is recognized as one of the major problems in many power systems throughout the world. Power system insecurity such as transmission lines being overloaded causes transmission elements cascade outages, which may lead to complete blackout. In accordance with these reasons, the prediction and recognition of voltage instability in power system has particular importance and it makes the network security stronger. This work, by considering the power system continge...
The robust regulation problem with robust stability
Cevik, M.K.K.; Schumacher, J.M.
1999-01-01
Among the most common purposes of control are the tracking of reference signals and the rejection of disturbance signals in the face of uncertainties. The related design problem is called the `robust regulation problem'. Here we investigate the trade-off between the robust regulation constraint and
Long Lifetime DC-Link Voltage Stabilization Module for Smart Grid Application
DEFF Research Database (Denmark)
Wang, Huai; Chung, Henry; Liu, Wenchao
2012-01-01
Power converters enable efficient and flexible control and conversion of electric energy among different smart grid players (i.e. producers, energy storage systems, and loads). One of the expected features of smart grid is that it will be more reliable compared to conventional grid. However, power...... converters are one kind of the lifetime limiting components applied in smart grid. One of the major causes is the malfunction of electrolytic capacitors (E-Caps) which are widely used for stabilizing the dc-link voltage in various types of power converters applied in smart grid. A dc-link module is therefore...
Stability analysis and design of the improved droop controller on a voltage source inverter
DEFF Research Database (Denmark)
Calabria, Mauro; Schumacher, Walter; Guerrero, Josep M.;
2015-01-01
This paper studies the dynamics of a droop-controlled voltage source inverter connected to a stiff grid and addresses the use of the improved droop controller in order to enhance the dynamic behavior of the system. The small-signal stability of the inverter is studied in depth considering...... variations on its droop parameters, providing a general understanding on the functioning of such system. Finally, three methods to tune the dynamic droop gain are introduced and compared, providing analytical, simulation, and experimental results....
Energy Technology Data Exchange (ETDEWEB)
Taylor, Carson W.; Vanleuven, Allen L.; Nordstrom, Jerry M. [Bonneville Power Administration, Portland, OR (United States)
1994-12-31
Electric utilities have become increasing concerned with the possibility of voltage instability and voltage collapse. Although many countermeasures are a possible, control based countermeasures are often the most cost effective. Voltage collapse is often only a threat during unusual conditions such as very high load and major outages. For these low probability conditions, low cost emergency controls may be the only cost effective countermeasures. This paper provides details on a prototype installation by the Bonneville Power Administration of a new low cost emergency control for voltage stability named CAPS (CAPacitor bank series group Shorting). (author) 6 refs., 5 figs.
Robert Lis; Mirosław Łabuzek
2013-01-01
The reactive power balance in the transmission power grid depends on the reactive power produced by the power stations and the value generated by the capacitive power lines and static compensators. Reactive transmission losses become greater than shunt capacitive generation at the turning-point of voltage stability. Then lowering bus voltages drive EPS into voltage collapse point. The paper presents the balance of reactive power depending on the power demand growth, which is then used to esti...
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Koritko N. N.
2009-06-01
Full Text Available The results of an optimization simulation of original manufacturing process and electric characteristics of stabilitrons with stabilizing voltage Ust=(6,5±0,5 V are presented. The flow of manufacturing process of simulated stabilitron includes the n+-type guard rings regions formation in the р-type substrate; the р–n-junction formation in the р-type substrate; intermediate oxide formation; metal deposition. The stabilizing voltage and differential resistance of the stabilitron voltage-current characteristic reverse branch values were received as the result of calculations at the normal, reduced and high temperature.
Modelling, stability and control of voltage behaviour in power supply systems
Energy Technology Data Exchange (ETDEWEB)
Hill, David J. [Sydney Univ., NSW (Australia). Dept. of Electrical Engineering; Hisken, Ian A. [Newcastle Univ., NSW (Australia). Dept. of Electrical and Computer Engineering
1994-12-31
This paper gives an overview of a line of work on mid to long term voltages stability analysis and control in power systems. The results are based on use of a novel approach to dynamic load modelling using aggregate nonlinear structures. In general, the model for the transmission network and supply end dynamics is of the hybrid differential - algebraic - discrete kind. Various stability questions are precisely formulated and analysed in terms of network and load characteristics (steady-state and transient). The results are shown to be a useful framework for deriving criteria of the where, when and how much kind for various control actions such as load Thedding and tap-blocking. (author) 47 refs., 15 figs., 1 tab.
Interfacial Stability in a Two-Layer Benard Problem.
1985-04-01
STABILITY IN A TWO-LAYER BENARD PROBLEM Yuriko Renardy Technical Summary Report #2814 April 1985 I cti- Work Unit Number 2 - Physical Mathematics...34•"• -••’-’• ^ ••’••• VI , •• W -•- • •- ’•"• INTERFACIAL STABILITY IN A TWO-LAYER BENARD PROBLEM Yuriko Renardy I. INTRODUCTION Two layers of fluids are...Subtltl») INTERFACIAL STABILITY IN A TWO-LAYER BENARD PROBLEM 7. AUTMORf.; Yuriko Renardy »• PERFORMING ORGANIZATION NAME AND ADDRESS
On a new approach to asymptotic stabilization problems
Ivanchikov, A. A.; Kornev, A. A.; Ozeritskii, A. V.
2009-12-01
A numerical algorithm for solving the asymptotic stabilization problem by the initial data to a fixed hyperbolic point with a given rate is proposed and justified. The stabilization problem is reduced to projecting the resolving operator of the given evolution process on a strongly stable manifold. This approach makes it possible to apply the results to a wide class of semidynamical systems including those corresponding to partial differential equations. By way of example, a numerical solution of the problem of the asymptotic stabilization of unstable trajectories of the two-dimensional Chafee-Infante equation in a circular domain by the boundary conditions is given.
Directory of Open Access Journals (Sweden)
John E Candelo
2008-01-01
Full Text Available Este artículo presenta una revisión crítica actualizada de los métodos de estudio de la estabilidad de voltaje en sistemas de potencia. Se realiza la descripción y clasificación en orden cronológico de cada una de las técnicas de estudio, para la detección y predicción de la estabilidad de voltaje, desde la identificación del problema en los años 60’s. También se presentan las modificaciones a las técnicas originales y la utilización en la solución a problemas comunes de estabilidad de voltaje presentados en los sistemas de potencia. La comparación de las técnicas se realiza de acuerdo a la información de la literatura y se discuten las ventajas y desventajas de cada técnica de estudio en la solución de los problemas de estabilidad de voltaje.This paper presents the state of the art of methods for studying voltage stability in power systems. Description and chronological classification of each technique for detection and prediction of voltage stability, since the identification of the problem in the 60’s, are done. Also, modifications to the original techniques and their utilization to solve common problems of voltage-stability in the power system are presented. Comparisons of the different techniques were done according to literature information and the advantages and disadvantages of each technique in the solution of voltage stability problems are discussed.
Temporal and voltage stress stability of high performance indium-zinc-oxide thin film transistors
Song, Yang; Katsman, Alexander; Butcher, Amy L.; Paine, David C.; Zaslavsky, Alexander
2017-10-01
Thin film transistors (TFTs) based on transparent oxide semiconductors, such as indium zinc oxide (IZO), are of interest due to their improved characteristics compared to traditional a-Si TFTs. Previously, we reported on top-gated IZO TFTs with an in-situ formed HfO2 gate insulator and IZO active channel, showing high performance: on/off ratio of ∼107, threshold voltage VT near zero, extracted low-field mobility μ0 = 95 cm2/V·s, and near-perfect subthreshold slope at 62 mV/decade. Since device stability is essential for technological applications, in this paper we report on the temporal and voltage stress stability of IZO TFTs. Our devices exhibit a small negative VT shift as they age, consistent with an increasing carrier density resulting from an increasing oxygen vacancy concentration in the channel. Under gate bias stress, freshly annealed TFTs show a negative VT shift during negative VG gate bias stress, while aged (>1 week) TFTs show a positive VT shift during negative VG stress. This indicates two competing mechanisms, which we identify as the field-enhanced generation of oxygen vacancies and the field-assisted migration of oxygen vacancies, respectively. A simplified kinetic model of the vacancy concentration evolution in the IZO channel under electrical stress is provided.
电力系统电压稳定分析方法综述%Analysis Methods for Power System Voltage Stability
Institute of Scientific and Technical Information of China (English)
王卓欣; 李禹鹏
2014-01-01
In order to further explore the mechanism of voltage stability of power system,compared and sum-marized of the existing analysis methods of voltage stability.Static voltage stability analysis is the study of the equilibrium problem of system dynamic equation,can only given the necessary condition of voltage stability. Because of its simple and fast algorithm,it is widely used.Dynamic voltage stability analysis is the study of the deep understanding of the mechanism of voltage stability and important basis and tools for voltage stability control.Introduces the mathematical model for voltage stability as a starting point,the unified mathematical model of the framework,and analyzes the static voltage stability analysis (including the eigenvalue analysis, model analysis,sensitivity analysis,the method of continuous tide and collapse point method)and the dynamic analysis method (the time domain simulation analysis,the small disturbance analysis and bifurcation analysis) of the theoretical basis,mathematical model,the physical significance,scope of application,which can help to provide the reference of reasonable selection of power system voltage stability analysis method.%为了进一步探索电力系统的电压稳定机制，对已有的电压稳定分析方法进行了比较和总结。电压稳定静态分析法研究的是系统动态方程的平衡点问题，只能给出电压稳定的必要条件，由于算法简单快速，得到广泛应用；电压稳定动态分析法研究的是深入理解电压稳定机理和进行电压稳定控制的重要基础和工具。介绍了以电压稳定数学模型为出发点，在统一的数学模型框架内，分析了电压稳定静态分析法（包括特征值分析法、模式分析法、灵敏度分析法、连续潮流法和崩溃点法）和动态分析法（时域仿真分析法、小扰动分析法和分岔分析法）的理论基础、数学模型、物理意义、适用范围等信息，以期为合理选
Locational Pricing to Mitigate Voltage Problems Caused by High PV Penetration
Directory of Open Access Journals (Sweden)
Sam Weckx
2015-05-01
Full Text Available In this paper, a locational marginal pricing algorithm is proposed to control the voltage in unbalanced distribution grids. The increasing amount of photovoltaic (PV generation installed in the grid may cause the voltage to rise to unacceptable levels during periods of low consumption. With locational prices, the distribution system operator can steer the reactive power consumption and active power curtailment of PV panels to guarantee a safe network operation. Flexible loads also respond to these prices. A distributed gradient algorithm automatically defines the locational prices that avoid voltage problems. Using these locational prices results in a minimum cost for the distribution operator to control the voltage. Locational prices can differ between the three phases in unbalanced grids. This is caused by a higher consumption or production in one of the phases compared to the other phases and provides the opportunity for arbitrage, where power is transferred from a phase with a low price to a phase with a high price. The effect of arbitrage is analyzed. The proposed algorithm is applied to an existing three-phase four-wire radial grid. Several simulations with realistic data are performed.
Effect of FACTS Type to Optimization Performance and Voltage Stability for Electrical Network
Directory of Open Access Journals (Sweden)
Marouani Ismail
2014-01-01
Full Text Available In this paper, a multi objective evolutionary algorithm (MOEA to solve optimal reactive power (VAR dispatch problem with flexible AC transmission system (FACTS devices is presented. This nonlinear multi objective problem (MOP consists to minimize simultaneously real power loss in transmission lines and voltage deviation at load buses, by tuning parameters and location of FACTS. The constraints of this MOP are divided to equality constraints represented by load flow equations and inequality constraints such as, generation VAR sources and security limits at load buses. Two types of FACTS devices, thyristor controlled series capacitor (TCSC and unified power flow controller (UPFC are considered. The design problem is tested on the IEEE 30-bus system.
Thouta, Samrat; Hull, Christina M; Shi, Yu Patrick; Sergeev, Valentine; Young, James; Cheng, Yen M; Claydon, Thomas W
2017-01-24
Slow deactivation of hERG channels is critical for preventing cardiac arrhythmia yet the mechanistic basis for the slow gating transition is unclear. Here, we characterized the temporal sequence of events leading to voltage sensor stabilization upon membrane depolarization. Progressive increase in step depolarization duration slowed voltage-sensor return in a biphasic manner (τfast = 34 ms, τslow = 2.5 s). The faster phase of voltage-sensor return slowing correlated with the kinetics of pore opening. The slower component occurred over durations that exceeded channel activation and was consistent with voltage sensor relaxation. The S4-S5 linker mutation, G546L, impeded the faster phase of voltage sensor stabilization without attenuating the slower phase, suggesting that the S4-S5 linker is important for communications between the pore gate and the voltage sensor during deactivation. These data also demonstrate that the mechanisms of pore gate-opening-induced and relaxation-induced voltage-sensor stabilization are separable. Deletion of the distal N-terminus (Δ2-135) accelerated off-gating current, but did not influence the relative contribution of either mechanism of stabilization of the voltage sensor. Lastly, we characterized mode-shift behavior in hERG channels, which results from stabilization of activated channel states. The apparent mode-shift depended greatly on recording conditions. By measuring slow activation and deactivation at steady state we found the "true" mode-shift to be ∼15 mV. Interestingly, the "true" mode-shift of gating currents was ∼40 mV, much greater than that of the pore gate. This demonstrates that voltage sensor return is less energetically favorable upon repolarization than pore gate closure. We interpret this to indicate that stabilization of the activated voltage sensor limits the return of hERG channels to rest. The data suggest that this stabilization occurs as a result of reconfiguration of the pore gate upon opening by
FERGHANA VALLEY: PROBLEMS OF MAINTAINING ECONOMIC STABILITY
2007-01-01
The Central Asia region, which is located in the very heart of the vast Eurasian continent at the crossroads where four of the largest civilizations (Russian, Chinese, Indian, and Islamic) meet, has a long and profuse history teeming with difficulties and conflicts. The Ferghana Valley is a territory where all the problems of the Central Asia region (border conflicts, poverty, shortage of fertile land and water resources, unemployment, ethnic disputes, and so on) are concentrated and come tog...
Well-posedness and stability for abstract spline problems
Miglierina, E.; Molho, E.
2007-09-01
In this work well-posedness and stability properties of the abstract spline problem are studied in the framework of reflexive spaces. Tykhonov well-posedness is proved without restrictive assumptions. In the context of Hilbert spaces, also the stronger notion of Levitin-Polyak well-posedness is established. A sequence of parametric problems converging to the given abstract spline problem is considered in order to study stability. Under natural assumptions, convergence results for sequences of solutions of the perturbed problems are obtained.
Stability problem for singular Dirac equation system on finite interval
Ercan, Ahu; Panakhov, Etibar
2017-01-01
In this study, we show the stability problem for the singular Dirac equation system respect to two spectra on finite interval. The meaning of the stability problem of differential operators is to estimate difference of the spectral functions which considered problems when a finite number of eigenvalues of these problems coincide. The method is based on work by Ryabushko in [12]. The author in [12] studied to what extent only finitely many eigenvalues in one or both spectra determine the potential. We obtain a bound on variation of difference of the spectral functions for singular Dirac equation system.
11th International Seminar on Stability Problems for Stochastic Models
Zolotarev, Vladimir
1989-01-01
Traditionally the Stability seminar, organized in Moscow but held in different locations, has dealt with a spectrum of topics centering around characterization problems and their stability, limit theorems, probabil- ity metrics and theoretical robustness. This volume likewise focusses on these main topics in a series of original and recent research articles.
The stability for the Cauchy problem for elliptic equations
Alessandrini, Giovanni; Rosset, Edi; Vessella, Sergio
2009-01-01
We discuss the ill-posed Cauchy problem for elliptic equations, which is pervasive in inverse boundary value problems modeled by elliptic equations. We provide essentially optimal stability results, in wide generality and under substantially minimal assumptions. As a general scheme in our arguments, we show that all such stability results can be derived by the use of a single building brick, the three-spheres inequality.
Energy Technology Data Exchange (ETDEWEB)
Costa, Vander Menengoy da; Rosa, Arlei Lucas de Sousa [Department of Electrical Engineering, Federal University of Juiz de Fora, Campus Universitario - Bairro Martelos, 36036-330 Juiz de Fora - MG (Brazil); Guedes, Magda Rocha [Federal Center of Technologic Education of Minas Gerais - CEFET, Rua Jose Peres, 558 36700-000 Leopoldina - MG (Brazil); Cantarino, Marcelo [Centrais Eletricas Brasileiras S.A - ELETROBRAS, Av. Rio Branco, 53, Centro, 14 andar, 20090-004 Rio de Janeiro - RJ (Brazil)
2010-05-15
This paper presents new mathematical models to compute the loading margin, as well as to perform the sensitivity analysis of loading margin with respect to different electric system parameters. The innovative idea consists of evaluating the performance of these methods when the power flow equations are expressed with the voltages in rectangular coordinates. The objective is to establish a comparative process with the conventional models expressed in terms of power flow equations with the voltages in polar coordinates. IEEE test system and a South-Southeastern Brazilian network are used in the simulations. (author)
Energy Technology Data Exchange (ETDEWEB)
Leon Rodriguez, Daniel
2000-12-15
The economic development of the countries has taken implicit a growing industrialization the one which, joined to those every time bigger resident's necessities, it has caused a constant and progressive increment in the electric power demand. However, in the last years the growth of the electric network of these systems has been more and more limited for diverse such factors as the ecology and the economy, as well as for the social and political costs that implies each new construction in the system. With the presence of these restrictions the electric systems in many cases, have been forced to satisfy the increments in the demand making a more exhaustive use of the infrastructure that they have available and the incorporation of only a few new system elements or constructions. These aspects have caused such systems to operate with more limited security margins and that their stability has to be analyzed in a reliable and precise way. Taking into account the previously mentioned aspects, as the electric systems have had the necessity of operating under forced conditions to satisfy the load demand, voltage stability problems have been presented with more frequency causing serious disturbances and in some cases, total blackouts. With these problems, the voltage stability analysis has taken bigger importance in the studies that the electric utilities carry out. This issue has caused that bigger resources are dedicated for the investigation of this phenomenon with the purpose of understanding and developing tools that allow studying it in a more complete and more truthful way. Modal analysis is one of the most recent and popular steady techniques the one that, from its appearance has had a great peak due to the valuable and quick information that provides, besides its implementation easiness and the little effort computational that it requires. In this work is carried out the voltage stability evaluation of a real electric system applying in a combined way the
Energy Technology Data Exchange (ETDEWEB)
Hernandez Alvarez, Enrique
2001-09-15
The research work presented in this thesis, is centered in the voltage stability analysis of medium term considering the effect of the load characteristics and its interaction with the voltage control device models in the transmission network. More concretely, a type of load model is defined and studied with desirable characteristics for the study of the voltage stability, the generic load models derived from field tests and from the application of identification techniques and it is analyzed the influence of the application of control systems to improve the system stability margins. Also, alternatives to the power system modeling for the voltage stability study in complex systems are reviewed. In the first place a fundamental analysis of the voltage characteristics and stability in a simplified power system is presented and the method of adopted analysis is introduced. It is shown that the instability phenomenon is manifested as a singular type bifurcation induced from the critical way of voltage when the system is operated under stress conditions. Next, the contribution of the action of the control devices to the stability margin is analyzed and criteria of the stability analyses are deducted based on the study of such mode. Following a linear model of the power system with desirable characteristics for the study of the voltage stability of medium term is proposed and the characteristics of stability in the context of the study of complex systems are interpreted. The proposed analysis tool is based on the physical notion that the behavior of the voltage control systems in the generators is very rapid with regard to the behavior of the load and has its main application in the preliminary study of the voltage stability of medium and long term. From this model, an analytical tool based on the application of techniques of linear analysis is proposed to approach the problem of determination of critical voltage areas and the contribution of control devices to the
Embedding security constraints into the stabilizers coordination problem
Energy Technology Data Exchange (ETDEWEB)
Ramirez, J.M.; Tapia, R.O.; Castillo, I.T.; Davalos, R.M. [CINVESTAV - Unidad Guadalajara, Jalisco (Mexico)
2004-12-01
The aim of this paper is to expose a fashion to introduce transient stability constraints into the problem of stabilizers coordination solved by an optimal criterion. The problem is posed in such a way that different operating conditions and fault locations may be taken into account, leading to robust stabilizers. The proposed procedure is based on minimizing the incremental real part of modes of concern; such increments are evaluated through second order sensitivities. Inequality constraints are embedded into the problem in order to circumscribe the angular excursions by the stabilizers' action. A nine-bus power system is considered as a sample system to exhibit the main results of the proposed methodology. (author)
Performance, stability and operation voltage optimization of screen-printed aqueous supercapacitors
Lehtimäki, Suvi; Railanmaa, Anna; Keskinen, Jari; Kujala, Manu; Tuukkanen, Sampo; Lupo, Donald
2017-01-01
Harvesting micropower energy from the ambient environment requires an intermediate energy storage, for which printed aqueous supercapacitors are well suited due to their low cost and environmental friendliness. In this work, a systematic study of a large set of devices is used to investigate the effect of process variability and operating voltage on the performance and stability of screen printed aqueous supercapacitors. The current collectors and active layers are printed with graphite and activated carbon inks, respectively, and aqueous NaCl used as the electrolyte. The devices are characterized through galvanostatic discharge measurements for quantitative determination of capacitance and equivalent series resistance (ESR), as well as impedance spectroscopy for a detailed study of the factors contributing to ESR. The capacitances are 200–360 mF and the ESRs 7.9–12.7 Ω, depending on the layer thicknesses. The ESR is found to be dominated by the resistance of the graphite current collectors and is compatible with applications in low-power distributed electronics. The effects of different operating voltages on the capacitance, leakage and aging rate of the supercapacitors are tested, and 1.0 V found to be the optimal choice for using the devices in energy harvesting applications. PMID:28382962
Stability of the magnetomechanical problem in magnetic shape memory alloys
Chatzigeorgiou, George; Haldar, Krishnendu; Lagoudas, Dimitris C.
2010-04-01
In this work we study the unstable phenomena that occur on Magnetic Shape Memory Alloys (MSMAs) during compression tests. Solving the coupled magnetomechanical problem we observe that during the reorientation process the material presents strong non-uniformity, in the form of localized zones, in the distribution of the magnetic, the stress and the strain field. This non-uniformity is due to loss of ellipticity of the coupled problem during the martensitic reorientation and affects significantly the reorientation process. The identification of the stability conditions of the magnetomechanical problem is achieved by performing stability analysis.
Energy Technology Data Exchange (ETDEWEB)
Yesuratnam, G.; Thukaram, D. [Department of Electrical Engineering, Indian Institute of Science, Bangalore 560012 (India)
2007-10-15
This paper presents an approach for alleviation of network over loads in the day-to-day operation of power systems under deregulated environment. The control used for over load alleviation is real power generation rescheduling based on relative electrical distance (RED) concept. The method estimates the relative location of load nodes with respect to the generator nodes. The contribution of each generator for a particular over loaded line is first identified, then based on RED concept the desired proportions of generations for the desired overload relieving is obtained, so that the system will have minimum transmission losses and more stability margins with respect to voltage profiles, bus angles and better transmission tariff. Results obtained for network overload alleviation of suitably modified IEEE 39-bus New England system are presented for illustration purposes. (author)
Stability analysis and dynamic response of a DC-link module with a series voltage compensator
DEFF Research Database (Denmark)
Wang, Huai; Liu, Wenchao; Chung, Henry
2013-01-01
A DC-link module composed of a reduced value of DC-link capacitor and a series voltage compensator has been proposed. The voltage compensator processes the ripple voltage on the DC link and reactive power only, which can be implemented by low-voltage devices. The overall energy storage of the DC...
Institute of Scientific and Technical Information of China (English)
廖青华; 张锐
2011-01-01
阐述了电压稳定的定义与电压失稳机理,对电压稳定与负荷动态特性的关系进行了定性分析,强调了负荷动态特性在电压稳定分析中的重要作用,指出了目前用于电压稳定分析的动态负荷模型存在的问题,说明建立恰当的动态负荷模型是确保电压稳定分析准确性的关键。%Definition of voltage stability and mechanics of voltage collapse are presented. The relationship between voltage stability and Dynamic Load Characteristics is qualitatively analyzed. The importance of Dynamic Load Characteristics in voltage stability analysis is emphasized. The problems of Dynamic Load model in voltage stability analysis at present are pointed out. Appropriate modeling of Dynamic Load is crucial in accurate voltage stability analysis.
Directory of Open Access Journals (Sweden)
Hamed Piarehzadeh
2012-08-01
Full Text Available In this study is tried to optimal distributed generation allocation for stability improvement in radial distribution systems. Voltage instability implies an uncontrolled decrease in voltage triggered by a disturbance, leading to voltage collapse and is primarily caused by dynamics connected with the load. The instability is divided into steady state and transient voltage instability Based on the time spectrum of the incident of the phenomena. The analysis is accomplished using a steady state voltage stability index which can be evaluated at each node of the distribution system. Several optimal capacities and locations are used to check these results. The location of DG has the main effect voltage stability on the system. Effects of location and capacity on incrementing steady state voltage stability in radial distribution systems are examined through Harmony Search Algorithm (HSA and finally the results are compared to Particle Swarm Optimization (PSO on the terms of speed, convergence and accuracy.
A novel mechanism for fine-tuning open-state stability in a voltage-gated potassium channel
DEFF Research Database (Denmark)
Pless, Stephan Alexander; Niciforovic, Ana P; Galpin, Jason D
2013-01-01
Voltage-gated potassium channels elicit membrane hyperpolarization through voltage-sensor domains that regulate the conductive status of the pore domain. To better understand the inherent basis for the open-closed equilibrium in these channels, we undertook an atomistic scan using synthetic fluor...... that the intrinsic open-state destabilization via aromatic repulsion represents a new mechanism by which ion channels, and likely other proteins, fine-tune conformational equilibria.......Voltage-gated potassium channels elicit membrane hyperpolarization through voltage-sensor domains that regulate the conductive status of the pore domain. To better understand the inherent basis for the open-closed equilibrium in these channels, we undertook an atomistic scan using synthetic...... fluorinated derivatives of aromatic residues previously implicated in the gating of Shaker potassium channels. Here we show that stepwise dispersion of the negative electrostatic surface potential of only one site, Phe481, stabilizes the channel open state. Furthermore, these data suggest that this apparent...
DEFF Research Database (Denmark)
Göksu, Ömer; Teodorescu, Remus; Bak, Claus Leth;
2014-01-01
In recent grid codes for wind power integration, wind turbines are required to stay connected during grid faults even when the grid voltage drops down to zero; and also to inject reactive current in proportion to the voltage drop. However, a physical fact, instability of grid-connected converters...... during current injection to very low (close to zero) voltage faults, has been omitted, i.e., failed to be noticed in the previous wind power studies and grid code revisions. In this paper, the instability of grid side converters of wind turbines defined as loss of synchronism (LOS), where the wind...... turbines lose synchronism with the grid fundamental frequency (e.g., 50 Hz) during very deep voltage sags, is explored with its theory, analyzed and a novel stability solution based on PLL frequency is proposed; and both are verified with power system simulations and by experiments on a grid...
Energy Technology Data Exchange (ETDEWEB)
Djukanovic, M. (Inst. ' Nikola Tesla' , Belgrade (Yugoslavia)); Sobajic, D.J.; Yohhan Pao (Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Electrical Engineering and Applied Physics Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Computer Engineering and Science AI WARE inc., Cleveland, OH (United States))
1992-10-01
In heavily stressed power systems, post-fault transient voltage dips can lead to undesired tripping of industrial drives and large induction motors. The lowest transient voltage dips occur when fault clearing times are less than critical ones. In this paper, we propose a new iterative analytical methodology to obtain more accurate estimates of voltage dips at maximum angular swing in direct transient stability analysis. We also propose and demonstrate the possibility of storing the results of these computations in the associative memory (AM) system, which exhibits remarkable generalization capabilities. Feature-based models stored in the AM can be utilized for fast and accurate prediction of the location, duration and the amount of the worst voltage dips, thereby avoiding the need and cost for lengthy time-domain simulations. Numerical results obtained using the example of the New England power system are presented to illustrate our approach. (Author)
DEFF Research Database (Denmark)
Perez, Angel; Møller, Jakob Glarbo; Jóhannsson, Hjörtur;
2014-01-01
This article studies the influence of PMU’s accuracy in voltage stability assessment, considering the specific case of Th ́ evenin equivalent based methods that include wide-area information in its calculations. The objective was achieved by producing a set of synthesized PMU measurements from...
Energy Technology Data Exchange (ETDEWEB)
Fernandez Krekeler, Ubaldo [Administracion Nacional de Electricidad (ANDE), Asuncion (Paraguay)]. E-mail: ufernandez@ieee.org; Cardozo Sanchez, Freddy [Mirant Americas (United States)
2001-07-01
In this work is presented a computational tool to evaluate voltage stability based on statistical analysis techniques. This tool was developed in MATLAB and implements routines through which the Q-V y P-V curves can be obtained, as well as the system self-values in relation to a determined operation point.
2009-01-01
This paper presents the application of dynamic voltage restorers (DVR) on power distribution systems for mitigation of voltage sags/swells at critical loads. DVR is one of the compensating types of custom power devices. An adequate modeling and simulation of DVR, including controls in MATLAB, based on forced-commutated voltage source converter (VSC), has been proved suitable for compensating the voltage sags/swells. In this paper, a double loop control method is proposed for the improvement o...
Stability Analysis of Discontinuous Galerkin Approximations to the Elastodynamics Problem
Antonietti, Paola F.
2015-11-21
We consider semi-discrete discontinuous Galerkin approximations of both displacement and displacement-stress formulations of the elastodynamics problem. We prove the stability analysis in the natural energy norm and derive optimal a-priori error estimates. For the displacement-stress formulation, schemes preserving the total energy of the system are introduced and discussed. We verify our theoretical estimates on two and three dimensions test problems.
Adaptive Voltage Stability Protection Based on Load Identification Using Phasor Measurement Units
DEFF Research Database (Denmark)
Liu, Leo; Bak, Claus Leth; Chen, Zhe
2011-01-01
collapse. In this paper, the online load identification using measurement-based approach based on Phasor Measurement Units (PMU) was proposed to evaluate the proximity to voltage instability in order to prevent voltage collapse. In the scenarios of disturbances, the proximity to voltage collapse...
The Problem of the Instrument Stabilization During Hydrographic Measurements
Directory of Open Access Journals (Sweden)
Felski Andrzej
2016-06-01
Full Text Available Performing any measurement on watercraft is connected with many additional difficulties caused by the sea-environment. The most important is the problem of spatial stabilization of measurement systems, which are usually fastened to craft body. As soon as usually these measurement are executed during the move of the craft additional question is the accuracy of execution the planed trajectory.
浅谈建筑消防给水稳压系统%Discussion on Voltage Stabilization System of Building Fire Water Supply
Institute of Scientific and Technical Information of China (English)
杨国辉
2011-01-01
The paper described several voltage stabilization ways in building fire water supply system, analyzed the form of voltage regulator control system, summed up the problem supercharger regulator facilities should note in practical applications in order to improve the understanding of supercharging regulated facilities for engineering and technical personnel and give full play to regulated facilities.%对建筑消防给水系统的几种稳压方式进行了阐述,分析了稳压系统的控制形式,总结了增压稳压设施在实际应用中应该注意的问题,以提高工程技术人员对增压稳压设施的认识,充分发挥增压稳压设施的作用.
Adaptive Voltage Stability Protection Based on Load Identification Using Phasor Measurement Units
DEFF Research Database (Denmark)
Liu, Leo; Bak, Claus Leth; Chen, Zhe
2011-01-01
collapse. In this paper, the online load identification using measurement-based approach based on Phasor Measurement Units (PMU) was proposed to evaluate the proximity to voltage instability in order to prevent voltage collapse. In the scenarios of disturbances, the proximity to voltage collapse...... with respect to load characteristics was evaluated. Based on different load characteristics, different control and protection schemes were implemented, i.e. shunt capacitor connection, on-load tap changer blocking and load shedding. The results showed that load-based adaptive voltage control and protection...... scheme based on PMUs is promising, as it prevented the voltage collapse and minimized the load shedding area....
Stability of Solutions to Classes of Traveling Salesman Problems.
Niendorf, Moritz; Kabamba, Pierre T; Girard, Anouck R
2016-04-01
By performing stability analysis on an optimal tour for problems belonging to classes of the traveling salesman problem (TSP), this paper derives margins of optimality for a solution with respect to disturbances in the problem data. Specifically, we consider the asymmetric sequence-dependent TSP, where the sequence dependence is driven by the dynamics of a stack. This is a generalization of the symmetric non sequence-dependent version of the TSP. Furthermore, we also consider the symmetric sequence-dependent variant and the asymmetric non sequence-dependent variant. Amongst others these problems have applications in logistics and unmanned aircraft mission planning. Changing external conditions such as traffic or weather may alter task costs, which can render an initially optimal itinerary suboptimal. Instead of optimizing the itinerary every time task costs change, stability criteria allow for fast evaluation of whether itineraries remain optimal. This paper develops a method to compute stability regions for the best tour in a set of tours for the symmetric TSP and extends the results to the asymmetric problem as well as their sequence-dependent counterparts. As the TSP is NP-hard, heuristic methods are frequently used to solve it. The presented approach is also applicable to analyze stability regions for a tour obtained through application of the k -opt heuristic with respect to the k -neighborhood. A dimensionless criticality metric for edges is proposed, such that a high criticality of an edge indicates that the optimal tour is more susceptible to cost changes in that edge. Multiple examples demonstrate the application of the developed stability computation method as well as the edge criticality measure that facilitates an intuitive assessment of instances of the TSP.
Influence of Load Modes on Voltage Stability of Receiving Network at DC/AC System
Directory of Open Access Journals (Sweden)
Mao Chizu
2016-01-01
Full Text Available This paper analyses influence of load modes on DC/AC system. Because of widespread use of HVDC, DC/AC system become more complex than before and the present modes used in dispatch and planning departments are not fit in simulation anymore. So it is necessary to find load modes accurately reflecting characteristics of the system. For the sake of the voltage stability, commutation failure, etc. the practical example of the receiving network in a large DC/AC system in China is simulated with BPA, and the influence of Classical Load Mode (CLM and Synthesis load model (SLM on simulation results is studies. Furthermore, some important parameters of SLM are varied respectively among an interval to analyse how they affect the system. According to this practical examples, the result is closely related to load modes and their parameters, and SLM is more conservative but more reasonable than the present modes. The consequences indicate that at critical states, micro variation in parameters may give rise to change in simulation results radically. Thus, correct mode and parameters are important to enhance simulation accuracy of DC/AC system and researches on how they affect the system make senses.
Genetic Algorithm Used for Load Shedding Based on Sensitivity to Enhance Voltage Stability
Titare, L. S.; Singh, P.; Arya, L. D.
2014-12-01
This paper presents an algorithm to calculate optimum load shedding with voltage stability consideration based on sensitivity of proximity indicator using genetic algorithm (GA). Schur's inequality based proximity indicator of load flow Jacobian has been selected, which indicates system state. Load flow Jacobian of the system is obtained using Continuation power flow method. If reactive power and active rescheduling are exhausted, load shedding is the last line of defense to maintain the operational security of the system. Load buses for load shedding have been selected on the basis of sensitivity of proximity indicator. The load bus having large sensitivity is selected for load shedding. Proposed algorithm predicts load bus rank and optimum load to be shed on load buses. The algorithm accounts inequality constraints not only in present operating conditions, but also for predicted next interval load (with load shedding). Developed algorithm has been implemented on IEEE 6-bus system. Results have been compared with those obtained using Teaching-Learning-Based Optimization (TLBO), particle swarm optimization (PSO) and its variant.
Directory of Open Access Journals (Sweden)
Dahai Zhang
2017-02-01
Full Text Available This paper analyses the effects of doubly fed induction generator (DFIG tidal current turbines on a distribution grid under unbalanced voltage conditions of the grid. A dynamic model of an electrical power system under the unbalanced network is described in the paper, aiming to compare the system performance when connected with and without DFIG at the same location in a distribution grid. Extensive simulations of investigating the effect of DFIG tidal current turbine on stability of the distribution grid are performed, taking into account factors such as the power rating, the connection distance of the turbine and the grid voltage dip. The dynamic responses of the distribution system are examined, especially its ability to ride through fault events under unbalanced grid voltage conditions. The research has shown that DFIG tidal current turbines can provide a good damping performance and that modern DFIG tidal current power plants, equipped with power electronics and low-voltage ride-through capability, can stay connected to weak electrical grids even under the unbalanced voltage conditions, whilst not reducing system stability.
Directory of Open Access Journals (Sweden)
O. BOUHALI
2005-03-01
Full Text Available A novel concept of application of Artificial Neural Networks (ANN for generating the optimum switching functions for the voltage and harmonic control of DC-to-AC bridge inverters is presented. In many research, the neural network is trained off line using the desired switching angles given by the classic harmonic elimination strategy to any value of the modulation index. This limits the utilisability and the precision in other modulation index values. In order to avoid this problem, a new training algorithm is developed without using the desired switching angles but it uses the desired solution of the elimination harmonic equation, i.e. first harmonics are equal to zero. Theoretical analysis of the proposed solving algorithm with neural networks is provided, and simulation results are given to show the high performance and technical advantages of the developed modulator.
Energy Technology Data Exchange (ETDEWEB)
Kim, Miyoung; Kim, Min Su; Kang, Byeong Gyun; Kim, Mi-Kyung; Yoon, Sukin; Lee, Seung Hee [Polymer BIN Fusion Research Center, Department of Polymer Nano-Science and Technology, Chonbuk National University, Chonju, Chonbuk 561-756 (Korea, Republic of); Ge Zhibing; Rao Linghui; Gauza, Sebastian; Wu, Shin-Tson, E-mail: lsh1@chonbuk.ac.k, E-mail: swu@creol.ucf.ed [College of Optics and Photonics, University of Central Florida, Orlando, FL 32816 (United States)
2009-12-07
Polymer-stabilized blue phase liquid crystal displays based on the Kerr effect are emerging due to their submillisecond response time, wide view and simple fabrication process. However, the conventional in-plane switching device exhibits a relatively high operating voltage because the electric fields are restricted in the vicinity of the electrode surface. To overcome this technical barrier, we propose a partitioned wall-shaped electrode configuration so that the induced birefringence is uniform between electrodes throughout the entire cell gap. Consequently, the operating voltage is reduced by {approx} 2.8x with two transistors. The responsible physical mechanisms are explained.
Energy Technology Data Exchange (ETDEWEB)
Morales Gonzalez, Eduardo
2005-12-15
Environmental and economic reasons have been the main factors for limiting the growing of transmission power grids in many countries. In addition, the electric industry trend to de-regulation of electricity markets has forced to operate the transmission grids closer to their normal limits for secure operation. Since most of the time modern power networks operate under stressed conditions, voltage collapse has become a big concern in the daily operation of the systems. Thus, determination of reliable operating limits respect to voltage collapse is of utmost importance to guarantee an economical and secure system operation. With the aim of understanding the mechanisms of voltage stability and voltage collapse, a number of studying approaches have been proposed for the analysis of such problems. A common feature of those approaches is the importance of reliable models for representing load characteristics. As a result of this, the development of adequate mathematical models for reliable load representation has received a great deal of attention. Despite those efforts, load modeling remains as a big challenge in the analysis of power systems voltage stability. In this thesis, the influence of load modeling on voltage stability is addressed using a steady-state analysis approach. The voltage stability analysis of the system is performed from the P-V curves for different load representations and voltage sensitivity indices. Finally, numerical results from two test systems are reported and the close relationship between load modeling and voltage stability limits in a power system is highlighted. [Spanish] Las razones economicas y ambientales han sido los principales factores para limitar el crecimiento de los sistemas de transmision en muchos paises. Ademas, la tendencia a la desregulacion en la industria electrica ha forzado a operar las redes electricas mas cerca de sus limites de operacion. Debido a que la mayoria de los sistemas electricos modernos operan bajo
Stability of charge inversion, Thomson problem, and application to electrophoresis
Patra, Michael; Patriarca, Marco; Karttunen, Mikko
2003-03-01
We analyze charge inversion in colloidal systems at zero temperature using stability concepts, and connect this to the classical Thomson problem of arranging electrons on sphere. We show that for a finite microion charge, the globally stable, lowest-energy state of the complex formed by the colloid and the oppositely charged microions is always overcharged. This effect disappears in the continuous limit. Additionally, a layer of at least twice as many microions as required for charge neutrality is always locally stable. In an applied external electric field the stability of the microion cloud is reduced. Finally, this approach is applied to a system of two colloids at low but finite temperature.
Summary on Voltage Stability of Power Grid in Large-scale Wind Power Area%大规模风电地区电网电压稳定研究综述
Institute of Scientific and Technical Information of China (English)
林泽坤; 彭显刚; 武小梅; 欧英龙
2014-01-01
Rapid development of wind power is more and more threatening voltage stability of power grid in wind power are-a.Therefore,this paper summarizes problem of voltage stability of power grid in large-scale wind power area.It introduces wind power generation model,voltage change calculation for wind power integration,low voltage ride through capability of wind power generator and requirements for low voltage ride through for wind power generator in our country.It analyzes factors affecting voltage stability in wind power area and methods for voltage stability.In addition,it discusses measures for solving voltage stability of power grid in large-scale wind power area.It suggests to strengthen study on voltage stability of power grid in large-scale wind power area in order to ensure safety of power grid in wind power area in aspects of wind pow-er forecast,study on voltage transient wave for wind power integration point at fault time,countermeasures study after wind power generator taking off the grid and coordinated voltage control strategies by thermal power and wind power.%风电的快速发展对风电地区电网电压稳定性威胁越来越大，为此，对国内外大规模风电地区电网电压稳定问题进行了综述。介绍了风力发电模型以及风电并网的电压变化计算以及风机的低电压穿越能力和我国对风机的低电压穿越能力的要求，分析影响风电地区电压稳定的因素和风电地区电网电压稳定的方法，并探讨解决大规模风电地区电网的电压稳定的措施。建议应从风力预测、故障时对风电并网点的电压暂态波形研究、风机脱网后的对应策略研究和火电与风电的配合控制电压策略，加强对大规模风电地区电网电压稳定性研究，保障风电地区的电网安全。
Eigenvalues of a baroclinic stability problem with Ekman damping
Antar, B. N.; Fowlis, W. W.
1980-01-01
An analytical solution is presented for the baroclinic stability problem of a Boussinesq fluid in a beta-plane channel with Ekman suction boundary conditions. All of the modes, stable and unstable, belonging to this problem are identified. It is found that an unstable mode exists for only a certain range of values of the Burger number. The value of the Burger number at the upper limit of this range increases as the Ekman number decreases. Beyond this upper limit only a damped mode exists. It is also found that this transition in parameter space from the unstable to the stable mode occurs in a discontinuous manner.
Leakage current and stability of acrylic elastomer subjected to high DC voltage
Hammami, S.; Jean-Mistral, C.; Jomni, F.; Gallot-Lavallée, O.; Rain, P.; Yangui, B.; Sylvestre, A.
2015-04-01
Dielectric elastomers such as 3M VHB4910 acrylate film have been widely used for electromechanical energy conversion such as actuators, sensors and generators, due to their lightweight, high efficiency, low cost and high energy density. Mechanical and electric properties of such materials have been deeply investigated according to various parameters (temperature, frequency, pre-stress, nature of the compliant electrodes…). Models integrating analytic laws deduced from experiments increase their accuracy. Nevertheless, leakage current and electrical breakdown reduce the efficiency and the lifetime of devices made with these polymers. These two major phenomena are not deeply investigated in the literature. Thus, this paper describes the current-voltage characteristics of acrylate 3M VHB4910 and investigates the stability of the current under high electric field (kV) for various temperatures (from 20°C to 80°C) and over short (300 s) and long (12h) periods. Experimental results show that, with gold electrodes at ambient temperature, the current decreases with time to a stable value corresponding to the conduction current. This decrease occurs during 6 hours, whereas in the literature values of current at short time (less than 1 hour) are generally reported. This decrease can be explained by relaxations mechanisms in the polymer. Schottky emission and Poole-Frenkel emission are both evaluated to explain the leakage current. It emerges from this study that the Schottky effect constitutes the main mechanism of electric current in the 3M VHB4910. For high temperatures, the steady state is reached quickly. To end, first results on the leakage current changes for pre-stretch VHB4910 complete this study.
Gambling Problem Symptom Patterns and Stability across Individual and Timeframe
DEFF Research Database (Denmark)
Nelson, Sarah; Josefsen, Line Gebauer; LaBrie, Richard
2009-01-01
Few studies investigate gambling problems at the symptom level; even fewer investigate how symptom patterns change throughout the course of a gambling disorder. The current study utilized the National Epidemiological Survey on Alcohol and Related Conditions (NESARC; Grant et al., 2004) to investi...... of progression to PG among participants at-risk for PG. The differential diagnostic value of various reported symptoms, as well as their lack of stability, has implications for both researchers and clinicians. 2009 APA, all rights reserved....
Indian Academy of Sciences (India)
M Subbiah; V Ganesh
2010-06-01
We consider the extended Rayleigh problem of hydrodynamic stability dealing with the stability of inviscid homogeneous shear flows in sea straits of arbitrary cross section. We prove a short wave stability result, namely, if $k>0$ is the wave number of a normal mode then $k>k_c$ (for some critical wave number $k_c$) implies the stability of the mode for a class of basic flows. Furthermore, if $K(z)=\\frac{-({U''}_0-T_0{U'}_0)}{U_0-U_{0s}}$, where $U_0$ is the basic velocity, $T_0$ (a constant) the topography and prime denotes differentiation with respect to vertical coordinate then we prove that a sufficient condition for the stability of basic flow is $0 < K(z)≤\\left(\\frac{^2}{D^2}+\\frac{T^2_0}{4}\\right)$, where the flow domain is $0≤ z≤ D$.
The design of the Sepic dc voltage stabilizer%Sepic直流稳压器的设计
Institute of Scientific and Technical Information of China (English)
宋连庆; 宋淑淑
2015-01-01
Designed a range of input voltage is 130~300 V, output 12 V/8 A, the working frequency of 100 kHz Sepic dc voltage stabilizer, this paper expounds the main circuit topology structure, and design input protection circuit sauxiliary power supply circuit, PWM control circuit, optical coupling isolation drive circuit and output over voltage, over current protection circuit, feedback method and pulse width modulation technology is applied to implement the stability of voltage and current output.%设计了一种输入交流电压范围为130～300 V，输出12 V/8 A、工作频率为100 kHz的Sepic直流稳压器，阐述了主电路的拓扑结构，并设计了输入保护电路、辅助电源电路、PWM控制电路、光耦隔离驱动电路与输出过压、过流保护电路，应用反馈手段和脉宽调制技术实现电压、电流的稳定。
El-Zoghby, Helmy M.; Bendary, Ahmed F.
2016-10-01
In this paper Static Synchronous Compensator (STATCOM) is used for improving the performance of the power grid with wind turbine that drives synchronous generator. The main feature of the STATCOM is that it has the ability to absorb or inject rapidly reactive power to grid. Therefore the voltage regulation of the power grid with STATCOM device is achieved. STATCOM also improves the stability of the power system after occurring severe disturbance such as faults, or suddenly step change in wind speed. The proposed STATCOM controller is a Proportional-Integral (PI) controller tuned by Genetic Algorithm (GA). An experimental model was built in Helwan University to the proposed system. The system is tested at different operating conditions. The experimental results prove the effectiveness of the proposed STATCOM controller in damping the power system oscillations and restoring the power system voltage and stability.
Directory of Open Access Journals (Sweden)
V. N. Ananth Duggirala
2015-01-01
Full Text Available Doubly fed induction generator (DFIG is a better alternative to increased power demand. Modern grid regulations force DFIG to operate without losing synchronism during overvoltages called high voltage ride through (HVRT during grid faults. Enhanced field oriented control technique (EFOC was proposed in Rotor Side Control of DFIG converter to improve power flow transfer and to improve dynamic and transient stability. Further electromagnetic oscillations are damped, improved voltage mitigation and limit surge currents for sustained operation of DFIG during voltage swells. The proposed strategy has advantages such as improved reactive power control, better damping of electromagnetic torque oscillations, and improved continuity of voltage and current from stator and rotor to grid during disturbance. In EFOC technique, rotor flux reference changes its value from synchronous speed to zero during fault for injecting current at the rotor slip frequency. In this process, DC-Offset component of stator flux is controlled so that decomposition during overvoltage faults can be minimized. The offset decomposition of flux will be oscillatory in a conventional FOC, whereas in EFOC it is aimed to be quick damping. The system performance with overvoltage of 1.3 times, 1.62 times, and 2 times the rated voltage occurring is analyzed by using simulation studies.
Dragomirescu, Florica Ioana
2012-11-01
The main motivation for a temporal stability investigation of initially localized perturbations in a swirling flow stability problem consists in pointing out the critical frequencies at which instability can sets in, an important key in predicting and understanding the flow particularities. The linearized disturbance equations define a second order ordinary differential equation with non-constant coefficients which we solve in order to determine the critical frequency in different physical parameters spaces. A non-classical polynomials based spectral method is proposed for the numerical treatment of the resulting generalized eigenvalue problem governing the stability of the flow. Numerical investigation are performed in the inviscid case for a moderate level of swirl and dominant temporal instability modes are retrieved for each Fourier component pair. The obtained values of the growth rate associated with the most amplified wavenumber are compared with existing inviscid temporal instability evaluations and good agreements are found.
Institute of Scientific and Technical Information of China (English)
Abdolkhalegh Hamidi; Jamal Beiza; Ebrahim Babaei; Sohrab Khanmohammadi
2016-01-01
An input-output signal selection based on Phillips-Heffron model of a parallel high voltage alternative current/high voltage direct current (HVAC/HVDC) power system is presented to study power system stability. It is well known that appropriate coupling of inputs-outputs signals in the multivariable HVDC-HVAC system can improve the performance of designed supplemetary controller. In this work, different analysis techniques are used to measure controllability and observability of electromechanical oscillation mode. Also inputs–outputs interactions are considered and suggestions are drawn to select the best signal pair through the system inputs-outputs. In addition, a supplementary online adaptive controller for nonlinear HVDC to damp low frequency oscillations in a weakly connected system is proposed. The results obtained using MATLAB software show that the best output-input for damping controller design is rotor speed deviation as out put and phase angle of rectifier as in put. Also response of system equipped with adaptive damping controller based on HVDC system has appropriate performance when it is faced with faults and disturbance.
Analysis of Subgrid Stabilization Method for Stokes-Darcy Problems
Directory of Open Access Journals (Sweden)
Kamel Nafa
2016-01-01
Full Text Available A number of techniques, used as remedy to the instability of the Galerkin finite element formulation for Stokes like problems, are found in the literature. In this work we consider a coupled Stokes-Darcy problem, where in one part of the domain the fluid motion is described by Stokes equations and for the other part the fluid is in a porous medium and described by Darcy law and the conservation of mass. Such systems can be discretized by heterogeneous mixed finite elements in the two parts. A better method, from a computational point of view, consists in using a unified approach on both subdomains. Here, the coupled Stokes-Darcy problem is analyzed using equal-order velocity and pressure approximation combined with subgrid stabilization. We prove that the obtained finite element solution is stable and converges to the classical solution with optimal rates for both velocity and pressure.
Stability, Optimality and Manipulation in Matching Problems with Weighted Preferences
Directory of Open Access Journals (Sweden)
Maria Silvia Pini
2013-11-01
Full Text Available The stable matching problem (also known as the stable marriage problem is a well-known problem of matching men to women, so that no man and woman, who are not married to each other, both prefer each other. Such a problem has a wide variety of practical applications, ranging from matching resident doctors to hospitals, to matching students to schools or, more generally, to any two-sided market. In the classical stable marriage problem, both men and women express a strict preference order over the members of the other sex, in a qualitative way. Here, we consider stable marriage problems with weighted preferences: each man (resp., woman provides a score for each woman (resp., man. Such problems are more expressive than the classical stable marriage problems. Moreover, in some real-life situations, it is more natural to express scores (to model, for example, profits or costs rather than a qualitative preference ordering. In this context, we define new notions of stability and optimality, and we provide algorithms to find marriages that are stable and/or optimal according to these notions. While expressivity greatly increases by adopting weighted preferences, we show that, in most cases, the desired solutions can be found by adapting existing algorithms for the classical stable marriage problem. We also consider the manipulability properties of the procedures that return such stable marriages. While we know that all procedures are manipulable by modifying the preference lists or by truncating them, here, we consider if manipulation can occur also by just modifying the weights while preserving the ordering and avoiding truncation. It turns out that, by adding weights, in some cases, we may increase the possibility of manipulating, and this cannot be avoided by any reasonable restriction on the weights.
DEFF Research Database (Denmark)
Rahimi, Saeed; Wiechowski, W.; Randrup, M.;
2008-01-01
cable in transmission system. The objective of this paper and the companion paper is to address the most important problems expected in transmission system with relatively larger share of long HV underground cables. The end goal will be a guideline to special solutions and precautions to avoid dangerous...... over voltage problems and also resonance problems in a transmission network with future increased share of cables. Two major categories of problems are switching transient and resonance problems. In each category of the possible problems, first some theoretical background is provided...... and then the problem and countermeasures are discussed. In this paper most important resonance problems are addressed and discussed. Three main categories of resonance problems are: Near Resonance, Harmonic resonance and Ferroresonance....
Carpinelli, Guido; Noce, Christian; Russo, Angela; Varilone, Pietro
2014-12-01
Capacitors and series voltage regulators are used extensively in distribution systems to reduce power losses and improve the voltage profile along the feeders. This paper deals with the problem of contemporaneously choosing optimal locations and sizes for both capacitors and series voltage regulators in three-phase, unbalanced distribution systems. This is a mixed, non-linear, constrained, multi-objective optimization problem that usually is solved in deterministic scenarios. However, distribution systems are stochastic in nature, which can lead to inaccurate deterministic solutions. To take into account the unavoidable uncertainties that affect the input data related to the problem, in this paper, we have formulated and solved the multi-objective optimization problem in probabilistic scenarios. To address the multi-objective optimization problem, algorithms were used in which all the objective functions were combined to form a single function. These algorithms allow us to transform the original multi-objective optimization problem into an equivalent, single-objective, optimization problem, an approach that appeared to be particularly suitable since computational time was an important issue. To further reduce the computational efforts, a linearized form of the equality constraints of the optimization model was used, and a micro-genetic algorithm-based procedure was applied in the solution method.
电力系统电压静态稳定性指标述评%REVIEW ON STEADY STATE VOLTAGE STABILITY INDICES OF POWER SYSTEMS
Institute of Scientific and Technical Information of China (English)
周双喜; 姜勇; 朱凌志
2001-01-01
Many steady-state voltage stability indices of power systems are summarized and compared in this paper. According to the demands of steady-state voltage stability analysis the principles and methods of setting up voltage stability indices are proposed.%综述和比较了多种电压静态稳定性指标，根据电压静态稳定性分析的要求提出了建立电压静态稳定性指标的要求和构造方法。
Stability analysis for nonlinear multi－variable delay perturbation problems
Institute of Scientific and Technical Information of China (English)
WangHongshan; ZhangChengjian
2003-01-01
This paper discusses the stability of theoretical solutions for nonlinear multi-variable delay perturbation problems(MVDPP) of the form x′(t) = f(x(t),x(t - τ1(t)),…,x(t -τm(t)),y(t),y(t - τ1(t)),…,y(t - τm(t))), and gy′(t) = g(x(t),x(t- τ1(t)),…,x(t- τm(t)),y(t),y(t- τ1(t)),…,y(t- τm(t))), where 0 < ε <<1. A sufficient condition of stability for the systems is obtained. Additionally we prove the numerical solutions of the implicit Euler method are stable under this condition.
ANALYSIS VOLTAGE STABILITY USING HOPF BIFURCATION THEORY%电压稳定中的Hopf分歧分析
Institute of Scientific and Technical Information of China (English)
王洪哲; 邓集祥
2000-01-01
本文采用Hopf分歧理论结合相关因子法研究探讨电压稳定性问题，Hopf分歧理论比较全面地考虑系统的非线性性态，能够比传统的分析方法更深刻地探讨电力系统在临界点附近的稳定问题，并且能够在一定程度上将功角稳定问题和电压稳定问题联系起来提供统一的数学分析基础。%The combination of the bifurcation theory and relevant factortheory is proposed to search and discuss the voltage stability in this paper. Hopf bifurcation theory can more comprehensively reveal the nonlinear character of the system ,so it can more deeply search and discuss the stability nearby the critical point than the traditional analyzing method. To the extent,it can connect the P-δ stability with the voltage stability and provide the general mathematics analysis foundation.
The Problem of the Instrument Stabilization During Hydrographic Measurements
Felski, Andrzej; Naus, Krzysztof; Wąż, Mariusz
2016-06-01
Performing any measurement on watercraft is connected with many additional difficulties caused by the sea-environment. The most important is the problem of spatial stabilization of measurement systems, which are usually fastened to craft body. As soon as usually these measurement are executed during the move of the craft additional question is the accuracy of execution the planed trajectory. This is a problem for all investigators, especially when system use spatially configured beams of any antennas or other sensors, regardless is it receiving or transmitting one. Different aspects of these question are the subject of research activity of Institute of Navigation and Maritime Hydrography of Polish Naval Academy. In this paper the review of works executed in last years are presented.
Gambling Problem Symptom Patterns and Stability across Individual and Timeframe
DEFF Research Database (Denmark)
Nelson, Sarah; Josefsen, Line Gebauer; LaBrie, Richard
2009-01-01
Few studies investigate gambling problems at the symptom level; even fewer investigate how symptom patterns change throughout the course of a gambling disorder. The current study utilized the National Epidemiological Survey on Alcohol and Related Conditions (NESARC; Grant et al., 2004) to investi......Few studies investigate gambling problems at the symptom level; even fewer investigate how symptom patterns change throughout the course of a gambling disorder. The current study utilized the National Epidemiological Survey on Alcohol and Related Conditions (NESARC; Grant et al., 2004...... of progression to PG among participants at-risk for PG. The differential diagnostic value of various reported symptoms, as well as their lack of stability, has implications for both researchers and clinicians. 2009 APA, all rights reserved....
A 50 Mw Pulse-Forming Network with a Voltage Stability within 0.03-Percent
Meddens, B. J. H.; Delmee, P. F. M.; van Amersfoort, P. W.
1993-01-01
Requirements on electron energy stability are extremely tight for operation of a free-electron laser. In case a radio-frequency field is used to accelerate the electrons, this leads to stringent requirements on the stability of the klystron output power and, hence, on the stability of the source pro
Institute of Scientific and Technical Information of China (English)
YAO Min-Na; FAN Lin-Lin; LIU Ya-Nan; CHEN Qing-Ai; ZENG Yuan; JIAN Wen-Jie; PANG Jie
2011-01-01
Structures of KGM treated in two high-voltage pulse electric fields were characterized by infrared spectroscopy,Raman spectroscopy,X-ray diffraction and so on.The results showed that intermolecular hydrogen bonding interactions of KGM were reduced after being treated with high-voltage pulse electric field,but there was no significant effect on its fiber chain form and thermal characteristics.Results of the study can provide a useful reference for further study on the structure and property of KGM,and especially can provide theoretical basis for the effect of physical field on the foodstuff deep processing related to KGM.
Impact of wind farms voltage regulation on the stability of the network frequency
Energy Technology Data Exchange (ETDEWEB)
Fernandez, R.D. [Laboratorio de Electronica Industrial, Control e Instrumentacion (LEICI), Facultad de Ingenieria, Universidad Nacional de La Plata, CC 91, 1900 La Plata (Argentina); Laboratorio de Electronica. Facultad de Ingenieria, Universidad Nacional de la Patagonia San Juan Bosco, Ciudad Universitaria, Km. 4, 9000 Comodoro Rivadavia (Argentina); Battaiotto, P.E.; Mantz, R.J. [Laboratorio de Electronica Industrial, Control e Instrumentacion (LEICI), Facultad de Ingenieria, Universidad Nacional de La Plata, CC 91, 1900 La Plata (Argentina)
2008-07-15
As it is well known, different kinds of wind farms can contribute to frequency and voltage regulation by means of active and reactive powers, respectively. This paper analyzes how the wind farm reactive power loop, which contribute to voltage regulation, modifies the location of the eigenvalues of a selected power system when the wind power penetration is increased. Previous to this analysis, aspects of the modeling of double fed induction generators in wind energy generation and power systems are discussed. Finally, simulations, which verify the theoretical results are presented. (author)
一种高可靠性开关稳压电源的研制%The Development of the High Reliable Switching Voltage Stabilizer
Institute of Scientific and Technical Information of China (English)
王建; 赵福成; 单世东
2001-01-01
介绍一种变电站用的开关稳压电源,分析其主电路及控 制电路的原理,及其高可靠性。%The switching voltage stabilizer for the transformer substation is presented. Th e principle of the main circuit and control circuit is analysed. This switching voltage stabilizer is high reliable.
Power System Stability Using Decentralized Under Frequency and Voltage Load Shedding
DEFF Research Database (Denmark)
Hoseinzadeh, Bakhtyar; Silva, Filipe Faria Da; Bak, Claus Leth
2014-01-01
of disturbance location. In this paper, to aim adaptive performance of the relays, the amount of load shed in each stage is determined proportional to the measured Rate of Change of Frequency (ROCOF). In order to localize the LS scheme close to the disturbance place, this scheme utilizes the voltage drop...
Successful application of Low Voltage Electron Microscopy to practical materials problems
Energy Technology Data Exchange (ETDEWEB)
Bell, David C., E-mail: dcb@seas.harvard.edu [School of Engineering and Applied Sciences, Harvard University, Cambridge, MA (United States); Center for Nanoscale Systems, Harvard University, Cambridge, MA (United States); Mankin, Max; Day, Robert W. [Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA (United States); Erdman, Natasha [JEOL USA Inc. Peabody, MA (United States)
2014-10-15
Low-voltage High-Resolution Electron Microscopy (LVHREM) has several advantages, including increased cross-sections for inelastic and elastic scattering, increased contrast per electron, decreased delocalization effects and reduced knock-on damage. Imaging at differing voltages has shown advantages for imaging materials that are knock-on damage sensitive. We show experimentally that different materials systems benefit from low voltage high-resolution microscopy. There are advantages for imaging single layer materials such as graphene at below the knock-on threshold; we present an example of imaging a graphene sheet at 40 kV. We have also examined mesoporous silica decorated with Pd nanoparticles and carbon black functionalized with Pd/Pt nanoparticles. In these cases we show that the lower voltage imaging maintains the structure of the surrounding matrix during imaging, whereas aberration correction provides the higher resolution for imaging the nanoparticle lattice. Perhaps surprisingly we show that zeolites damage preferentially by ionization effects (radiolysis). The current literature suggests that below incident energies of 40 kV the damage is mainly radiolitic, whereas at incident energies above 200 kV the knock-on damage and material sputtering will be the dominant effect. Our experimental observations support this conclusion and the effects we have observed at 40 kV are not indicative of knock-on damage. Other nanoscale materials such as thin silicon nanowires also benefit from lower voltage imaging. LVHREM imaging provides an excellent option to avoid beam damage to nanowires; our results suggest that LVHREM is suitable for nanowire-biological composites. Our experimental observations serve as a clear demonstration that even at 40 keV accelerating voltage, LVHREM can be used without inducing beam damage to locate dislocations and other crystalline defects, which may have adverse effects on nanowire device performance. Low voltage operation will likely
Institute of Scientific and Technical Information of China (English)
廖小东; 郑思孝; 刘仲阳; 孙官清; 王培录
2001-01-01
The hitches for a ppearing in the high voltage power at 250kV and improvement of the controlling circuit techniques are described. The static high voltage output was exercised by raising the high voltage gradually. The affects between the current load-variety and the vaviety of the input voltoge at + 1096 against the high voltage stability have been obtained. The experiments prove that the high voltage stability have been raised greatly via improving the controlling circuit.
Institute of Scientific and Technical Information of China (English)
张学义; 史立伟
2011-01-01
Nd-Fe-B permanent-magnet rotor is used in a 42V automotive generator. The theory of voltage stability for the permanent-magnet rotor generator is expounded with the relation of armature-reaction reactance, winding leakage reactance and load terminal voltage versus generator speed analyzed. A voltage stabilizer with five-phase semi-control bridge rectification is developed, which integrates the functions of voltage stabilization and current rectification and is composed of reference circuit, comparator circuit, trigger circuit and rectifier circuit. With the voltage stabilizer, the problem of output voltage instability in 42 V permanent-magnet generator at wide ranges of speed and load of vehicle is solved.%在汽车42V发电机中采用钕铁硼永磁转子.阐述了该永磁发电机的稳压原理,分析了其电枢反应电抗、绕组漏抗和负载端压与发电机转速的关系.研制出了集稳压、整流于一体和由基准电路、比较电路、触发电路和整流电路集成的五相半控桥式整流稳压器,解决了汽车用42V永磁发电机在宽转速、宽负载范围内输出电压不稳定的问题.
Ni, YX; Wu, FF; Shi, LB; Zhou, HF; Tam, PTC; Chang, NC; Su, JF; Du, ZB
2005-01-01
This is the second part in a two-part paper on the development of a voltage stability constrained security assessment system (VSC-SAS). In this part, overall VSC-SAS structure and function design and technology used will be presented. The system is expected to be used in both on-line and off-line modes. In on-line mode, on-line SCADA/EMS data will be used for VSC-SAS use; while in off-line mode (usually day-ahead calculation), historical data can be used for VSC-SAS. Both results (i.e. system...
Influence of bias voltage on the stability of CsI photocathodes exposed to air
Nitti, M A; Nappi, E; Singh, B K; Valentini, A
2002-01-01
We describe a possible correlation between the bias voltage applied to the substrate during the growth of CsI photocathodes and the variation of quantum efficiency (QE) after one day exposure to humid air. It was found that fresh samples are much less sensitive to humid air when a high negative bias voltage was applied during film growth. A model based on surface film interaction with water molecules is presented for the observed effect. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements have been performed to examine, respectively, the bulk structure and the surface of fresh and exposed CsI samples. Also reported are transmittance measurements for fresh and aged CsI samples in the wavelength range 190-850 nm.
A heuristic solution for the stability problem in conventional submarines
Directory of Open Access Journals (Sweden)
M. Sinclair
2003-12-01
Full Text Available Seafaring vessels must meet a few very obvious conditions in order to be of any use. The one condition is that they should stay afloat when loaded. The other condition is that they should float upright and with a level keel. The technical terms for these conditions are gravitational stability and trim. In practice some very precise numerical values are calculated for certain parameters in order to describe these conditions. After each refit of a submarine, the numerical values for the parameters referred to above must be recalculated. In the conventional submarines used by the South African Navy these new values must then be translated into the physical redistribution of weights housed in bays in the keel of the submarine. This paper discusses the problem of how this redistribution must be done in order to minimise the amount of work necessary. A heuristic algorithm is proposed by means of which a satisfactory redistribution may economically be computed.
Thermal stability of radiating fluids: The scattering problem
Bakan, Stephan
1984-12-01
The problem of convective instability of a radiating fluid layer with scattering is treated with an extension of the Eddington aproximation that allows the inclusion of anisotropic scattering into the solution of the radiative transfer equation. Introduction of scattering by keeping the optical depth of absorption constant reduces the critical Rayleigh number as well as the wavenumber, and thus, reduces the stabilizing influence of thermal radiation. It is shown that in cases of a narrow radiative boundary layer with a large temperature gradient, higher-order expansion terms are sometimes necessary to approximate the solution properly. In certain cases a two layer convection mode with a large critical wavenumber up to 50 sets in the first layer has two cells developing in and near the two radiative boundary layers.
DEFF Research Database (Denmark)
Zhao, Zhuoli; Yang, Ping; Guerrero, Josep M.
2016-01-01
In this paper, an islanded medium-voltage (MV) microgrid placed in Dongao Island is presented, which integrates renewable-energy-based distributed generations (DGs), energy storage system (ESS), and local loads. In an isolated microgrid without connection to the main grid to support the frequency...... of Zone B. Theoretical analysis, time-domain simulation and field test results under various conditions and scenarios in the Dongao Island microgrid are presented to prove the validity of the introduced control strategy....
Stability of Conductive Carbon Additives for High-voltage Li-ion Battery Cathodes
Nilssen, Benedicte Eikeland
2014-01-01
Conductive carbon additives are important constituents of the current state-of-the-art Li-ion battery cathodes, as the traditional active cathode materials are characterized by too low electronic conductivities. In high-voltage Li-ion batteries, these additives are subject for anion intercalation and electrolyte oxidation, which might cause changes in the conductive carbon network in the cathode, and hence the overall cycling performance of the electrode. This thesis has focused on study the ...
Directory of Open Access Journals (Sweden)
Islam Youcef DJILANI KOBIBI
2014-02-01
Full Text Available With the increase in power demand, operation and planning of large interconnected power system are becoming more complex, so power system will become less secure and stable. A new concept of Flexible AC Transmission system (FACTS brought radical changes in the power system operation and control. FACTS controllers narrow the gap between the no controlled and the controlled power system mode of operation, by providing additional degrees of freedom to control power flows and voltages. Unified Power Flow Controller (UPFC is a versatile FACTS device which can independently or simultaneously control the active power, the reactive power, and the bus voltage to which it is connected. The main purpose of this paper is to identify the optimal location of the Unified Power Flow Controller (UPFC in order to minimize active power losses and improve the voltage profiles using the injection model of the (UPFC in Newton-Raphson load flow algorithm, in an IEEE- 14, 30, 57, 118, 300 Bus test systems.
Stability Estimates for ℎ- Spectral Element Methods for Elliptic Problems
Indian Academy of Sciences (India)
Pravir Dutt; Satyendra Tomar; B V Rathish Kumar
2002-11-01
In a series of papers of which this is the first we study how to solve elliptic problems on polygonal domains using spectral methods on parallel computers. To overcome the singularities that arise in a neighborhood of the corners we use a geometrical mesh. With this mesh we seek a solution which minimizes a weighted squared norm of the residuals in the partial differential equation and a fractional Sobolev norm of the residuals in the boundary conditions and enforce continuity by adding a term which measures the jump in the function and its derivatives at inter-element boundaries, in an appropriate fractional Sobolev norm, to the functional being minimized. Since the second derivatives of the actual solution are not square integrable in a neighborhood of the corners we have to multiply the residuals in the partial differential equation by an appropriate power of $r_k$, where $r_k$ measures the distance between the point and the vertex $A_k$ in a sectoral neighborhood of each of these vertices. In each of these sectoral neighborhoods we use a local coordinate system $(_k, _k)$ where $_k = ln r_k$ and $(r_k, _k)$ are polar coordinates with origin at $A_k$, as first proposed by Kondratiev. We then derive differentiability estimates with respect to these new variables and a stability estimate for the functional we minimize. In [6] we will show that we can use the stability estimate to obtain parallel preconditioners and error estimates for the solution of the minimization problem which are nearly optimal as the condition number of the preconditioned system is polylogarithmic in , the number of processors and the number of degrees of freedom in each variable on each element. Moreover if the data is analytic then the error is exponentially small in .
Energy Technology Data Exchange (ETDEWEB)
Sahmani, Saeid; Bahrami, Mohsen [Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)
2015-01-15
In the current paper, dynamic stability analysis of microbeams subjected to piezoelectric voltage is presented in which the microbeam is integrated with piezoelectric layers on the lower and upper surfaces. Both of the flutter and divergence instabilities of microbeams with clamped-clamped and clamped-free boundary conditions are predicted corresponding to various values of applied voltage. To take size effect into account, the classical Timoshenko beam theory in conjunction with strain gradient elasticity theory is utilized to develop nonclassical beam model containing three additional internal length scale parameters. By using Hamilton's principle, the higher-order governing differential equations and associated boundary conditions are derived. Afterward, generalized differential quadrature method is employed to discretize the size-dependent governing differential equations along with clamped-clamped and clamped-free end supports. The critical piezoelectric voltages corresponding to various values dimensionless length scale parameter are evaluated and compared with those predicted by the classical beam theory. It is revealed that in the case of clamped-free boundary conditions, the both of flutter and divergence instabilities occur. However, for the clamped-clamped microbeams, only divergence instability takes place.
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
A new approach to determining the local boundaries of voltage stability region in power injection space (IVSR) for power system with wind farms is presented. It can be used for power system voltage stability analysis and on-line security assessment with considering the output uncertainty of the wind farms. Firstly, power flow tracing and double dispatching are used to determine the generators that are closely related to the wind farms, in order to balance the power fluctuations caused by the wind speed variation. Then, modal analysis is used to get the key generators to achieve an effective dimension reduction for IVSR. Finally, the forecasting output power (or wind speed) of wind farms is divided into several intervals. For each interval, the corresponding local IVSR boundaries can be calculated by the method based on small disturbance. Moreover, parallel process is used to accelerate the computing speed. The presented approach is validated by several power systems. It can be revealed that the approach can give the local IVSR boundaries at different wind speeds and has a good engineering application prospect.
Theory and calculation of two-stage voltage stabilizer on zener diodes
Directory of Open Access Journals (Sweden)
G. S. Veksler
1966-12-01
Full Text Available Two-stage stabilizer is compared with one-stage. There have been got formulas, which give the possibility to make an engineering calculation. There is an example of the calculation.
Wagner, Ralf; Korth, Martin; Streipert, Benjamin; Kasnatscheew, Johannes; Gallus, Dennis R; Brox, Sebastian; Amereller, Marius; Cekic-Laskovic, Isidora; Winter, Martin
2016-11-16
Diverse LiPF6 hydrolysis products evolve during lithium-ion battery cell operation at elevated operation temperatures and high operation voltages. However, their impact on the formation and stability of the electrode/electrolyte interfaces is not yet investigated and understood. In this work, literature-known hydrolysis products of LiPF6 dimethyl fluorophosphate (DMFP) and diethyl fluorophosphate (DEFP) were synthesized and characterized. The use of DMFP and DEFP as electrolyte additive in 1 M LiPF6 in EC:EMC (1:1, by wt) was investigated in LiNi1/3Mn1/3Co1/3O2/Li half cells. When charged to a cutoff potential of 4.6 V vs Li/Li(+), the additive containing cells showed improved cycling stability, increased Coulombic efficiencies, and prolonged shelf life. Furthermore, low amounts (1 wt % in this study) of the aforementioned additives did not show any negative effect on the cycling stability of graphite/Li half cells. DMFP and DEFP are susceptible to oxidation and contribute to the formation of an effective cathode/electrolyte interphase as confirmed by means of electrochemical stability window determination, and X-ray photoelectron spectroscopy characterization of pristine and cycled electrodes, and they are supported by computational calculations.
Wind farms generation limits and its impact in real-time voltage stability assessment
DEFF Research Database (Denmark)
Perez, Angel; Jóhannsson, Hjörtur; Østergaard, Jacob
2015-01-01
indicates the distance to the limit activation and theeffect of each load in such a limit. The wind farm control schemesincludes voltage control and it is represented as a constantcurrent at its limit. A criteria to select the critical bus bar, basedon the generator transformation coefficients, is presented....... Thismethodology is tested in a platform that produces synthesizedPMU measurements from time-domain simulations and criticalboundary for the wind-farm limits are shown. The methodology isalso tested for synchronous machines and its parallel structure isexploited when implemented in a High Performance...
Institute of Scientific and Technical Information of China (English)
吴丽娜; 邵龙; 刘观起; 陶善宏
2014-01-01
ABSTRACT:To deal with the problem of transient voltage stability in the power system integrated with large-scale wind farms,this paper discusses the mechanism of transient voltage instability and the analysis method of transient voltage stability. Meanwhile,it introduces two important reactive power compen-sation devices that are SVC and STATCOM. The BPA software is used for the simulation analysis of an actual national power grid. The results show that wind speed variation and system short-circuit fault can affect transient voltage stability of power system,resulting in a reduction of the system voltage level. Both SVC and STATCOM can give support to the system voltage, and the support effect of STATCOM is more obvious.%针对大规模风电并网后系统的暂态电压稳定性问题，阐述了暂态电压失稳的机理以及暂态电压稳定性的分析计算方法，介绍了2种重要的无功补偿装置SVC和STATCOM。采用BPA软件对国内某一实际电网进行了仿真分析，结果表明，风速变化和系统发生短路故障均会对系统的暂态电压稳定性造成影响，导致系统的电压水平降低。装设SVC或STATCOM对系统电压均有支撑作用，且STATCOM对电压的支撑作用更加明显。
基于Multisim10仿真软件的多输出直流稳压电源设计%Design of Multi-Output DC Stabilized Voltage Supply Based on Multisim10
Institute of Scientific and Technical Information of China (English)
刘磊; 胡海燕; 李伟达; 李娟; 秦佳
2013-01-01
提出了一种多输出线性直流稳压电源的设计，以固定式集成稳压器为核心，可以提供多个固定的直流电压输出。使用EDA软件平台Multisim10对电源设计过程进行仿真分析，针对仿真过程中发现的问题提出解决方案，提高了实验效率。经对电源样机的实验测试，该电源性能良好、工作可靠，输出电压和输出电流、稳压系数和纹波电压均满足设计要求，可以满足实验设备对多种直流电的需要。%This paper raised design of a kind of linear multi-output direct current (DC) stabilized voltage supply, which was based on ifxed type stabilized voltage integrated circuits (ICs), providing multiple ifxed DC voltage outputs. EDA software platform, Multisim 10 was used to simulate and analyze the design process of power supply. In allusion to problems in simulation process, this paper raised settling plan to improve the efifciency of the experiment. The test for the prototype has proved that this type of power supply is good in performance, reliable in work, meeting the design requirements of output voltage, output current, stabilized voltage coefifcient and output ripple voltage, as well as multi-DC requirements for experimental equipment.
Suter, Marc R; Kirschmann, Guylène; Laedermann, Cedric J; Abriel, Hugues; Decosterd, Isabelle
2013-01-01
Voltage-gated sodium channels dysregulation is important for hyperexcitability leading to pain persistence. Sodium channel blockers currently used to treat neuropathic pain are poorly tolerated. Getting new molecules to clinical use is laborious. We here propose a drug already marketed as anticonvulsant, rufinamide. We compared the behavioral effect of rufinamide to amitriptyline using the Spared Nerve Injury neuropathic pain model in mice. We compared the effect of rufinamide on sodium currents using in vitro patch clamp in cells expressing the voltage-gated sodium channel Nav1.7 isoform and on dissociated dorsal root ganglion neurons to amitriptyline and mexiletine. In naive mice, amitriptyline (20 mg/kg) increased withdrawal threshold to mechanical stimulation from 1.3 (0.6-1.9) (median [95% CI]) to 2.3 g (2.2-2.5) and latency of withdrawal to heat stimulation from 13.1 (10.4-15.5) to 30.0 s (21.8-31.9), whereas rufinamide had no effect. Rufinamide and amitriptyline alleviated injury-induced mechanical allodynia for 4 h (maximal effect: 0.10 ± 0.03 g (mean ± SD) to 1.99 ± 0.26 g for rufinamide and 0.25 ± 0.22 g to 1.92 ± 0.85 g for amitriptyline). All drugs reduced peak current and stabilized the inactivated state of voltage-gated sodium channel Nav1.7, with similar effects in dorsal root ganglion neurons. At doses alleviating neuropathic pain, amitriptyline showed alteration of behavioral response possibly related to either alteration of basal pain sensitivity or sedative effect or both. Side-effects and drug tolerance/compliance are major problems with drugs such as amitriptyline. Rufinamide seems to have a better tolerability profile and could be a new alternative to explore for the treatment of neuropathic pain.
Driving CZTS to the SQ Limit: Solving the Open Circuit Voltage Problem
Energy Technology Data Exchange (ETDEWEB)
Haight, Richard A. [IBM Research, Yorktown, NY (United States). Thomas J. Watson Research Center; McCandless, Brian E. [Univ. of Delaware, Newark, DE (United States); Kummel, Andrew C. [Univ. of California, San Diego, CA (United States); Gordon, Roy G. [Harvard Univ., Cambridge, MA (United States)
2016-12-15
A key objective of this 3 year research effort was to reduce the open circuit voltage (Voc) deficit, defined as the difference between the absorber band gap and the measured Voc to below 475mV from values at the beginning of this work of 630-730mV. To achieve this reduction, along with the attendant goals of higher Voc and efficiency, detailed studies into the fundamental understanding of existing limitations were undertaken.
A SURVEY: PID OPTIMIZATION FOR AUTOMATIC VOLTAGE REGULATOR
Ajay Dixit*, Miss.Pragati Joshi, Mr.Mahesh Lokhande
2016-01-01
This paper presents on survey paper of PSO and automatic voltage regulator for synchronous generator. It is used to obtain for regulation and stability of any electrical equipment. There are many technology/methods were used in automatic voltage regulator as well as different controller used for improving robustness, overshoot, rise time and voltage control but problem is about to survey on Automatic Voltage Regulator. Comparisons studies which are based on PID Controller are performed to sh...
电力系统电压稳定分析方法综述%Summary of Power System’ s Voltage Stability Analysis Method
Institute of Scientific and Technical Information of China (English)
刘迎迎; 孙毅; 李昕; 陈维伟
2013-01-01
This paper studies the definition and classification of voltage stability,introduce static and dynamic analysis method of voltage stability so far with a comprehensive analysis of voltage stability analysis method. The static analysis method include singular value decomposition method, the sensitivity method, the continu-ous power flow method and the collapse point method;the dynamic analysis method include Small perturbation analysis, time-domain simulation method, energy function method and bifurcation theory. And comprehen-sively analyze and evaluate analysis method of voltage stability. we summarize the feature of voltage stability a-nalysis method and look into the future development direction.%详细研究了电压稳定的定义及分类，介绍了静态电压稳定和动态电压稳定分析方法。静态电压稳定分析法包括奇异值分解法、灵敏度法、连续潮流法、崩溃点法；动态电压稳定分析法包括小扰动分析法、时域仿真法、能量函数法和分岔理论。对电压稳定分析方法进行了综合分析和评价，总结了各类分析方法的特点并展望了未来发展方向。
Mustafa, Ghullam; Bak-Jensen, Birgitte; Mahat, Pukar; Cecati, Carlo
2013-01-01
Any problem with voltage in a power network is undesirable as it aggravates the quality of the power. Power electronic devices such as Voltage Source Converter (VSC) based Static Synchronous Compensator (STATCOM) etc. can be used to mitigate the voltage problems in the distribution system. The voltage problems dealt with in this paper are to show how to mitigate unbalanced voltage sags and voltage unbalance in the CIGRE Low Voltage (LV) test network and net-works like this. The voltage unbala...
DEFF Research Database (Denmark)
Kwon, Jun Bum; Wang, Xiongfei; Bak, Claus Leth;
2015-01-01
As the increasing of power electronics based systems, not only the component-based analysis but also a systematic interaction analysis with each other systems are being important. Especially studies about the stability and the harmonics interaction are critical in order to establish the required ...
Analysis of stability problems via matrix Lyapunov functions
Directory of Open Access Journals (Sweden)
Anatoly A. Martynyuk
1990-01-01
Full Text Available The stability of nonlinear systems is analyzed by the direct Lyapunov's method in terms of Lyapunov matrix functions. The given paper surveys the main theorems on stability, asymptotic stability and nonstability. They are applied to systems of nonlinear equations, singularly-perturbed systems and hybrid systems. The results are demonstrated by an example of a two-component system.
Felix, Ricardo; Calderón-Rivera, Aida; Andrade, Arturo
2013-09-01
Voltage-gated Ca(2+) (CaV) channels mediate Ca(2+) ions influx into cells in response to depolarization of the plasma membrane. They are responsible for initiation of excitation-contraction and excitation-secretion coupling, and the Ca(2+) that enters cells through this pathway is also important in the regulation of protein phosphorylation, gene transcription, and many other intracellular events. Initial electrophysiological studies divided CaV channels into low-voltage-activated (LVA) and high-voltage-activated (HVA) channels. The HVA CaV channels were further subdivided into L, N, P/Q, and R-types which are oligomeric protein complexes composed of an ion-conducting CaVα1 subunit and auxiliary CaVα2δ, CaVβ, and CaVγ subunits. The functional consequences of the auxiliary subunits include altered functional and pharmacological properties of the channels as well as increased current densities. The latter observation suggests an important role of the auxiliary subunits in membrane trafficking of the CaVα1 subunit. This includes the mechanisms by which CaV channels are targeted to the plasma membrane and to appropriate regions within a given cell. Likewise, the auxiliary subunits seem to participate in the mechanisms that remove CaV channels from the plasma membrane for recycling and/or degradation. Diverse studies have provided important clues to the molecular mechanisms involved in the regulation of CaV channels by the auxiliary subunits, and the roles that these proteins could possibly play in channel targeting and membrane Stabilization.
Research on the voltage stability in wind power genenation%含风电场的系统电压稳定性研究
Institute of Scientific and Technical Information of China (English)
姚刚; 彭志炜
2011-01-01
The equivalent of wind model including DFIG and the methods for analyzing transient voltage stability are introduced. The voltage stability of system with wind farms is analyzed from the static and the transient. The influence factors are pointed out, which pointed out the direction of voltage stability improvement in power system.%介绍了含DFIG的风电场模型的等值以及电压稳定性分析的方法，分别从静态和暂态方面分析了含风电场的系统电压稳定性，并指出了影响因素，为改善系统电压稳定性指出了方向。
Proposal of indexes for fast voltage stability evaluation of ac/dc transmission systems
Directory of Open Access Journals (Sweden)
Jorge Wilson González
2011-01-01
Full Text Available En este artículo se desarrolla un análisis de estabilidad de tensión de sistemas ca/cd empleando indicadores estáticos y modales. Se propone un tratamiento novedoso para indicadores de estabilidad de tensión, con el fin de obtener una mayor información sobre los requerimientos en redes de variadas fortalezas, en términos de la estabilidad de tensión. El nuevo tratamiento se ofrece como un medio para prevenir potenciales problemas en redes de transmisión de corriente directa, High Voltage dc Transmission Systems (HVdc, conectados a nodos débiles. Los indicadores son convertidos a por unidad y comparados en diferentes relaciones de corto circuito, Short Circuit Ratios (SCR, en una red modificada tipo IEEE de 14 barras, la cual posee un sistema HVdc conectado en su barra más débil. Los alcances pueden servir tanto para planeamiento como para monitoreo en tiempo real de la estabilidad de tensión en sistemas eléctricos de potencia incluyendo nodos ca/cd.
Analysis of the match problem of a capacitive voltage divider with a long measurement cable
Yu, Bin-Xiong; Li, Rui; Su, Jian-Cang; Zhao, Liang; Zhang, Yu; Zheng, Lei; Zeng, Bo; Cheng, Jie; Gao, Peng-Cheng; Qiu, Xu-Dong; Xu, Xu-dong
2017-09-01
Research is carried out on the basis of the traditional two-end matched circuit of a capacitive voltage divider with a long measurement cable. Transmission progress in the circuit is analyzed theoretically. A match condition of the circuit is acquired, which requires that the circuit satisfies two conditions: (1) the measurement error should be small for a pulse with a duration of less than twice the delay time of the measurement cable; (2) the initial division ratio and the stable division ratio of the circuit are the same. Two matched methods of the circuit are acquired, including the first-order matched method and the second-order matched method. Numerical simulations are carried out. According to the simulation results, the relative errors of the circuits with a cable of 20 m are less than 1.5%, obtained by using both match methods for measurement of rectangular pulses with rise and fall times of 5 ns. An improved circuit is presented, which is suitable for any situation where the low-voltage capacitance of the capacitive divider is even smaller than the capaictance of the measurement cable. A verification experment is carried out, and the test result confirms the simulation result.
Lidocaine stabilizes the open state of CNS voltage-dependent sodium channels.
Castañeda-Castellanos, David R; Nikonorov, Igor; Kallen, Roland G; Recio-Pinto, E
2002-03-28
We have previously reported that the lidocaine action is different between CNS and muscle batrachotoxin-modified Na+ channels [Salazar et al., J. Gen. Physiol. 107 (1996) 743-754; Brain Res. 699 (1995) 305-314]. In this study we examined lidocaine action on CNS Na+ currents, to investigate the mechanism of lidocaine action on this channel isoform and to compare it with that proposed for muscle Na+ currents. Na+ currents were measured with the whole cell voltage clamp configuration in stably transfected cells expressing the brain alpha-subunit (type IIA) by itself (alpha-brain) or together with the brain beta(1)-subunit (alphabeta(1)-brain), or the cardiac alpha-subunit (hH1) (alpha-cardiac). Lidocaine (100 microM) produced comparable levels of Na+ current block at positive potentials and of hyperpolarizing shift of the steady-state inactivation curve in alpha-brain and alphabeta(1)-brain Na+ currents. Lidocaine accelerated the rates of activation and inactivation, produced an hyperpolarizing shift in the steady-state activation curve and increased the current magnitude at negative potentials in alpha-brain but not in alphabeta(1)-brain Na+ currents. The lidocaine action in alphabeta(1)-brain resembled that observed in alpha-cardiac Na+ currents. The lidocaine-induced increase in current magnitude at negative potentials and the hyperpolarizing shift in the steady-state activation curve of alpha-brain, are novel effects and suggest that lidocaine treatment does not always lead to current reduction/block when it interacts with Na+ channels. The data are explained by using a modified version of the model proposed by Vedantham and Cannon [J. Gen. Physiol., 113 (1999) 7-16] in which we postulate that the difference in lidocaine action between alpha-brain and alphabeta(1)-brain Na+ currents could be explained by differences in the lidocaine action on the open channel state.
International Seminar on Stability Problems for Stochastic Models
Zolatarev, Vladimir
1993-01-01
The subject of this book is a new direction in the field of probability theory and mathematical statistics which can be called "stability theory": it deals with evaluating the effects of perturbing initial probabilistic models and embraces quite varied subtopics: limit theorems, queueing models, statistical inference, probability metrics, etc. The contributions are original research articles developing new ideas and methods of stability analysis.
线性直流稳压电源实验分析%Experimental Analysis of Linear DC Stabilized Voltage Power Supply
Institute of Scientific and Technical Information of China (English)
唐红
2012-01-01
Stabilized voltage power supply is a important chapter of analog electronics technology course. In the course of teaching practice activities about linear DC stabilized voltage power supply, some phenomenon that test data is not accurate and components are burnt out often turn up. As a result, it is important to master circuit philosophy and test method of stabilized voltage power supply. Students can be familiar with stabilized vohage power supply which is made up of single phase bridge rectifier, capacitor filter and integration of the three terminal regulator and the method to test each technical indication of stabilized voltage power supply.%稳压电源是模拟电子技术课程中重要的章节,在线性直流稳压电源教学实验活动中,常会出现测试数据不准、烧坏元器件等现象,因此掌握稳压电源的电路原理及测试方法极为重要。通过线性稳压电源实验,使学生熟悉由单相桥式整流、电容滤波和集成三端稳压器组成的直流稳压电源;熟悉稳压电源各项技术指标的测量方法。
An Analysis on Security Control of Voltage Stability in Power System%电力系统电压稳定的安全控制
Institute of Scientific and Technical Information of China (English)
纳生成
2015-01-01
电力系统电压稳定的安全控制工作非常重要,影响电力系统电压稳定的因素包括电压调节能力、电力系统负荷特点、输电线路电力稳定限度等,在实际工作中,要积极提高电网工作人员的专业素质,进一步提高电力系统输电线路的设计水平,建立健全对电压安全进行监控和调节的制度,以确保电力系统的电压保持稳定运行的状态.%Security control on voltage stability in power system is very important,factors impact the voltage stability of power system includes voltage regulation capacity,loading characteristics of power system,the limit of electric stability of transmission line.In practical operation,it is necessary to improve the professional quality of personnel,further improve the design level of transmission line of the power system,establish and improve system to supervise and control the security of voltage,so as to ensure the voltage of the power system in a stable working environment.
(r,s)-STABILITY OF UNFOLDING OF Γ-EQUIVARIANT BIFURCATION PROBLEM
Institute of Scientific and Technical Information of China (English)
Liu Hengxing; Zhang Dunmu
2005-01-01
In this paper,the Γ-equivariant (s, t)-equivalence relation and Γ-equivariant infinitesimally (r, s)-stability of Γ-equivariant bifurcation problem are defined. The criterion for Γ-equivariant infinitesimally (r, s)-stability is proven when Γ is a compact finite Lie group . Transversality condition is used to characterize the stability.
STABILIZED NUMERICAL APPROXIMATIONS OF THE BACKWARD PROBLEM OF A PARABOLIC EQUATION
Institute of Scientific and Technical Information of China (English)
韩厚德; 胡刚
2001-01-01
In this paper, the backward problem ora parabolic equation is considered. Three new stability estimates are given. Based on the new stability estimates, a regularization method is proposed for which error estimates are available. The regularization method can be used for the numerical approximations of the original problem which will be shown by the numerical examples.
Orbital stability of the restricted three body problem in General Relativity
2015-01-01
We consider the problem of orbital stability of the motion of a test particle in the restricted three-body problem, by using the orbital moment and its time derivative. We show that it is possible to get some insight into the stability properties of the motion of test particles, without knowing the exact solutions of the motion equations.
Orbital stability of the restricted three-body problem in General Relativity
Abishev, M.; Quevedo, H.; Toktarbay, S.; Zhami, B.
We consider the problem of orbital stability of the motion of a test particle in the restricted three-body problem, by using the orbital moment and its time derivative. We show that it is possible to get some insight into the stability properties of the motion of test particles, without knowing the exact solutions of the motion equations.
Orbital stability of the restricted three body problem in General Relativity
Abishev, M; Toktarbay, S; Zhami, B
2015-01-01
We consider the problem of orbital stability of the motion of a test particle in the restricted three-body problem, by using the orbital moment and its time derivative. We show that it is possible to get some insight into the stability properties of the motion of test particles, without knowing the exact solutions of the motion equations.
Existence and Stability of Solutions for Implicit Multivalued Vector Equilibrium Problems
Directory of Open Access Journals (Sweden)
Li Qiuying
2011-01-01
Full Text Available A class of implicit multivalued vector equilibrium problems is studied. By using the generalized Fan-Browder fixed point theorem, some existence results of solutions for the implicit multivalued vector equilibrium problems are obtained under some suitable assumptions. Moreover, a stability result of solutions for the implicit multivalued vector equilibrium problems is derived. These results extend and unify some recent results for implicit vector equilibrium problems, multivalued vector variational inequality problems, and vector variational inequality problems.
Using SVC to Improve Dynamic Voltage Stability of Regional Power Grid%用SVC提高区域电网的动态电压稳定性
Institute of Scientific and Technical Information of China (English)
唐莉
2011-01-01
The differences between power stability and frequency stability are analyzed. The necessity of regional maintains voltage stability is proposed. Under two conditions that reactive power compensator for the capacitors and SVC, the dynamic process of regional power grid voltage after large disturbances are simulated. The results show that using SVC can significantly improve the dynamic voltage stability of the regional power grid. The effects of SVC regulator time constant on dynamic process of voltage change are discussed.%分析电压稳定性与频率稳定性的不同,提出分区保持电压稳定性的必要性。仿真计算了无功补偿器为电容器和SVC两种情况下区域电网发生大干扰后电压变化的动态过程,说明采用SVC可以显著提高区域电网的动态电压稳定性,并探讨SVC调节的时间常数对电压变化的动态过程的影响。
Energy Technology Data Exchange (ETDEWEB)
Aromataris, Luis [Universidad Nacional de Rio Cuarto (UNRC) (Argentina); Arnera, Patricia; Riubrugent, Jean [Universidad Nacional de La Plata, Buenos Aires (Argentina). Facultad de Ingenieria. Instituto de Investigaciones Tecnologicas para Redes y Equipos Electricos
2001-07-01
This work investigate the impact produced by the load model on the voltage stability analysis of an electric system. Qualitative and quantitative analyses are approached in connection with the effects of modeling the electric loads by both dynamical and static way. Also it is highlighted the importance of using dynamical models of load, mainly when it is composed by motors.
Hybrid Impedance Network-Based Converter With High Voltage Gain and No Commutation Problem
DEFF Research Database (Denmark)
Mostaan, Ali; N. Soltani, Mohsen; A. Gorji, Saman
2016-01-01
In this paper, a new hybrid converter based on Z-source DC/DC converter with common ground is introduced. The proposed converter can supply ac and dc loads simultaneously or individually (stand- alone ac or dc loads). Also, the commutation problem of its counterpart has been solved in this topolo...
Stabilization meshless method for convection-dominated problems
Institute of Scientific and Technical Information of China (English)
ZHANG Xiao-hua; OUYANG Jie; WANG Jian-yu
2008-01-01
It is well-known that the standard Galerkin is not ideally suited to deal with the spatial discretization of convection-dominated problems. In this paper, several tech- niques are proposed to overcome the instability issues in convection-dominated problems in the simulation with a meshless method. These stable techniques included nodal re- finement, enlargement of the nodal influence domain, full upwind meshless technique and adaptive upwind meshless technique. Numerical results for sample problems show that these techniques are effective in solving convection-dominated problems, and the adaptive upwind meshless technique is the most effective method of all.
CISM International Advanced School on Stability Problems of Steel Structures
Skaloud, M
1992-01-01
This volume strives to give complete information about the main aspect of the stability behaviour of steel structures and their members. In following this objective, the volume presents a complete scientific background (profiting from the fact that the authors of the individual parts of the publication have personally been very active in the corresponding field of research for an extended period of time now), but also establishes recommendations, procedures and formulae for practical design. The significance of the volume may be seen in its challenging current concepts of stability analysis, encouraging progress in the field and thereby establishing an advanced basis for more reliable and economical design.
Optimal stability polynomials for numerical integration of initial value problems
Ketcheson, David I.
2013-01-08
We consider the problem of finding optimally stable polynomial approximations to the exponential for application to one-step integration of initial value ordinary and partial differential equations. The objective is to find the largest stable step size and corresponding method for a given problem when the spectrum of the initial value problem is known. The problem is expressed in terms of a general least deviation feasibility problem. Its solution is obtained by a new fast, accurate, and robust algorithm based on convex optimization techniques. Global convergence of the algorithm is proven in the case that the order of approximation is one and in the case that the spectrum encloses a starlike region. Examples demonstrate the effectiveness of the proposed algorithm even when these conditions are not satisfied.
Solution to the Generalized Champagne Problem on simultaneous stabilization of linear systems
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The well-known Generalized Champagne Problem on simultaneous stabilization of linear systems is solved by using complex analysis and Blondel's technique. We give a complete answer to the open problem proposed by Patel et al., which automatically includes the solution to the original Champagne Problem. Based on the recent development in automated inequality-type theorem proving, a new stabilizing controller design method is established. Our numerical examples significantly improve the relevant results in the literature.
Chaudhary, Bhumika; Kulkarni, Ashish; Jena, Ajay Kumar; Ikegami, Masashi; Udagawa, Yosuke; Kunugita, Hideyuki; Ema, Kazuhiro; Miyasaka, Tsutomu
2017-06-09
It is well known that the surface trap states and electronic disorders in the solution-processed CH3 NH3 PbI3 perovskite film affect the solar cell performance significantly and moisture sensitivity of photoactive perovskite material limits its practical applications. Herein, we show the surface modification of a perovskite film with a solution-processable hydrophobic polymer (poly(4-vinylpyridine), PVP), which passivates the undercoordinated lead (Pb) atoms (on the surface of perovskite) by its pyridine Lewis base side chains and thereby eliminates surface-trap states and non-radiative recombination. Moreover, it acts as an electron barrier between the perovskite and hole-transport layer (HTL) to reduce interfacial charge recombination, which led to improvement in open-circuit voltage (Voc ) by 120 to 160 mV whereas the standard cell fabricated in same conditions showed Voc as low as 0.9 V owing to dominating interfacial recombination processes. Consequently, the power conversion efficiency (PCE) increased by 3 to 5 % in the polymer-modified devices (PCE=15 %) with Voc more than 1.05 V and hysteresis-less J-V curves. Advantageously, hydrophobicity of the polymer chain was found to protect the perovskite surface from moisture and improved stability of the non-encapsulated cells, which retained their device performance up to 30 days of exposure to open atmosphere (50 % humidity). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Energy Technology Data Exchange (ETDEWEB)
Oliveira, Hermes R.P.M. de; Jesus, Nelson C. de; Figueiredo, Carlos E.C. [AES Sul, Porto Alegre, RS (Brazil); Batista, Edson L. [Universidade Regional do Noroeste do Estado do Rio Grande do Sul, Inijui, RS (Brazil); Martinez, Manuel L.B. [Universidade Federal de Itajuba (UNIFEI), MG (Brazil)
2005-12-15
This article presents an analysis and diagnosis related to a typical commercial consumer with problems of energy quality, supplied by low voltage net. In this direction, after the supplied voltage to have been monitored through specific analysers and careful investigations, it was concluded that the origin of disturbances was located in the consumer systems. The main steps used in the analysis and measurements results are described.
Total parenteral nutrition - Problems in compatibility and stability
DEFF Research Database (Denmark)
Schroder, A.M.
2008-01-01
Adding calcium, trace elements and vitamins could turn parenteral nutrition into a dangerous product, which could harm the patient. This article focuses on the major pharmaceutical problems of parenteral. nutrition when adding nutritional compounds Udgivelsesdato: 2008...
Stability analysis of the inverse transmembrane potential problem in electrocardiography
Burger, Martin; Mardal, Kent-André; Nielsen, Bjørn Fredrik
2010-10-01
In this paper we study some mathematical properties of an inverse problem arising in connection with electrocardiograms (ECGs). More specifically, we analyze the possibility for recovering the transmembrane potential in the heart from ECG recordings, a challenge currently investigated by a growing number of groups. Our approach is based on the bidomain model for the electrical activity in the myocardium, and leads to a parameter identification problem for elliptic partial differential equations (PDEs). It turns out that this challenge can be split into two subproblems: the task of recovering the potential at the heart surface from body surface recordings; the problem of computing the transmembrane potential inside the heart from the potential determined at the heart surface. Problem (1), which can be formulated as the Cauchy problem for an elliptic PDE, has been extensively studied and is well known to be severely ill-posed. The main purpose of this paper is to prove that problem (2) is stable and well posed if a suitable prior is available. Moreover, our theoretical findings are illuminated by a series of numerical experiments. Finally, we discuss some aspects of uniqueness related to the anisotropy in the heart.
Control and stability problems of remote orbital capture
Kaplan, M. H.; Nadkarni, A. A.
1977-01-01
Certain space shuttle missions may require retrieval of passive spinning and precessing satellites. One proposed means of retrieval utilizes a free-flying teleoperator launched from the shuttle. A study of misalignment, stability, and certain control aspects during capture of an object is reported here. The approach used is to model the dynamics by a Lagrangian formulation and apply torque components to dissipate motion. Differential angular rates between teleoperator and object are assumed, and control responses after capture are reviewed.
ON RESERVES, STABILITY AND THE MAXIMUM SUSTAINABLE YIELD PROBLEM
Directory of Open Access Journals (Sweden)
Arild Wikan
2013-01-01
Full Text Available Due to the fact that several species of commercial interest have been overexploited throughout the years it is important to understand how harvest and other factors like introducing reserves influence the dynamic behaviour of a population with respect to stability and possible extinction. Therefore, simple one-population models are analysed and it is shown that harvest acts in a strong stabilizing fashion in the sense that it may transfer a population which exhibits chaotic oscillations to a state where the equilibrium population is stable. Moreover, if we divide the habitat of the population into a reserve and a harvest zone we find that increased harvest as well as migration between the two areas act stabilizing but that the former turns out to be the dominating one. If age structure is included in the population model harvest may not necessarily play the same role, especially if the number of age classes become large. Regarding MSY, we demonstrate that it is indeed possible to obtain the same MSY in the case where the habitat is split into a reserve and a harvest zone as in case of no reserve.
Grezes, C.; Rojas Rozas, A.; Ebrahimi, F.; Alzate, J. G.; Cai, X.; Katine, J. A.; Langer, J.; Ocker, B.; Khalili Amiri, P.; Wang, K. L.
2016-07-01
The effect of in-plane magnetic field on switching voltage (Vsw) and thermal stability factor (Δ) are investigated in electric-field-controlled perpendicular magnetic tunnel junctions (p-MTJs). Dwell time measurements are used to determine the voltage dependence of the energy barrier height for various in-plane magnetic fields (Hin), and gain insight into the Hin dependent energy landscape. We find that both Vsw and Δ decrease with increasing Hin, with a dominant linear dependence. The results are reproduced by calculations based on a macrospin model while accounting for the modified magnetization configuration in the presence of an external magnetic field.
Energy Technology Data Exchange (ETDEWEB)
Taubman, Matthew S; Phillips, Mark C
2015-04-07
A method is disclosed for power normalization of spectroscopic signatures obtained from laser based chemical sensors that employs the compliance voltage across a quantum cascade laser device within an external cavity laser. The method obviates the need for a dedicated optical detector used specifically for power normalization purposes. A method is also disclosed that employs the compliance voltage developed across the laser device within an external cavity semiconductor laser to power-stabilize the laser mode of the semiconductor laser by adjusting drive current to the laser such that the output optical power from the external cavity semiconductor laser remains constant.
Fu, Qiang; Zhang, Wan-Rong; Jin, Dong-Yue; Zhao, Yan-Xiao; Wang, Xiao
2016-12-01
The product of the cutoff frequency and breakdown voltage (fT×BVCEO) is an important figure of merit (FOM) to characterize overall performance of heterojunction bipolar transistor (HBT). In this paper, an approach to introducing a thin N+-buried layer into N collector region in silicon-on-insulator (SOI) SiGe HBT to simultaneously improve the FOM of fT×BVCEO and thermal stability is presented by using two-dimensional (2D) numerical simulation through SILVACO device simulator. Firstly, in order to show some disadvantages of the introduction of SOI structure, the effects of SOI insulation layer thickness (TBOX) on fT, BVCEO, and the FOM of fT×BVCEO are presented. The introduction of SOI structure remarkably reduces the electron concentration in collector region near SOI substrate insulation layer, obviously reduces fT, slightly increases BVCEO to some extent, but ultimately degrades the FOM of fT×BVCEO. Although the fT, BVCEO, and the FOM of fT×BVCEO can be improved by increasing SOI insulator SiO2 layer thickness TBOX in SOI structure, the device temperature and collector current are increased due to lower thermal conductivity of SiO2 layer, as a result, the self-heating effect of the device is enhanced, and the thermal stability of the device is degraded. Secondly, in order to alleviate the foregoing problem of low electron concentration in collector region near SOI insulation layer and the thermal stability resulting from thick TBOX, a thin N+-buried layer is introduced into collector region to not only improve the FOM of fT×BVCEO, but also weaken the self-heating effect of the device, thus improving the thermal stability of the device. Furthermore, the effect of the location of the thin N+-buried layer in collector region is investigated in detail. The result show that the FOM of fT×BVCEO is improved and the device temperature decreases as the N+-buried layer shifts toward SOI substrate insulation layer. The approach to introducing a thin N+-buried layer
Institute of Scientific and Technical Information of China (English)
李苏川; 吕智林; 谭颖
2016-01-01
为了深入研究孤立微网的静态电压稳定性问题，将分岔理论应用于微网静态电压稳定性分析研究。以鞍结分岔点作为电压稳定临界点，采用连续潮流( CPF)算法对四节点小型孤立微网进行电压稳定性分析，追踪出该系统的PU曲线，并根据特征根来判断该曲线上是否存在鞍结分岔点。分别计算出含SVC和不含SVC系统的电压稳定极限，得出负荷节点处电压稳定裕度。由实验结果可以看出，随着负荷参数的不断增大，负荷所需功率和发电机的输出功率也会随之增大，当达到它的传输极限时就会产生鞍结分岔现象，从而导致系统电压出现跌落甚至崩溃的现象。结果表明，利用上述方法可以有效地计算出孤立微网的电压稳定极限，并且使用SVC控制器可以提高系统电压稳定性。%In order to study the problem of static voltage stability of isolated micro-grid, the bifurca-tion theory is applied. The saddle node bifurcation point is used as the voltage collapse critical point while using continuous power flow ( CPF) algorithm to analyze the voltage stability of a small isolated micro-grid with four nodes. Then by tracing the PU curve of the system and according to the charac-teristics of the root the saddle node bifurcation point in the curve is determined. The stability limit of the SVC and non SVC system voltage are calculated respectively to obtain the voltage stability margin of load node. The experiments show that with the increase of the load parameters, the required pow-er of the load and the output power of the generator will increase. Then the saddle node bifurcation will occur when the transmission limit which causes the system voltage to fall or collapse. The results of simulations show that the voltage stability limit of isolated micro grid can be calculated by using this method. And by using SVC controller the stability of system voltage can be improved.
Energy Technology Data Exchange (ETDEWEB)
Zynovchenko, Andriy [Balfour Beatty Rail GmbH, Offenbach (Germany). Abt. Systemtechnik
2011-04-15
Catenary voltage is one of the most important criteria for the design of a railway electrification system. The lowest voltage limits defined by the customer or by EN 50163 and EN 50388 may not be violated. The presented novel technique for improvement of the catenary voltage allows the extension of feeding area of a substation. This makes possible a reduction of the number of substations and enhancement of redundancy grade. (orig.)
Quadratic growth and stability in convex programming problems
Bonnans, J. Frederic; Ioffe, Alexander D.
1994-01-01
Projet PROMATH; Given a convex program with $C^2$ functions and a convex set $S$ of solutions to the problem, we give a second order condition which guarantees that the problem does not have solutions outside of $S$. This condition is interpreted as a characterization for the quadratic growth of the cost function. The crucial role in the proofs is played by a theorem describing a certain uniform regularity property of critical cones in smooth convex programs. We apply these results to the dis...
Restudy of the stability problem of the Schwarzschild black hole
Institute of Scientific and Technical Information of China (English)
Tian Gui-Hua; Wang Shi-Kun; Zhao Zheng
2006-01-01
The stability of the Schwarzschild black hole is restudied in the Painlevé coordinates. Using the Painlevé time coordinate to define the initial time, we reconsider the odd perturbation and find that the Schwarzschild black hole in the Painlevé coordinates is unstable. The Painlevé metric in this paper corresponds to the white-hole-connected region of the Schwarzschild black hole (r ＞ 2m) and the odd perturbation may be regarded as the angular perturbation.Therefore, the white-hole-connected region of the Schwarzschild black hole is unstable with respect to the rotating perturbation.
Rediscussion of the Stability Problem of the Schwarzschild Black Hole
Institute of Scientific and Technical Information of China (English)
Tian Gui-Hua
2006-01-01
@@ We use the Kruskal time coordinate T to define the initial time. By this way, the stability study naturally becomes the one connected with the two regions, i.e. the white-hole-connected region and the black-hole-connected region.The union of the two regions covers the Schwarzschild space-time (r ≥ 2m). We also obtain the very reasonable conclusion: the white-hole-connected region is unstable and the black-hole-connected region is stable.
基于动态响应的电压稳定分析方法%Analysis Method of Voltage Stability based on Dynamic Response
Institute of Scientific and Technical Information of China (English)
王亚俊; 吴佳军; 云雷; 王乙斐; 马志昊; 邵雅宁
2013-01-01
As modern power system is pushed to the maximum operation condition, system voltage stability becomes a significant issue. It is necessary to find out a precise and reliable method to analyze voltage stability. This paper presents a method which is based on the dynamic response theory. This method can analyze stability accurately by calculating Thevenin equivalent parameters and judging the status of voltage stability. The outcomes of IEEE 9-bus power system simulation have confirmed the validity and effectiveness of the method. Under the trend of on-line analysis, this method is of certain significance to on line analysis of voltage stability.%随着电力系统的运行越来越接近其极限状态,电力系统电压稳定问题日益突出,研究一种精确可靠的电压稳定分析方法是非常必要的.提出了一种基于动态响应的电压稳定分析方法,该方法通过计算戴维南等值参数及确定电压稳定判据可以精确实现电压稳定分析.IEEE 9节点算例仿真验证了该方法的正确性和有效性.当在线分析成为趋势的时候,该方法对实现电压稳定的在线分析有一定的现实意义.
Institute of Scientific and Technical Information of China (English)
罗振东; 朱江
2002-01-01
Two simplified and stabilized mixed element formats for the Stokes problem are derived by bubble function, and their convergence,i.e,error analysis, are proved.These formats can save more freedom degrees than other usual formats.
Directory of Open Access Journals (Sweden)
G. Kondrat'ev
1999-10-01
Full Text Available In this article some ideas of Hamilton mechanics and differential-algebraic Geometry are used to exact definition of the potential function (Bellman-Lyapunov function in the optimal stabilization problem of smooth finite-dimensional systems.
Directory of Open Access Journals (Sweden)
G. Kondrat'ev
1999-12-01
Full Text Available In this article some ideas of Hamilton mechanics and differential-algebraic Geometry are used to exact definition of the potential function (Bellman-Lyapunov function in the optimal stabilization problem of smooth finite-dimensional systems.
Some remarks on the stability analysis in Robe's three body problem
Directory of Open Access Journals (Sweden)
R. Meire
1982-01-01
Full Text Available An improved technique is presented for the stability analysis of Robe's 3-body problem which gives more accurate results for the transition curves in the parameter plane than does Robe's paper.
A Note on Existence and Stability of Solutions for Semilinear Dirichlet Problems
Indian Academy of Sciences (India)
Marek Galewski
2011-05-01
We provide existence and stability results for a fourth-order semilinear Dirichlet problem in the case when both the coefficients of the differential operator and the nonlinear term depend on the numerical parameter. We use a dual variational method.
Stability of the inverse resonance problem on the whole line
Bledsoe, Matthew
2012-01-01
In the absence of a half-bound state, a compactly supported potential of a Schr\\"odinger operator on the line is determined up to a translation by the zeros and poles of the meropmorphically continued left (or right) reflection coefficient. The poles are the eigenvalues and resonances, while the zeros also are physically relevant. We prove that all compactly supported potentials (without half-bound states) that have reflection coefficients whose zeros and poles are $\\eps$-close in some disk centered at the origin are also close (in a suitable sense). In addition, we prove stability of small perturbations of the zero potential (which has a half-bound state) from only the eigenvalues and resonances of the perturbation.
Delsart, C; Grimi, N; Boussetta, N; Miot Sertier, C; Ghidossi, R; Vorobiev, E; Mietton Peuchot, M
2016-01-01
In this study, pulsed-electric fields (PEF) and high-voltage electrical discharges (HVED) are proposed as new techniques for the microbial stabilization of red wines before bottling. The efficiency of the treatment was then evaluated. PEF and HVED-treatments have been applied to wine for the inactivation of Oenococcus oeni CRBO 9304, O. oeni CRBO 0608, Pediococcus parvulus CRBO 2.6 and Brettanomyces bruxellensis CB28. Different treatment times (1, 2, 4, 6, 8 and 10 ms) were used at 20 kV cm(-1) for the PEF treatments and at 40 kV for the HVED treatments, which correspond to applied energies from 80 to 800 kJ l(-1) . The effects of the treatments on the microbial inactivation rate and on various characteristics of red wines (phenolic composition, chromatic characteristics and physico-chemical parameters) were measured. The application of PEF or HVED treatments on red wine allowed the inactivation of alteration yeasts (B. bruxellensis CB28) and bacteria (O. oeni CRBO 9304, O. oeni CRBO 0608 and P. parvulus CRBO 2.6). The electric discharges at 40 kV were less effective than the PEF even after 10 ms of treatments. Indeed, 4 ms of PEF treatment at 20 kV cm(-1) were sufficient to inactivate all micro-organisms present in the wines. Also, the use of PEF had no negative impact on the composition of wines compared to the HVED treatments. Contrary to PEF, the phenolics compounds were degraded after the HVED treatment and the physico-chemical composition of wine were modified with HVED. PEF technology seems to be an interesting alternative to stabilize microbiologically wines before bottling and without modifying their composition. This process offers many advantages for winemakers: no chemical inputs, low energy consumption (320 kJ l(-1) ), fast (treatment time of 4 ms) and athermal (ΔT ≈ 10°C). © 2015 The Society for Applied Microbiology.
Stability aspects of the traveling salesman problem based on k-best solutions
Libura, M; van der Poort, ES; Sierksma, C; van der Veen, JAA
1998-01-01
This paper discusses stability analysis for the Traveling Salesman Problem (TSP). For a traveling salesman tour which is known to be optimal with respect to a given instance (length vector) we are interested in determining the stability region, i.e. the set of all length vectors for which the tour
Attention Problems and Stability of WISC-IV Scores Among Clinically Referred Children.
Green Bartoi, Marla; Issner, Jaclyn Beth; Hetterscheidt, Lesley; January, Alicia M; Kuentzel, Jeffrey Garth; Barnett, Douglas
2015-01-01
We examined the stability of Wechsler Intelligence Scale for Children-Fourth Edition (WISC-IV) scores among 51 diverse, clinically referred 8- to 16-year-olds (M(age) = 11.24 years, SD = 2.36). Children were referred to and tested at an urban, university-based training clinic; 70% of eligible children completed follow-up testing 12 months to 40 months later (M = 22.05, SD = 5.94). Stability for index scores ranged from .58 (Processing Speed) to .81 (Verbal Comprehension), with a stability of .86 for Full-Scale IQ. Subtest score stability ranged from .35 (Letter-Number Sequencing) to .81 (Vocabulary). Indexes believed to be more susceptible to concentration (Processing Speed and Working Memory) had lower stability. We also examined attention problems as a potential moderating factor of WISC-IV index and subtest score stability. Children with attention problems had significantly lower stability for Digit Span and Matrix Reasoning subtests compared with children without attention problems. These results provide support for the temporal stability of the WISC-IV and also provide some support for the idea that attention problems contribute to children producing less stable IQ estimates when completing the WISC-IV. We hope our report encourages further examination of this hypothesis and its implications.
STABILIZED FEM FOR CONVECTION-DIFFUSION PROBLEMS ON LAYER-ADAPTED MESHES
Institute of Scientific and Technical Information of China (English)
Hans-G(o)rg Roos
2009-01-01
The application of a standard Galerkin finite element method for convection-diflusion problems leads to oscillations in the discrete solution,therefore stabilization seems to be necessary.We discuss several recent stabilization methods,especially its combination with a Galerkin method on layer-adapted meshes.Supercloseness results obtained allow an improvement of the discrete solution using recovery techniques.
Directory of Open Access Journals (Sweden)
Pengzhan Huang
2011-01-01
Full Text Available Several stabilized finite element methods for the Stokes eigenvalue problem based on the lowest equal-order finite element pair are numerically investigated. They are penalty, regular, multiscale enrichment, and local Gauss integration method. Comparisons between them are carried out, which show that the local Gauss integration method has good stability, efficiency, and accuracy properties, and it is a favorite method among these methods for the Stokes eigenvalue problem.
Institute of Scientific and Technical Information of China (English)
Ehsan Gharib Mombeni; Manoochehr Gharib Mombeini; Lucas Chaves Figueiredo; Debora Testoni Dias
2013-01-01
Objective:To determine the effects of high voltage electrical stimulation (HVES, 800 Voltage) on rapid decreases in pH values and improvements in meat quality. Methods:A total of 50 beef carcasses were applied, divided into two groups, one as a control and another for HVES. Meat quality was evaluated based on M. longissimus dorsi by examining pH and temperature levels at 1, 2, 5, 10 and 24 h, while color stability was examined seven days after slaughter. Results:HVES decreased the pH values of the meat and accelerated rigor mortis (P Conclusion:the HVES had positive effects on meat quality and color stability, in contrast to undesirable consumer preferences.
CSIR Research Space (South Africa)
Botha, PB
2005-10-01
Full Text Available . In recent times, major problems were experienced with chemical stabilization in the Southern African Region, particularly when CEM I 42,5 cement was used. The standard laboratory design procedure worked in the laboratory but did not perform in the field...
The Model and Quadratic Stability Problem of Buck Converter in DCM
Directory of Open Access Journals (Sweden)
Li Xiaojing
2016-01-01
Full Text Available Quadratic stability is an important performance for control systems. At first, the model of Buck Converter in DCM is built based on the theories of hybrid systems and switched linear systems primarily. Then quadratic stability of SLS and hybrid feedback switching rule are introduced. The problem of Buck Converter’s quadratic stability is researched afterwards. In the end, the simulation analysis and verification are provided. Both experimental verification and theoretical analysis results indicate that the output of Buck Converter in DCM has an excellent performance via quadratic stability control and switching rules.
Uniqueness and stability in an inverse problem for a Poisson’s equation
Institute of Scientific and Technical Information of China (English)
2007-01-01
Consider the Poisson’s equation（?）″（x）=-ev-（?）+e（?）-v-N（x）with the Diriehlet boundary data,and we mainly investigate the inverse problem of determining the unknown function N（x）from a parameter function family.Some uniqueness and stability results in the inverse problem are obtained.
Reassessment of problems affecting stabilized layers in roads in South Africa
CSIR Research Space (South Africa)
Paige-Green, P
2009-11-01
Full Text Available any doubt that the problems were related to carbonation of the stabilized materials. A paper was presented at the TREMTI Conference in Paris in 2005 indicating that many of the problems in South Africa that were attributed to carbonation, were actually...
On Existence and Stability of Solutions for Higher Order Semilinear Dirichlet Problems
Indian Academy of Sciences (India)
Marek Galewski
2008-11-01
We provide existence and stability results for semilinear Dirichlet problems with nonlinearity satisfying general growth conditions. We consider the case when both the coefficients of the differential operator and the nonlinear term depend on the numerical parameter. We show applications for the fourth order semilinear Dirichlet problem.
Directory of Open Access Journals (Sweden)
O.V. Golik
2013-09-01
Full Text Available Results of cable transmitting capacity calculation for voltage of up to 220 kV are analyzed. The work is devoted to creation of a current rating calculation technique for high-voltage cross-linked polyethylene cables.
Improving Low Voltage Ride Through Capability of Wind Generators Using Dynamic Voltage Restorer
Sivasankar, Gangatharan; Suresh Kumar, Velu
2014-08-01
The increasing wind power integration with power grid has forced the situation to improve the reliability of wind generators for stable operation. One important problem with induction generator based wind farm is its low ride through capability to the grid voltage disturbance. Any disturbance such as voltage dip may cause wind farm outages. Since wind power contribution is in predominant percentage, such outages may lead to stability problem. The proposed strategy is to use dynamic voltage controller (DVR) to compensate the voltage disturbance. The DVR provides the wind generator the ability to remain connected in grid and improve the reliability. The voltage dips due to symmetrical and unsymmetrical faults are considered for analysis. The vector control scheme is employed for fault compensation which uses software phase locked loop scheme and park dq0 transformation technique. Extensive simulation results are included to illustrate the control and operation of DVR.
On the parabolicity of the Muskat problem: Well-posedness, fingering, and stability results
Escher, Joachim
2010-01-01
We consider in this paper the Muskat problem in a periodic geometry and incorporate capillary as well as gravity effects in the modelling. The problem re-writes as an abstract evolution equation and we use this property to prove well-posedness of the problem and to establish exponential stability of some flat equilibrium. Using bifurcation theory we also find finger shaped steady-states which are all unstable.
Institute of Scientific and Technical Information of China (English)
周毓麟; 沈隆钧; 袁光伟
1996-01-01
The explicit, weak and strong implicit difference solution for the first boundary problem ofquasilinear parabolic system is considered:where u,, and f are m-dimensional vector valued functions, A is an m x m positively definite matrix, andFor this problem, the absolute and relative stability for the general difference schemes is justifiedin the sense of the continuous dependence of the discrete vector solution of the difference schemes on the discrete data of the original problems.
Lipschitz stability in an inverse problem for the Kuramoto-Sivashinsky equation
Baudouin, Lucie; Crépeau, Emmanuelle; Mercado, Alberto
2010-01-01
This paper presents an inverse problem for the Kuramoto-Sivashinsky (K-S) equation. The problem of retrieving the anti-diusion coefficient from a measurement of the solution is discussed. This measurement consists of the solution at some positive time and partial boundary data. Uniqueness and Lipschitz stability for this inverse problem are proven with the Bukhgeim-Klibanov method. The proof is based on a global Carleman inequality for the linearized K-S equation.
移动基站交流稳压技术探讨%Discussion on the AC Voltage Stabilization in the Mobile Stations
Institute of Scientific and Technical Information of China (English)
黄坤材
2001-01-01
Aiming at the national bad status of AC power to the telecom power, the paper dis cusses some issues which should be careful when the mobile base stations select the AC voltage stabilizer, introduces and analysises in detail the performance of various national made stabilizer,such as, mechanic adjustable compensation stabilizer, parameter stabilizer, inductive stabilizer,silicon-control compensation stabilizer. At last, it presents the proposal on the selection of the stabilizer to the mobile base stations.%针对我国通信电源交流供电状况不良的现状，论述了移动通信基站交流稳压器选型应注意的几个问题，详细介绍了国内生产的机械调压补偿式稳压器、参数稳压器、感应式稳压器、可控硅补偿式稳压器等产品性能，并进行了比较。最后提出了移动通信基站交流稳压器选型的建议。
Second-order stabilized explicit Runge-Kutta methods for stiff problems
Martín-Vaquero, J.; Janssen, B.
2009-10-01
Stabilized Runge-Kutta methods (they have also been called Chebyshev-Runge-Kutta methods) are explicit methods with extended stability domains, usually along the negative real axis. They are easy to use (they do not require algebra routines) and are especially suited for MOL discretizations of two- and three-dimensional parabolic partial differential equations. Previous codes based on stabilized Runge-Kutta algorithms were tested with mildly stiff problems. In this paper we show that they have some difficulties to solve efficiently problems where the eigenvalues are very large in absolute value (over 10 5). We also develop a new procedure to build this kind of algorithms and we derive second-order methods with up to 320 stages and good stability properties. These methods are efficient numerical integrators of very large stiff ordinary differential equations. Numerical experiments support the effectiveness of the new algorithms compared to well-known methods as RKC, ROCK2, DUMKA3 and ROCK4.
Optimization of power systems with voltage security constraints
Rosehart, William Daniel
As open access market principles are applied to power systems, significant changes in their operation and control are occurring. In the new marketplace, power systems are operating under higher loading conditions as market influences demand greater attention to operating cost versus stability margins. Since stability continues to be a basic requirement in the operation of any power system, new tools are being considered to analyze the effect of stability on the operating cost of the system, so that system stability can be incorporated into the costs of operating the system. In this thesis, new optimal power flow (OPF) formulations are proposed based on multi-objective methodologies to optimize active and reactive power dispatch while maximizing voltage security in power systems. The effects of minimizing operating costs, minimizing reactive power generation and/or maximizing voltage stability margins are analyzed. Results obtained using the proposed Voltage Stability Constrained OPF formulations are compared and analyzed to suggest possible ways of costing voltage security in power systems. When considering voltage stability margins the importance of system modeling becomes critical, since it has been demonstrated, based on bifurcation analysis, that modeling can have a significant effect of the behavior of power systems, especially at high loading levels. Therefore, this thesis also examines the effects of detailed generator models and several exponential load models. Furthermore, because of its influence on voltage stability, a Static Var Compensator model is also incorporated into the optimization problems.
The return to problem of stability for different-modulus material of beam
Directory of Open Access Journals (Sweden)
L.A. Movsisyan
2007-12-01
Full Text Available The stability of beam made from different-modulus material when two concentrated force act on equal distance from it ends is investigated. Two cases are investigated when forces are directed one to another and vice versa. In dependence from property of material and from points of application of force there are obtained rather different stresses states and therefore different statements of problem of stability.
The motion planning problem and exponential stabilization of a heavy chain. Part II
Directory of Open Access Journals (Sweden)
Piotr Grabowski
2008-01-01
Full Text Available This is the second part of paper [P. Grabowski, The motion planning problem and exponential stabilization of a heavy chain. Part I, to appear in International Journal of Control], where a model of a heavy chain system with a punctual load (tip mass in the form of a system of partial differential equations was interpreted as an abstract semigroup system and then analysed on a Hilbert state space. In particular, in [P. Grabowski, The motion planning problem and exponential stabilization of a heavy chain. Part I, to appear in International Journal of Control] we have formulated the problem of exponential stabilizability of a heavy chain in a given position. It was also shown that the exponential stability can be achieved by applying a stabilizer of the colocated-type. The proof used the method of Lyapunov functionals. In the present paper, we give other two proofs of the exponential stability, which provides an additional intrinsic insight into the exponential stabilizability mechanism. The first proof makes use of some spectral properties of the system. In the second proof, we employ some relationships between exponential stability and exact observability.
2016-01-01
The problem of primary control of high-voltage direct current transmission systems is addressed in this paper, which contains four main contributions. First, to propose a new nonlinear, more realistic, model for the system suitable for primary control design, which takes into account nonlinearities introduced by conventional inner controllers. Second, to determine necessary conditions---dependent on some free controller tuning parameters---for the existence of equilibria. Third, to formulate ...
Thermodynamic stability of charged BTZ black holes: Ensemble dependency problem and its solution
Hendi, S H; Mamasani, R
2015-01-01
Motivated by the wide applications of thermal stability and phase transition, we investigate thermodynamic properties of charged BTZ black holes. We apply the standard method to calculate the heat capacity and the Hessian matrix and find that thermal stability of charged BTZ solutions depends on the choice of ensemble. To overcome this problem, we take into account cosmological constant as a thermodynamical variable. By this modification, we show that the ensemble dependency is eliminated and thermal stability conditions are the same in both ensembles. Then, we generalize our solutions to the case of nonlinear electrodynamics. We show how nonlinear matter field modifies the geometrical behavior of the metric function. We also study phase transition and thermal stability of these black holes in context of both canonical and grand canonical ensembles. We show that by considering the cosmological constant as a thermodynamical variable and modifying the Hessian matrix, the ensemble dependency of thermal stability...
Yakunin, Alexander N.; Aban'shin, Nikolay P.; Akchurin, Garif G.; Akchurin, Georgy G.; Avetisyan, Yuri A.
2016-03-01
The results of the practical implementation of the concept of field-emission current source with high average current density of 0.1-0.3 A-cm-2 are shown. The durability of cathode samples at a level of 6000 hours is achieved under conditions of technical vacuum. A phenomenological model is suggested that describes the tunneling of both equilibrium and nonequilibrium electrons in a vacuum from the zone of concentration of electrostatic field. Conditions are discussed as the resulting increase in the emission current due to the connection mechanism of the photoelectric effect is thermodynamically favorable, that is not accompanied by an undesirable increase in the temperature of the local emission zone. It is shown that to ensure stability and durability of the cathode is also important to limit the concentration of equilibrium carriers using composite structures «DLC film on Mo substrate." This helps to reduce the criticality of the CVC. A possible alternative is to use a restrictive resistance in the cathode. However, this increases the heat losses and thus decreases assembly efficiency. The results of experimental studies of the structure showing the saturation of photoemission current component with an increase in operating voltage. This fact suggests the existence of an effective mechanism for control of emission at constant operating voltage. This is fundamentally important for the stabilization of field emission cathode, providing a reliability and durability. The single-photon processes and the small thickness DLC films (15-20 nm) provide high-speed process of control.
Directory of Open Access Journals (Sweden)
Jilian Wu
2013-01-01
Full Text Available We discuss several stabilized finite element methods, which are penalty, regular, multiscale enrichment, and local Gauss integration method, for the steady incompressible flow problem with damping based on the lowest equal-order finite element space pair. Then we give the numerical comparisons between them in three numerical examples which show that the local Gauss integration method has good stability, efficiency, and accuracy properties and it is better than the others for the steady incompressible flow problem with damping on the whole. However, to our surprise, the regular method spends less CPU-time and has better accuracy properties by using Crout solver.
Heister, Timo
2012-01-29
Efficient preconditioning for Oseen-type problems is an active research topic. We present a novel approach leveraging stabilization for inf-sup stable discretizations. The Grad-Div stabilization shares the algebraic properties with an augmented Lagrangian-type term. Both simplify the approximation of the Schur complement, especially in the convection-dominated case. We exploit this for the construction of the preconditioner. Solving the discretized Oseen problem with an iterative Krylov-type method shows that the outer iteration numbers are retained independent of mesh size, viscosity, and finite element order. Thus, the preconditioner is very competitive. © 2012 John Wiley & Sons, Ltd.
DEFF Research Database (Denmark)
Liu, Hongzhi; Chen, Zhe; Liu, Leo
2013-01-01
. In this paper, VSC-HVDC transmission system is used to integrate a large-scale wind power plant into the onshore power grid. For different voltage support strategies of VSC-HVDC, a trajectory sensitivity analysisbased approach is proposed to find the minimum onshore VSC capacity with which the VSC-HVDC can...
High voltage stability of LiCoO2 particles with a nano-scale Lipon coating
Energy Technology Data Exchange (ETDEWEB)
Kim, Yoongu [ORNL; Veith, Gabriel M [ORNL; Nanda, Jagjit [ORNL; Unocic, Raymond R [ORNL; Dudney, Nancy J [ORNL
2011-01-01
For high-voltage cycling of rechargeable Li batteries, a nano-scale amorphous Li-ion conductor, lithium phosphorus oxynitride (Lipon), has been coated on surfaces of LiCoO{sub 2} particles by combining a RF-magnetron sputtering technique and mechanical agitation of LiCoO{sub 2} powders. LiCoO{sub 2} particles coated with 0.36 wt% ({approx}1 nm thick) of the amorphous Lipon, retain 90% of their original capacity compared to non-coated cathode materials that retain only 65% of their original capacity after more than 40 cycles in the 3.0-4.4 V range with a standard carbonate electrolyte. The reason for the better high-voltage cycling behavior is attributed to reduction in the side reactions that cause increase of the cell resistance during cycling. Further, Lipon coated particles are not damaged, whereas uncoated particles are badly cracked after cycling. Extending the charge of Lipon-coated LiCoO{sub 2} to higher voltage enhances the specific capacity, but more importantly the Lipon-coated material is also more stable and tolerant of high voltage excursions. A drawback of Lipon coating, particularly as thicker films are applied to cathode powders, is the increased electronic resistance that reduces the power performance.
Improved Passive-Damped LCL Filter to Enhance Stability in Grid-Connected Voltage-Source Converters
DEFF Research Database (Denmark)
Beres, Remus Narcis; Wang, Xiongfei; Blaabjerg, Frede;
2015-01-01
This paper proposes an improved passive-damped LCL filter to be used as interface between the grid-connected voltage-source converters and the utility grid. The proposed filter replaces the LCL filter capacitor with a traditional C-type filter with the resonant circuit tuned in such a way that sw...
SHAPE STABILITY OF OPTIMAL CONTROL PROBLEMS IN COEFFICIENTS FOR COUPLED SYSTEM OF HAMMERSTEIN TYPE
Directory of Open Access Journals (Sweden)
P. I. Kogut
2014-01-01
Full Text Available In this paper we consider an optimal control problem (OCP for the coupledsystem of a nonlinear monotone Dirichlet problem with matrix-valued L∞(Ω;RN×N-controls in coecients and a nonlinear equation of Hammerstein type, where solution nonlinearly depends on L∞ -control. Since problems of this type have no solutions in general, we make a special assumption on the coecients of the state equations and introduce the class of so-called solenoidal admissible controls. Using the direct method in calculus of variations, we prove the existence of an optimal control. We also study the stability of the optimal control problem with respect to the domain perturbation. In particular, we derive the sucient conditions of the Mosco-stability for the given class of OCPs.
ASYMPTOTIC BEHAVIOUR AND EXPONENTIAL STABILITY FOR THERMOELASTIC PROBLEM WITH LOCALIZED DAMPING
Institute of Scientific and Technical Information of China (English)
GAO Hong-jun; ZHAO Yu-juan
2006-01-01
A semi-linear thermoelastic problem with localized damping is considered,which is one of the most important mathematical models in material science. The existence and decays exponentially to zero of solution of this problem are obtained. Moreover,the existence of absorbing sets is achieved in the non-homogeneous case. The result indicates that the system which we studied here is asymptotic stability.
Uniqueness and local stability for the inverse scattering problem of determining the cavity
Institute of Scientific and Technical Information of China (English)
FENG; Lixin; MA; Fuming
2005-01-01
Considering a time-harmonic electromagnetic plane wave incident on an arbitrarily shaped open cavity embedded in infinite ground plane, the physical process is modelled by Maxwell's equations. We investigate the inverse problem of determining the shape of the open cavity from the information of the measured scattered field. Results on the uniqueness and the local stability of the inverse problem in the 2-dimensional TM (transverse magnetic) polarization are proved in this paper.
Real-time Monitoring System of Voltage Stability Based on Web%基于Web的电压稳定实时监控系统
Institute of Scientific and Technical Information of China (English)
张小兵; 李连伟; 郭湘勇
2011-01-01
为了满足电网调度人员实时了解电网电压运行情况的需要,开发了基于Web的电力系统电压稳定在线监控系统,该系统后台使用C++,Java等语言开发,前台使用extjs等脚本技术,数据库采用SQL server 2000.数据源来自EMS(能量管理系统)文本.开发过程使用MyEclipse 7.1工具.系统能够根据用户需求发布基态情况下和故障(N-1)情况下负荷裕度、区域裕度、裕度灵敏度等电压稳定分析数据,自定义参数进行预防控制.开发实例证明,采用Java,extjs技术开发可以提高系统开发效率,采用B/S模式加强系统的通用性,较好地满足电力系统电压稳定在线监控和分析的需求.%In order to meet the needs of dispatching and monitoring the voltage stability of power grid in real-time, a monitoring system of voltage stability is designed based on Web. The programming of web in the server system is exploited by C++, Java and so on, while the interface is exploited by the script technique, and the database management system is exploited by SQL server 2000. The data source comes from the EMS(electic management system) text. During the development process using the tools of Myeclipse, according to the need of users, the developmented system can release the voltage stability data in the state of normal or N-1 like the load margin, area margin, the sensitivity of load margin and so on. The example shows that the system designed with the technique of Java and Extjs can improve development efficiency, better the program universality and satisfy the demands of real-time monitoring and analyse voltage stability.
Relationship problems over the early years of marriage: stability or change?
Lavner, Justin A; Karney, Benjamin R; Bradbury, Thomas N
2014-12-01
Although couples' management of differences and problems is widely assumed to be central to the course and outcome of their relationships, some theoretical perspectives hold that marital conflicts increase over the newlywed years, whereas others maintain that couples' problems remain stable. We tested these opposing views by examining changes in marital problems and marital satisfaction over the first 4 years of marriage in a sample of 169 newlywed couples. Although marital satisfaction declined on average, overall levels of marital problems remained stable. Analyses of 19 specific problems generally revealed considerable stability as well, although husbands and wives rated showing affection as increasingly problematic over time. These findings challenge longstanding assumptions regarding the role of accumulating conflict in marital functioning over time and suggest that specific and overall problems in marriage largely remain stable over the newlywed years. Implications for theory and clinical practice are discussed.
Long term stability of power systems
Energy Technology Data Exchange (ETDEWEB)
Kundur, P.; Gao, B. [Powertech Labs. Inc., Surrey, BC (Canada)
1994-12-31
Power system long term stability is still a developing subject. In this paper we provide our perspectives and experiences related to long term stability. The paper begins with the description of the nature of the long term stability problem, followed by the discussion of issues related to the modeling and solution techniques of tools for long term stability analysis. Cases studies are presented to illustrate the voltage stability aspect and plant dynamics aspect of long term stability. (author) 20 refs., 11 figs.
A Chebyshev collocation method for solving two-phase flow stability problems
Boomkamp, P.A.M.; Boersma, B.J.; Miesen, R.H.M.; Beijnon, G.V.
1997-01-01
This paper describes a Chebyshev collocation method for solving the eigenvalue problem that governs the stability of parallel two-phase flow. The method is based on the expansion of the eigenfunctions in terms of Chebyshev polynomials, point collocation, and the subsequent solution of the resulting
Abouelmagd, Elbaz I.
2012-11-01
In this paper, we prove that the locations of the triangular points and their linear stability are affected by the oblateness of the more massive primary in the planar circular restricted three-body problem, considering the effect of oblateness for J 2 and J 4. After that, we show that the triangular points are stable for 0Caliban systems.
Kan, K.J.; Dolan, C.V.; Nivard, M.G.; Middeldorp, C.M.; van Beijsterveldt, C.E.M.; Willemsen, G.; Boomsma, D.I.
2013-01-01
Objective: To review findings on attention-deficit/hyperactivity disorder and attention problems (AP) in children, adolescents, and adults, as established in the database of the Netherlands Twin Register and increase the understanding of stability in AP across the lifespan as a function of genetic a
Dutt, Pravir; Tomar, Satyendra
2003-01-01
In this paper we show that the h-p spectral element method developed in [3,8,9] applies to elliptic problems in curvilinear polygons with mixed Neumann and Dirichlet boundary conditions provided that the Babuska-Brezzi inf-sup conditions are satisfied. We establish basic stability estimates for a no
Kan, Kees-Jan; Dolan, Conor V.; Nivard, Michel G.; Middeldorp, Christel M.; van Beijsterveldt, Catharina E. M.; Willemsen, Gonneke; Boomsma, Dorret I.
2013-01-01
Objective: To review findings on attention-deficit/hyperactivity disorder and attention problems (AP) in children, adolescents, and adults, as established in the database of the Netherlands Twin Register and increase the understanding of stability in AP across the lifespan as a function of genetic and environmental influences. Method: A…
Transfers and Exchange-Stability in Two-Sided Matching Problems
Lazarova, E.A.; Borm, P.E.M.; Estevez, A.
2014-01-01
In this paper we consider one-to-many matching problems where the preferences of the agents involved are represented by monetary reward functions. We characterize Pareto optimal matchings by means of contractually exchange stability and matchings of maximum total reward by means of compensation exch
The existence and the stability of solutions for equilibrium problems with lower and upper bounds
Directory of Open Access Journals (Sweden)
Congjun Zhang
2012-12-01
Full Text Available In this paper, we study a class of equilibrium problems with lower and upper bounds. We obtain some existence results of solutions for equilibrium problems with lower and upper bounds by employing some classical fixed-point theorems. We investigate the stability of the solution sets for the problems, and establish sufficient conditions for the upper semicontinuity, lower semicontinuity and continuity of the solution set mapping $S:Lambda_1imesLambda_2o2^{X}$ in a Hausdorff topological vector space, in the case where a set $K$ and a mapping $f$ are perturbed respectively by parameters $lambda$ and $mu.$
基于同步相量测量的电压稳定指标%Voltage stability index based on synchronized phasor measurement
Institute of Scientific and Technical Information of China (English)
随慧斌; 赵建国
2008-01-01
A voltage stability index based on synchronized phasor measurements is presented for transmission systems.Power system can be decoupled into several power transmission paths.The ratio of the voltage-drop projection on the start node voltage in a transmission path to the start node voltage is taken as the voltage stability index of power system.which is calculated directly with the loeal vohage phasor information and the weakest transmission path.the complex power flow calculation being thus avoided.Based on a fast and effective PMU(Phasor Measurement Unit)placement.phasor information is provided by direct measurement or indirect calculation of PMUs.The weakest transmission path is determined by the graph theory.By calculating the index value of the weakest transmission path,which approaches to 0.5 when system is prone to voltage collapse,and considering the power system reactive power reserve,the voltage stability can be assessed.Simulation results of IEEE 5-bus and IEEE 30-bus networks show its validity in system collapse prediction.%针对输电网提出了一种基于同步相量测量信息的电压稳定指标.电力系统可以分解成许多电能传输路径.以传输路径首节点电压与末节点电压在首节点电压上的投影之差与首节点电压的比值作为计算电压稳定与否的指标.该指标根据最弱电能传输路径利用局部电压相量测量信息直接计算得出,避免了复杂的潮流计算.局部电压相量测量数据由相量测量单元PMU提供.基于一种快速有效的PMU配置方法.利用直接测量或间接计算的数据作为此稳定指标计算所需要的电压相量信息.运用图论的基本思想寻找电能最弱传输路径.通过计算电能最弱传输路径的电压稳定指标和系统无功储备情况判断系统电压稳定度,当系统接近不稳定状态时,最弱传输路径的电压稳定指标值趋向于临界值0.5.在IEEE 5节点和IEEE 30节点系统上的仿真表明了该指
计及风力发电的配电网电压稳定性评估框架研究%Voltage stability assessment frame for distribution network with wind farms
Institute of Scientific and Technical Information of China (English)
刘新东; 郭容; 张建芬; 曾锐明
2013-01-01
A method of distribution network voltage stability assessment with power circle index is presented. By means of calculating the index of voltage stability, security of power grid structures and reliability of power consumption, the composite indicator of the distribution network is introduced. The voltage stability is assessed in three steps:when wind farm is integrated into the network, the impulse current flowing through the power circle is calculated and voltage sag of load point is obtained to assess voltage stability; when it exits from the network, voltage stability is assessed by calculating voltage drop with the loss of voltage support;when it generates fluctuant power continually, the change of power flow in the network is considered and voltage stability assessment equation is reconstructed to determine voltage stability with active and reactive power of wind farm. Taking the IEEE123 as the sample, the effectiveness of the voltage stability assessment frame for distribution network with wind farms is proved. This work is supported by National Natural Science Foundation of China (No. 51007030).%把风电场功率圆的稳定性作为评估配电网稳定性的依据之一，计算功率圆的电压稳定性、电网架构安全性和用户用电的可靠性等指标，最后提出配电网的安全性综合指标。分三种情况对电压稳定性进行评估：风电场并入网络时，计算流进负荷点的冲击电流，得到电压波动情况，评估网络电压稳定性；风电场切出网络时，计算负荷点失去电压支撑的大小得到电压跌落情况，评估网络电压稳定性；风电场间歇输出功率时，考虑风电场改变配电网的功率潮流，重新构造电网电压稳定指标，根据风电场的有功和无功判断系统电压稳定性。最后以IEEE123节点系统为例，验证了所提计及风力发电的配电网电压稳定评估框架的有效性。
Do, H. Q.; Massa, F.; Tison, T.; Lallemand, B.
2017-02-01
This paper presents a numerical strategy to reanalyze the modified frequency stability analysis of friction induced vibration problem. The stability analysis of a mechanical system relies on several coupling steps, namely a non-linear static analysis followed by linear and complex eigenvalue problems. We thus propose a numerical strategy to perform more rapidly multiple complex eigenvalue analyses. This strategy couples three methods namely, Fuzzy Logic Controllers to manage frictional contact problem, homotopy developments and projection techniques to reanalyze the projection matrices and component mode synthesis to calculate the modified eigensolutions. A numerical application is performed to highlight the efficiency of the strategy and a discussion is proposed in terms of precision and computational time.
Partial Stability Approach to Consensus Problem of Linear Multi-agent Systems
Institute of Scientific and Technical Information of China (English)
CHEN Yang-Zhou; GE Yan-Rong; ZHANG Ya-Xiao
2014-01-01
A linear transformation is proposed to deal with the consensus problem of high-order linear multi-agent systems (LMASs). In virtue of the linear transformation, the consensus problem is equivalently translated into a partial stability problem. We discuss three issues of the LMASs under a generalized linear protocol: 1) to find criteria of consensus convergence;2) to calculate consensus function; 3) to design gain matrices in the linear consensus protocol. Precisely, we provide a necessary and suﬃcient criterion of consensus convergence in terms of Hurwitz stability of a matrix and give an analytical expression of the consensus function. In addition, we set up a relation between the gain matrices in the protocol and the convergence time and consensus accuracy of the agents, and then design the gain matrices with respect to a pre-specified convergence time and a required consensus accuracy.
Directory of Open Access Journals (Sweden)
D. A. Eliseev
2015-01-01
Full Text Available The solution stability of an initial boundary problem for a linear hybrid system of differential equations, which models the rotation of a rigid body with two elastic rods located in the same plane is studied in the paper. To an axis passing through the mass center of the rigid body perpendicularly to the rods location plane is applied the stabilizing moment proportional to the angle of the system rotation, derivative of the angle, integral of the angle. The external moment provides a feedback. A method of studying the behavior of solutions of the initial boundary problem is proposed. This method allows to exclude from the hybrid system of differential equations partial differential equations, which describe the dynamics of distributed elements of a mechanical system. It allows us to build one equation for an angle of the system rotation. Its characteristic equation defines the stability of solutions of all the system. In the space of feedback-coefficients the areas that provide the asymptotic stability of solutions of the initial boundary problem are built up.
Institute of Scientific and Technical Information of China (English)
付小伟; 王进; 郭伟; 郑剑武
2012-01-01
Uncertainty of wind power resources and operating characteristics of the wind turbine itself makes wind turbine output power of change, which is equivalent to big power system disturbances. With the gradual increase of wind power penetration, it＇s high time to study the Voltage stability of large grid-connected wind power operation problem, it detail analyses the effect of voltage stability about wind farm under different wind speed model, installed capacity of wind power and fault clearing time. The static synchronous compensator applied to wind farms, according to the simulation results, the voltage restore rapidly after the faults cleared, so the low voltage ride through（LVRT）capability of wind turbines is improved, ensures the continuous operation of wind turbines and the security of the power network%风力资源的不确定性和风电机组本身的运行特性使风电机组的输出功率随之变化，对电力系统来说相当于一个大的扰动。随着风电穿透功率的逐步增加，大规模风电并网运行的电压稳定性问题亟待研究。利用Matlab／Simulink建立风电场仿真模型，详细分析了不同风速模型、风电场装机容量及短路故障切除时间下风电场对电压稳定性的影响。把静止同步补偿器（StaticSynchronousCompensator，STATCOM）应用到风电场中，仿真结果表明，STATCOM可以改善风电场的电压稳定性，提高了风电机组的低电压穿越能力，确保风电机组连续运行及电网安全稳定。
Institute of Scientific and Technical Information of China (English)
邵庆华; 邵昱; 赵波; 时永胜; 罗禹
2013-01-01
The voltage stability of a real power system connected with a wind farm is simulated. The impact of voltage stability of wind farm connected system is studied through the simulation and calculation of real network. The degree of system transient stability is compared through wind disturbance and impedance variation of wind farm connected system, and draw the conclusion of voltage stability after the connection of wind farm.%对风电场接入地区电网后的电压稳定性进行了仿真研究.对实际电网进行仿真计算,通过风速扰动及改变风电场接入系统的阻抗值,比较系统电压暂态稳定性的程度,并得出地区电网在风电接入后的电压稳定性结论.
Stability of Complex-Rotation Method on a Simple Resonant Scattering Problem
Institute of Scientific and Technical Information of China (English)
SHEN Li; WANG Lei; LIU Xiao-Jun; SHI Ting-Yun; LIU Hong-Ping
2008-01-01
@@ The stability of the complex-rotation method in B-spline basis for a simple atomic resonant scattering problem in free field is investigated. The numerical calculation shows that this method has a feature that the solution will not change in a wide range of rotation angle θ. Our determined scattering resonant energies and widths exactly coincide with the popularly accepted values. A new resonance is identified numerically although it is very broad.The norm of the complex eigenvalue, [E], is proposed to investigate and to evaluate the stability of the obtained complex eigenvalues.
Energy Technology Data Exchange (ETDEWEB)
Bornard, P. [Reseau de Transport d' Electricite (RTE), Div. Systeme Electrique, 92 - Paris la Defense (France); Pavard, M. [Electricite de France (EDF), 75 - Paris (France); Testud, G. [Reseau de Transport d' Electricite (RTE), Dept. Exploitation du Systeme Electrique, 92 - Paris la Defense (France)
2005-10-01
Keeping the mastery of the safety of a power transportation system and respecting the contractual commitments with respect to the network users implies the implementation of efficient frequency and voltage adjustment systems. This article presents a synthetic overview of the methods and means implemented to ensure the adjustment of the voltage and frequency and the stability of very-high voltage power transportation networks: 1 - recalls of the general problem; 2 - frequency and active power adjustment: adapting generation to consumption, adapting consumption to generation; 3 - voltage and reactive power adjustment: duality of the voltage-reactive compensation adjustment, compensation of the reactive power, voltage adjustment chain, voltage adjustment of very high voltage networks, collapse of the voltage plan; 4 - alternators stability: static stability, transient stability, numerical simulation methods, stability improvement; 5 - conclusion. (J.S.)
Boundary Value Problem for Analysis of Portal Double-Row Stabilizing Piles
Directory of Open Access Journals (Sweden)
Cheng Huang
2013-01-01
Full Text Available This paper presents a new numerical approach for computing the internal force and displacement of portal double-row piles used to stabilize potential landslide. First, the new differential equations governing the mechanical behaviour of the stabilizing pile are formulated and the boundary conditions are mathematically specified. Then, the problem is numerically solved by the high-accuracy Runge-Kutta finite difference method. A program package has been developed in MATLAB depending on the proposed algorithm. Illustrative examples are presented to demonstrate the validity of the developed program. In short, the proposed approach is a practical new idea for analyzing the portal double-row stabilizing pile as a useful supplement to traditional methods such as FEM.
On the Physical Problem of Spatial Dimensions: An Alternative Procedure to Stability Arguments
Caruso, Francisco
2012-01-01
Why is space 3-dimensional? The first answer to this question, entirely based on Physics, was given by Ehrenfest, in 1917, who showed that the stability requirement for $n$-dimensional two-body planetary system very strongly constrains space dimensionality, favoring 3-d. This kind of approach will be generically called "stability postulate" throughout this paper and was shown by Tangherlini, in 1963, to be still valid in the framework of general relativity as well as for quantum mechanical hydrogen atom, giving the same constraint for space-dimensionality. In the present work, before criticizing this methodology, a brief discussion has been introduced, aimed at stressing and clarifying some general physical aspects of the problem of how to determine the number of space dimensions. Then, the epistemological consequences of Ehrenfest's methodology are critically reviewed. An alternative procedure to get at the proper number of dimensions, in which the stability postulate (and the implicit singularities in three...
The moduli and gravitino (non)-problems in models with strongly stabilized moduli
Energy Technology Data Exchange (ETDEWEB)
Evans, Jason L.; Olive, Keith A. [William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN, 55455 (United States); Garcia, Marcos A.G., E-mail: jlevans@umn.edu, E-mail: garciagarcia@physics.umn.edu, E-mail: olive@physics.umn.edu [School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN, 55455 (United States)
2014-03-01
In gravity mediated models and in particular in models with strongly stabilized moduli, there is a natural hierarchy between gaugino masses, the gravitino mass and moduli masses: m{sub 1/2} << m{sub 3/2} << m{sub φ}. Given this hierarchy, we show that 1) moduli problems associated with excess entropy production from moduli decay and 2) problems associated with moduli/gravitino decays to neutralinos are non-existent. Placed in an inflationary context, we show that the amplitude of moduli oscillations are severely limited by strong stabilization. Moduli oscillations may then never come to dominate the energy density of the Universe. As a consequence, moduli decay to gravitinos and their subsequent decay to neutralinos need not overpopulate the cold dark matter density.
The Moduli and Gravitino (non)-Problems in Models with Strongly Stabilized Moduli
Evans, Jason L; Olive, Keith A
2013-01-01
In gravity mediated models and in particular in models with strongly stabilized moduli, there is a natural hierarchy between gaugino masses, the gravitino mass and moduli masses: $m_{1/2} \\ll m_{3/2} \\ll m_{\\phi}$. Given this hierarchy, we show that 1) moduli problems associated with excess entropy production from moduli decay and 2) problems associated with moduli/gravitino decays to neutralinos are non-existent. Placed in an inflationary context, we show that the amplitude of moduli oscillations are severely limited by strong stabilization. Moduli oscillations may then never come to dominate the energy density of the Universe. As a consequence, moduli decay to gravitinos and their subsequent decay to neutralinos need not overpopulate the cold dark matter density.
The Stability of the Constrained Utility Maximization Problem - A BSDE Approach
Mocha, Markus
2011-01-01
This article studies the sensitivity of the power utility maximization problem with respect to the investor's relative risk aversion, the statistical probability measure, the investment constraints and the market price of risk. We extend previous descriptions of the dual domain then exploit the link between the constrained utility maximization problem and continuous semimartingale quadratic BSDEs to reduce questions on sensitivity to results on stability for such equations. This then allows us to prove appropriate convergence of the primal and dual optimizers in the semimartingale topology.
Stability of stationary solutions for inflow problem on the micropolar fluid model
Yin, Haiyan
2017-04-01
In this paper, we study the asymptotic behavior of solutions to the initial boundary value problem for the micropolar fluid model in a half-line R+:=(0,∞). We prove that the corresponding stationary solutions of the small amplitude to the inflow problem for the micropolar fluid model are time asymptotically stable under small H1 perturbations in both the subsonic and degenerate cases. The microrotation velocity brings us some additional troubles compared with Navier-Stokes equations in the absence of the microrotation velocity. The proof of asymptotic stability is based on the basic energy method.
Wang, Qi; Hou, Yubin; Wang, Junting; Lu, Qingyou
2013-11-01
We present a novel homebuilt scanning tunneling microscope (STM) with high quality atomic resolution. It is equipped with a small but powerful GeckoDrive piezoelectric motor which drives a miniature and detachable scanning part to implement coarse approach. The scanning part is a tiny piezoelectric tube scanner (industry type: PZT-8, whose d31 coefficient is one of the lowest) housed in a slightly bigger polished sapphire tube, which is riding on and spring clamped against the knife edges of a tungsten slot. The STM so constructed shows low back-lashing and drifting and high repeatability and immunity to external vibrations. These are confirmed by its low imaging voltages, low distortions in the spiral scanned images, and high atomic resolution quality even when the STM is placed on the ground of the fifth floor without any external or internal vibration isolation devices.
Nakamura, M.; Meier, D. L.
2009-08-01
What can we expect in the VSOP-2 mission to reveal the sub parsec scale structures of AGN jets? Based on the MHD process of jet formation and evolution, we discuss about unsolved problems of sub parsec AGN jets in terms of the acceleration, the collimation, and the stability properties. Several key features will be proved by the VSOP-2 observations; they play an important role in determining how the MHD process will work in the jet dynamics.
Marras, Simone
2012-01-01
Premi extraordinari doctorat curs 2012-2013, àmbit d’Enginyeria Civil In this thesis the finite and spectral element methods (FEM and SEM, respectively) applied to problems in atmospheric simulations are explored through the common thread of Variational Multiscale Stabilization (VMS). This effort is justified by three main reasons. (i) the recognized need for new solvers that can efficiently execute on massively parallel architectures ¿a spreading framework in most fields of co...
Slowik, Daria; Henderson, Richard
2015-01-01
With the ultimate goal of detailed structural analysis of mammalian and particularly human voltage-gated sodium channels (VGSCs), we have investigated the relative stability of human and rat VGSCs and compared them with electric eel VGSC. We found that NaV1.3 from rat was the most stable after detergent solubilisation. The order of stability was rNaV1.3 > hNaV1.2 > hNaV1.1 > hNaV1.6 > hNaV1.3 > hNaV1.4. However, a comparison with the VGSC from Electrophorus electricus, which is most similar to NaV1.4, shows that the eel VGSC is considerably more stable in detergent than the human VGSCs examined. We conclude that current methods of structural analysis, such as single particle electron cryomicroscopy (cryoEM), may be most usefully targeted to eel VGSC or rNaV1.3, but that structural analysis on the full spectrum of VGSCs, by methods that require greater stability such as crystallisation and X-ray crystallography, will require further stabilisation of the channel. PMID:25838126
Slowik, Daria; Henderson, Richard
2015-07-01
With the ultimate goal of detailed structural analysis of mammalian and particularly human voltage-gated sodium channels (VGSCs), we have investigated the relative stability of human and rat VGSCs and compared them with electric eel VGSC. We found that NaV1.3 from rat was the most stable after detergent solubilisation. The order of stability was rNaV1.3>hNaV1.2>hNaV1.1>hNaV1.6>hNaV1.3>hNaV1.4. However, a comparison with the VGSC from Electrophorus electricus, which is most similar to NaV1.4, shows that the eel VGSC is considerably more stable in detergent than the human VGSCs examined. We conclude that current methods of structural analysis, such as single particle electron cryomicroscopy (cryoEM), may be most usefully targeted to eel VGSC or rNaV1.3, but that structural analysis on the full spectrum of VGSCs, by methods that require greater stability such as crystallisation and X-ray crystallography, will require further stabilisation of the channel.
DEFF Research Database (Denmark)
Bieniasz, Leslaw K.; Østerby, Ole; Britz, Dieter
1995-01-01
The stepwise numerical stability of the Saul'yev finite difference discretization of an example diffusional initial boundary value problem from electrochemical kinetics has been investigated using the matrix method of stability analysis. Special attention has been paid to the effect...
基于广域测量系统的电压稳定指标%A On-Line Voltage Stability Index Based on Wide Area Measurement System
Institute of Scientific and Technical Information of China (English)
巩伟峥; 房鑫炎
2011-01-01
综述和比较了多种基于广域测量的在线电压静态稳定指标,通过理论分析指出了这几种指标的理论缺陷和使用限制.利用同步测量的母线电压相量、线路潮流等电气量,根据线路潮流电压方程计算比较线路两侧电压水平,提出了一种新的电压稳定性指标Ivs,指示被监测线路或母线的电压稳定情况.通过系统等效的方法解耦多机系统的线路电压耦合性,可将该指标推广到多机系统.在单机单负荷系统和IEEE 14节点系统的仿真表明,Ivs可以准确快速地判断系统线路电压稳定情况,预测线路电压失稳点,且适用于所有种类的线路.与之前的电压静态稳定指标相比,Ivs具有无需判断线路电阻,物理概念清晰,适用范围广,线性度好等优点,有利于实现在线电压稳定监测和评估.%On-line steady state voltage stability indices based on wide area measurement system (WAMS) are summarized and compared. Based on theoretical analysis, the theoretical defects and usage limitations of these indices are pointed out. Utilizing synchronously measured electric quantities such as bus voltage phasors and line power flows and according to the comparison results of voltage levels, which are calculated by power flow and voltage equations of transmission line, at both terminals oftransmission lines, a new voltage stability index Ivs is proposed to indicate the voltage stability condition of monitored bus or transmission line. By means of system equivalence, the coupling of line voltage in multi-machine power system is decoupled, thus the proposed voltage stability index can be applied to multi-machine power system. Simulation results fiom single-machine single-load system and IEEE 14-bus system show that voltage stability condition of transmission line can be rapidly judged and the voltage instability point can be predicted by the proposed index IVS, and the proposed index is suitable to all kinds of transmission
Institute of Scientific and Technical Information of China (English)
董雷; 张昭; 蒲天骄; 于汀; 韩巍
2015-01-01
为实现对电压稳定的实时在线监测，亟需研究具有良好精确度、线性度和计算快速性的电压稳定在线评估指标，为此提出一种新的基于支路电压方程可行解域的静态电压稳定Lu指标。该指标可由PMU的局部量测信息快速计算获得。进而，为了消除冗余量测信息对指标精确度的影响，提出了仅利用PMU电压量测信息的Lu改进指标Lu.pro。最后，通过仿真算例验证了Lu及Lu.pro指标具有很好的准确性和线性度，并进一步验证了Lu.pro指标在三相不对称情况下的适用性和有效性。结果表明，Lu指标以及改进的Lu.pro指标能够反映系统中电压稳定的薄弱节点及区域，适用于电压稳定的在线监测与评估。%To realize online monitoring of system voltage stability, it is in urgent need of proposing a voltage stability index with ideal accuracy, linearity and computation speed. This paper proposes a new voltage stability index ofLu based on the feasible solution domain of branch voltage equation which can be fast calculated using the local measurement information of PMU. Moreover, in order to eliminate the error produced by redundant measurement information, the improved indexLu.pro is proposed which can be calculated merely with the voltage measurement information of PMU. Simulations are made to prove thatLu andLu.pro are ideal voltage stability indexes with good accuracy and linearity. Furthermore, it is also demonstrated by simulations thatLu.procan be used to evaluate the voltage stability of three-phase unbalanced system. Simulation results show that indexes ofLu andLu.pro can indicate the weak nodes and areas of voltage stability which can be used in online monitoring and evaluation of voltage stability.
Lagrangian relative equilibria for a gyrostat in the three-body problem: bifurcations and stability
Energy Technology Data Exchange (ETDEWEB)
Guirao, Juan L G; Vera, Juan A, E-mail: juan.garcia@upct.e, E-mail: juanantonio.vera@upct.e [Departamento de Matematica Aplicada y EstadIstica, Universidad Politecnica de Cartagena, Hospital de Marina, 30203 Cartagena, Region de Murcia (Spain)
2010-05-14
In this paper we consider the non-canonical Hamiltonian dynamics of a gyrostat in the frame of the three-body problem. Using geometric/mechanic methods we study the approximate dynamics of the truncated Legendre series representation of the potential of an arbitrary order. Working in the reduced problem, we study the existence of relative equilibria that we refer to as Lagrange type following the analogy with the standard techniques. We provide necessary and sufficient conditions for the linear stability of Lagrangian relative equilibria if the gyrostat morphology form is close to a sphere. Thus, we generalize the classical results on equilibria of the three-body problem and many results on them obtained by the classic approach for the case of rigid bodies.
Indian Academy of Sciences (India)
V Ganesh; M Subbiah
2013-05-01
We generalize Tollmien’s solutions of the Rayleigh problem of hydrodynamic stability to the case of arbitrary channel cross sections, known as the extended Rayleigh problem. We prove the existence of a neutrally stable eigensolution with wave number $k_s>0$; it is also shown that instability is possible only for $0 < k < k_s$ and not for $k>k_s$. Then we generalize the Tollmien–Lin perturbation formula for the behavior of $c_i$, the imaginary part of the phase velocity as the wave number $k→ k_s$ − to the extended Rayleigh problem and subsequently, we use this formula to demonstrate the instability of a particular shear flow.
Institute of Scientific and Technical Information of China (English)
林舜江; 刘明波
2011-01-01
构建了负荷采用三阶感应电动机并联恒阻抗表示的电力系统短期电压稳定分析数学模型,并推导出负荷增减的表示方法.根据系统小干扰方程状态矩阵特征值为零的特点,提出了计算小干扰电压稳定极限点的数学模型,以求得N-1故障后系统从当前运行状态到电压稳定极限点需增减的负荷.通过对发电机稳态方程中功角的三角函数项引入辅助变量,将极限点计算模型转化为关于未知量的线性或二次函数,进而可采用最优乘子牛顿法计算极限点,以解决极限点处系统稳态方程雅可比矩阵奇异带来的收敛困难.IEEE9节点系统和IEEE39节点系统的计算结果表明该方法能够可靠地收敛到N-1故障后系统的小干扰电压稳定极限点.%The three-order induction motor paralleled with constant impedance model is used to represent the load, and the mathematical model of analyzing the short-term voltage stability of power system is established. The representation of load increasing and shedding is also deduced. Based on the characteristic that the state matrix of small disturbance equations has zero eigenvalue, the mathematical model of computing the small disturbance voltage stability limit point is proposed, and the load need to be increased or be sheded from current state to voltage stability limit point of the system under N-I contingencies can be computed.By introducing auxiliary variables to represent the trigonometric functions of rotor angle in the steady equations of generators, the mathematical model of computing the limit point is transferred into the linear and quadratic functions of unknown variables, and the optimal multiplier Newton method can be used to compute the limit point, and the problem that the Jacobian matrix of the steady equations of the system is singular at the limit point and results in the convergence difficulty is solved. Computations in the IEEE 9-bus system and IEEE 39-bus system
Kind, Dieter
2001-01-01
The second edition of High Voltage Test Techniques has been completely revised. The present revision takes into account the latest international developments in High Voltage and Measurement technology, making it an essential reference for engineers in the testing field.High Voltage Technology belongs to the traditional area of Electrical Engineering. However, this is not to say that the area has stood still. New insulating materials, computing methods and voltage levels repeatedly pose new problems or open up methods of solution; electromagnetic compatibility (EMC) or components and systems al
正离子静电加速器高压电压稳定系统的分析%Analysis of high voltage stability system of positive ion accelerator
Institute of Scientific and Technical Information of China (English)
姜胜南
2001-01-01
对正离子静电加速器的电晕放电法高压电压稳定系统进行了较为细致的分析，同时也分析了另外两种稳压方法：电子枪法和控制喷电电流法。%This article mainly analyzes the corona drain high voltage stability system of the positive ion accelerator, and introduces the other two high voltage stability methods: the electron gun method and the controlling up-charge spray current method.
Linear stability of the Couette flow of a vibrationally excited gas. 2. viscous problem
Grigor'ev, Yu. N.; Ershov, I. V.
2016-03-01
Based on the linear theory, stability of viscous disturbances in a supersonic plane Couette flow of a vibrationally excited gas described by a system of linearized equations of two-temperature gas dynamics including shear and bulk viscosity is studied. It is demonstrated that two sets are identified in the spectrum of the problem of stability of plane waves, similar to the case of a perfect gas. One set consists of viscous acoustic modes, which asymptotically converge to even and odd inviscid acoustic modes at high Reynolds numbers. The eigenvalues from the other set have no asymptotic relationship with the inviscid problem and are characterized by large damping decrements. Two most unstable viscous acoustic modes (I and II) are identified; the limits of these modes were considered previously in the inviscid approximation. It is shown that there are domains in the space of parameters for both modes, where the presence of viscosity induces appreciable destabilization of the flow. Moreover, the growth rates of disturbances are appreciably greater than the corresponding values for the inviscid flow, while thermal excitation in the entire considered range of parameters increases the stability of the viscous flow. For a vibrationally excited gas, the critical Reynolds number as a function of the thermal nonequilibrium degree is found to be greater by 12% than for a perfect gas.
Arkharov, A. M.; Lavrov, N. A.; Romanovskii, V. R.
2014-06-01
The current instability is studied in high-temperature superconducting current-carrying elements with I- V characteristics described by power or exponential equations. Stability analysis of the macroscopic states is carried out in terms of a stationary zero-dimensional model. In linear temperature approximation criteria are derived that allow one to find the maximum allowable values of the induced current, induced electric field intensity, and overheating of the superconductor. A condition is formulated for the complete thermal stabilization of the superconducting composite with regard to the nonlinearity of its I- V characteristic. It is shown that both subcritical and supercritical stable states may arise. In the latter case, the current and electric field intensity are higher than the preset critical parameters of the superconductor. Conditions for these states depending on the properties of the matrix, superconductor's critical current, fill factor, and nonlinearity of the I- V characteristic are discussed. The obtained results considerably augment the class of allowable states for high-temperature superconductors: it is demonstrated that there exist stable resistive conditions from which superconductors cannot pass to the normal state even if the parameters of these conditions are supercritical.
VOLTAGE REGULATORS ASYNCHRONOUS GENERATORS
Directory of Open Access Journals (Sweden)
Grigorash O. V.
2015-06-01
Full Text Available A promising is currently the use of asynchronous generators with capacitive excitation as a source of electricity in stand-alone power systems. Drive asynchronous generators may exercise as a thermal engine and wind wheel wind power plant or turbines of small hydropower plants. The article discusses the structural and schematics of voltage stabilizers and frequency of asynchronous generators with improved operational and technical specifications. Technical novelty of design solutions of the magnetic system and stabilizers asynchronous generator of electricity parameters confirmed by the patents for the invention of the Russian Federation. The proposed technical solution voltage stabilizer asynchronous generators, can reduce the weight of the block capacitors excitation and reactive power compensation, as well as to simplify the control system power circuit which has less power electronic devices. For wind power plants it is an important issue not only to stabilize the voltage of the generator, but also the frequency of the current. Recommend functionality stabilizer schemes parameters of electric power made for direct frequency converters with artificial and natural switching power electronic devices. It is also proposed as part of stabilization systems use single-phase voltage, three-phase transformers with rotating magnetic field, reduce the level of electromagnetic interference generated by power electronic devices for switching, enhance the efficiency and reliability of the stabilizer.
Fairbank, Michael; Li, Shuhui; Fu, Xingang; Alonso, Eduardo; Wunsch, Donald
2014-01-01
We present a recurrent neural-network (RNN) controller designed to solve the tracking problem for control systems. We demonstrate that a major difficulty in training any RNN is the problem of exploding gradients, and we propose a solution to this in the case of tracking problems, by introducing a stabilization matrix and by using carefully constrained context units. This solution allows us to achieve consistently lower training errors, and hence allows us to more easily introduce adaptive capabilities. The resulting RNN is one that has been trained off-line to be rapidly adaptive to changing plant conditions and changing tracking targets. The case study we use is a renewable-energy generator application; that of producing an efficient controller for a three-phase grid-connected converter. The controller we produce can cope with the random variation of system parameters and fluctuating grid voltages. It produces tracking control with almost instantaneous response to changing reference states, and virtually zero oscillation. This compares very favorably to the classical proportional integrator (PI) controllers, which we show produce a much slower response and settling time. In addition, the RNN we propose exhibits better learning stability and convergence properties, and can exhibit faster adaptation, than has been achieved with adaptive critic designs.
Voltage Stability Analysis of Sichuan Power Grid Based on Sensitivity Method%基于灵敏度方法的四川电网的电压稳定分析
Institute of Scientific and Technical Information of China (English)
陈博; 李兴源; 井艳青; 何笠
2011-01-01
四川电网的快速增长，使电压稳定问题成为影响电网稳定的关键因素。介绍了电压稳定灵敏度方法的理论推导，并应用机电暂态仿真程序BPA对四川电网成都地区环网进行节点灵敏度、线路灵敏度以及P-V曲线法等电压稳定分析方法进行了研究，提出了提高电压稳定度的措施，仿真结果表明，利用加入并联补偿的方式可以提高成都地区环网的电压稳定强度。%With the rapid growth of Sichuan power grid, voltage stability will be the key factor influencing the power grid stability. This paper presents theoretical derivation of sensitivity method for voltage stability, then Chengdu power grid is researched by using electromechanical transient simulation program BPA, including the method of node-sensitivity, line-sensitivity and P-V curve, and the measures to improve the voltage stability are proposed. Simulation resuits show that adding parallel compensation could strengthen the voltage stability of Chengdu power grid.
Low Voltage Power Supply Incorporating Ceramic Transformer
Imori, M
2007-01-01
A low voltage power supply provides the regulated output voltage of 1 V from the supply voltage around 48 V. The low voltage power supply incorporates a ceramic transformer which utilizes piezoelectric effect to convert voltage. The ceramic transformer isolates the secondary from the primary, thus providing the ground isolation between the supply and the output voltages. The ceramic transformer takes the place of the conventional magnetic transformer. The ceramic transformer is constructed from a ceramic bar and does not include any magnetic material. So the low voltage power supply can operate under a magnetic field. The output voltage is stabilized by feedback. A feedback loop consists of an error amplifier, a voltage controlled oscillator and a driver circuit. The amplitude ratio of the transformer has dependence on the frequency, which is utilized to stabilize the output voltage. The low voltage power supply is investigated on the analogy of the high voltage power supply similarly incorporating the cerami...
On the use of stability regions in the numerical analysis of initial value problems
Lenferink, H. W. J.; Spijker, M. N.
1991-07-01
This paper deals with the stability analysis of one-step methods in the numerical solution of initial (-boundary) value problems for linear, ordinary, and partial differential equations. Restrictions on the stepsize are derived which guarantee the rate of error growth in these methods to be of moderate size. These restrictions are related to the stability region of the method and to numerical ranges of matrices stemming from the differential equation under consideration. The errors in the one-step methods are measured in arbitrary norms (not necessarily generated by an inner product). The theory is illustrated in the numerical solution of the heat equation and some other differential equations, where the error growth is measured in the maximum norm.
Resonance, Chaos and Stability in the General Three-Body Problem
Mardling, R. A.
2008-05-01
Three-body stability is fundamental to astrophysical processes on all length and mass scales from planetary systems to clusters of galaxies, so it is vital we have a deep and thorough understanding of this centuries-old problem. Here we summarize an analytical method for determining the stability of arbitrary three-body hierarchies which makes use of the chaos theory concept of resonance overlap. For the first time the dependence on all orbital elements and masses can be given explicitly via simple analytical expressions which contain no empirical parameters. For clarity and brevity, analysis in this paper is restricted to coplanar systems including a description of a practical algorithm for use in N-body and other applications. A Fortran routine for arbitrarily inclined systems is available from the author, and animations of stable and unstable systems are available at www.maths.monash.edu.au/~ro/Capri.
Lee, Sanghyun; Wheeler, Mary F.
2017-02-01
We present a novel approach to the simulation of miscible displacement by employing adaptive enriched Galerkin finite element methods (EG) coupled with entropy residual stabilization for transport. In particular, numerical simulations of viscous fingering instabilities in heterogeneous porous media and Hele-Shaw cells are illustrated. EG is formulated by enriching the conforming continuous Galerkin finite element method (CG) with piecewise constant functions. The method provides locally and globally conservative fluxes, which are crucial for coupled flow and transport problems. Moreover, EG has fewer degrees of freedom in comparison with discontinuous Galerkin (DG) and an efficient flow solver has been derived which allows for higher order schemes. Dynamic adaptive mesh refinement is applied in order to reduce computational costs for large-scale three dimensional applications. In addition, entropy residual based stabilization for high order EG transport systems prevents spurious oscillations. Numerical tests are presented to show the capabilities of EG applied to flow and transport.
Adaptive coordinated control of engine speed and battery charging voltage
Institute of Scientific and Technical Information of China (English)
Jiangyan ZHANG; Xiaohong JIAO
2008-01-01
In this paper, the control problem of auxiliary power unit (APU) for hybrid electric vehicles is investigated. An adaptive controller is provided to achieve the coordinated control between the engine speed and the battery charging voltage. The proposed adaptive coordinated control laws for the throttle angle of the engine and the voltage of the power-converter can guarantee not only the asymptotic tracking performance of the engine speed and the regulation of the battery charging voltage, but also the robust stability of the closed loop system under external load changes. Simulation results are given to verify the performance of the proposed adaptive controller.
Pulkkinen, A. A.; Lindahl, S.; Viljanen, A.; Pirjola, R.
2004-12-01
In October 30, 2003, an ongoing geomagnetic superstorm knocked down a part of the high-voltage power transmission system in southern Sweden operated by the Sydkraft company. The blackout lasted for an hour and left about 50000 people without electricity. The incident was probably the most severe GIC failure observed since the well-known March 1989 Québec blackout and thus the problems in a Swedish system deserve a closer look. The geophysical background and the impacts on the Swedish high-voltage power transmission system of the October 29-31, 2003 geomagnetic storm are described in the study at hand. It was seen that athough no serious problems in North-America have been reported, the "three-phase" storm produced exceptionally large geomagnetic activity at the Fennoscandian auroral region. It was also seen that GIC modeled for southern Sweden region using very simplistic methods were able to explain the times of the failures in the Swedish system thus confirming the sources of experienced problems and adding also GIC to the long list of causes of technological impacts of the storm. Though the great diversity of the GIC drivers are addresses in the study, the problems in operating the Swedish system during the exceptionally intense storm of October 29-31, 2003 are attributed geophysically to substorms, SSCs and enhanced ionospheric convection all of which were creating large and complex geoelectric fields capable of driving large GIC. Based on the basic two-fold nature of the failure-related geoelectric field characteristics, a semi-deterministic approach for forecasting GIC-related geomagnetic activity in which average overall activity is supplemented with statistical estimations of the amplitudes of GIC fluctuations is suggested.
Energy Technology Data Exchange (ETDEWEB)
Ferreira, C.A. [Centrais Eletricas Brasileiras S.A. (ELETROBRAS), Rio de Janeiro, RJ (Brazil)], E-mail: carlosaparecido@eletrobras.com; Prada, R.B. [Pontificia Universidade Catolica (PUC-Rio), Rio de Janeiro, RJ (Brazil)], E-mail: prada@ele.puc-rio.br; Costa, V.M. da [Universidade Federal de Juiz de Fora (UFJF), MG (Brazil). Programa de Pos-Graduacao em Engenharia Eletrica], E-mail: vander@lacee.ufjf.br
2009-07-01
This paper addresses the impacts of the world-wide used model of load tap changer transformers - LTCs in voltage stability analysis. Two fundamental questions will be examined: the voltage stability margin and the effect of voltage control actions in the abnormal operation region. It may be easily observed that, in a 2-bus system, the point of collapse and the equivalent impedance which represents the load, will or will not vary, according to the direction of the flow, when the tap is changed. Intuitively, however, it was imagined that this dependence with the flow direction would not occur in a real transformer. It was confirmed through laboratory tests, so it can be concluded that the LCT model, used all over the world, is not adequate to be used in voltage stability analysis. By using the usual model, it is also shown that there are signs that incorrect information regarding voltage control actions can be provided to the operators if the system is operating in the abnormal region. (author)
Zohsel, K; Bianchi, V; Mascheretti, S; Hohm, E; Schmidt, M H; Esser, G; Brandeis, D; Banaschewski, T; Nobile, M; Laucht, M
2015-11-01
Attention problems affect a substantial number of children and adolescents and are predictive of academic underachievement and lower global adaptive functioning. Considerable variability has been observed with regard to the individual development of attention problems over time. In particular, the period of adolescence is characterized by substantial maturation of executive functioning including attentional processing, with the influence of genetic and environmental factors on individual trajectories not yet well understood. In the present investigation, we evaluated whether the monoamine oxidase A functional promoter polymorphism, MAOA-LPR, plays a role in determining continuity of parent-rated attention problems during adolescence. At the same time, a potential effect of severe life events (SLEs) was taken into account. A multi-group path analysis was used in a sample of 234 adolescents (149 males, 85 females) who took part in an epidemiological cohort study at the ages of 11 and 15 years. Attention problems during early adolescence were found to be a strong predictor of attention problems in middle adolescence. However, in carriers of the MAOA-LPR low-activity variant (MAOA-L), stability was found to be significantly higher than in carriers of the high-activity variant (MAOA-H). Additionally, only in MAOA-L carriers did SLEs during adolescence significantly impact on attention problems at the age of 15 years, implying a possible gene × environment interaction. To conclude, we found evidence that attention problems during adolescence in carriers of the MAOA-L allele are particularly stable and malleable to life stressors. The present results underline the usefulness of applying a more dynamic GxE perspective. © 2015 John Wiley & Sons Ltd and International Behavioural and Neural Genetics Society.
Stability of Relative Equilibria in the Planar N-Vortex Problem
Roberts, Gareth E
2013-01-01
We study the linear and nonlinear stability of relative equilibria in the planar N-vortex problem, adapting the approach of Moeckel from the corresponding problem in celestial mechanics. After establishing some general theory, a topological approach is taken to show that for the case of positive circulations, a relative equilibrium is linearly stable if and only if it is a nondegenerate minimum of the Hamiltonian restricted to a level surface of the angular impulse (moment of inertia). Using a criterion of Dirichlet's, this implies that any linearly stable relative equilibrium with positive vorticities is also nonlinearly stable. Two symmetric families, the rhombus and the isosceles trapezoid, are analyzed in detail, with stable solutions found in each case.
Parallel Optimization of Polynomials for Large-scale Problems in Stability and Control
Kamyar, Reza
In this thesis, we focus on some of the NP-hard problems in control theory. Thanks to the converse Lyapunov theory, these problems can often be modeled as optimization over polynomials. To avoid the problem of intractability, we establish a trade off between accuracy and complexity. In particular, we develop a sequence of tractable optimization problems --- in the form of Linear Programs (LPs) and/or Semi-Definite Programs (SDPs) --- whose solutions converge to the exact solution of the NP-hard problem. However, the computational and memory complexity of these LPs and SDPs grow exponentially with the progress of the sequence - meaning that improving the accuracy of the solutions requires solving SDPs with tens of thousands of decision variables and constraints. Setting up and solving such problems is a significant challenge. The existing optimization algorithms and software are only designed to use desktop computers or small cluster computers --- machines which do not have sufficient memory for solving such large SDPs. Moreover, the speed-up of these algorithms does not scale beyond dozens of processors. This in fact is the reason we seek parallel algorithms for setting-up and solving large SDPs on large cluster- and/or super-computers. We propose parallel algorithms for stability analysis of two classes of systems: 1) Linear systems with a large number of uncertain parameters; 2) Nonlinear systems defined by polynomial vector fields. First, we develop a distributed parallel algorithm which applies Polya's and/or Handelman's theorems to some variants of parameter-dependent Lyapunov inequalities with parameters defined over the standard simplex. The result is a sequence of SDPs which possess a block-diagonal structure. We then develop a parallel SDP solver which exploits this structure in order to map the computation, memory and communication to a distributed parallel environment. Numerical tests on a supercomputer demonstrate the ability of the algorithm to
Ford, Kevin J; Davis, Graeme W
2014-10-29
The strength and dynamics of synaptic transmission are determined, in part, by the presynaptic action potential (AP) waveform at the nerve terminal. The ion channels that shape the synaptic AP waveform remain essentially unknown for all but a few large synapses amenable to electrophysiological interrogation. The Drosophila neuromuscular junction (NMJ) is a powerful system for studying synaptic biology, but it is not amenable to presynaptic electrophysiology. Here, we demonstrate that Archaerhodopsin can be used to quantitatively image AP waveforms at the Drosophila NMJ without disrupting baseline synaptic transmission or neuromuscular development. It is established that Shaker mutations cause a dramatic increase in neurotransmitter release, suggesting that Shaker is predominantly responsible for AP repolarization. Here we demonstrate that this effect is caused by a concomitant loss of both Shaker and slowpoke (slo) channel activity because of the low extracellular calcium concentrations (0.2-0.5 mM) used typically to assess synaptic transmission in Shaker. In contrast, at physiological extracellular calcium (1.5 mM), the role of Shaker during AP repolarization is limited. We then provide evidence that calcium influx through synaptic CaV2.1 channels and subsequent recruitment of Slo channel activity is important, in concert with Shaker, to ensure proper AP repolarization. Finally, we show that Slo assumes a dominant repolarizing role during repetitive nerve stimulation. During repetitive stimulation, Slo effectively compensates for Shaker channel inactivation, stabilizing AP repolarization and limiting neurotransmitter release. Thus, we have defined an essential role for Slo channels during synaptic AP repolarization and have revised our understanding of Shaker channels at this model synapse.
Optimal coordinated voltage control of power systems
Institute of Scientific and Technical Information of China (English)
LI Yan-jun; HILL David J.; WU Tie-jun
2006-01-01
An immune algorithm solution is proposed in this paper to deal with the problem of optimal coordination of local physically based controllers in order to preserve or retain mid and long term voltage stability. This problem is in fact a global coordination control problem which involves not only sequencing and timing different control devices but also tuning the parameters of controllers. A multi-stage coordinated control scheme is presented, aiming at retaining good voltage levels with minimal control efforts and costs after severe disturbances in power systems. A self-pattern-recognized vaccination procedure is developed to transfer effective heuristic information into the new generation of solution candidates to speed up the convergence of the search procedure to global optima. An example of four bus power system case study is investigated to show the effectiveness and efficiency of the proposed algorithm, compared with several existing approaches such as differential dynamic programming and tree-search.
Escher, Joachim
2010-01-01
We study a moving boundary problem describing the growth of nonnecrotic tumors in different regimes of vascularisation. This model consists of two decoupled Dirichlet problem, one for the rate at which nutrient is added to the tumor domain and one for the pressure inside the tumor. These variables are coupled by a relation which describes the dynamic of the boundary. By re-expressing the problem as an abstract evolution equation, we prove local well-posedness in the small Hoelder spaces context. Further on, we use the principle of linearised stability to characterise the stability properties of the unique radially symmetric equilibrium of the problem.
Mitigation of Voltage Sags in CIGRE Low Voltage Distribution Network
DEFF Research Database (Denmark)
Mustafa, Ghullam; Bak-Jensen, Birgitte; Mahat, Pukar;
2013-01-01
problems in the distribution system. The voltage problems dealt with in this paper are to show how to mitigate voltage sags in the CIGRE Low Voltage (LV) test network and networks like this. The voltage sags, for the tested cases in the CIGRE LV test network are mainly due to three phase faults....... The compensation of voltage sags in the different parts of CIGRE distribution network is done by using the four STATCOM compensators already existing in the test grid. The simulations are carried out in DIgSILENT power factory software version 15.0....
Indian Academy of Sciences (India)
Pravir Dutt; Satyendra Tomar
2003-11-01
In this paper we show that the ℎ- spectral element method developed in [3,8,9] applies to elliptic problems in curvilinear polygons with mixed Neumann and Dirichlet boundary conditions provided that the Babuska–Brezzi inf-sup conditions are satisfied. We establish basic stability estimates for a non-conforming ℎ- spectral element method which allows for simultaneous mesh refinement and variable polynomial degree. The spectral element functions are non-conforming if the boundary conditions are Dirichlet. For problems with mixed boundary conditions they are continuous only at the vertices of the elements. We obtain a stability estimate when the spectral element functions vanish at the vertices of the elements, which is needed for parallelizing the numerical scheme. Finally, we indicate how the mesh refinement strategy and choice of polynomial degree depends on the regularity of the coefficients of the differential operator, smoothness of the sides of the polygon and the regularity of the data to obtain the maximum accuracy achievable.
Institute of Scientific and Technical Information of China (English)
周红婷; 宋玮
2016-01-01
为了进一步分析大规模风电汇集地区电压稳定性，提出应考虑风电场动态无功控制的影响。基于电压-无功灵敏度法解释了动态无功补偿装置的恒无功控制方式所带来的汇集地区电压上升问题。利用小扰动稳定法，分析出采用高压侧恒电压控制的风电场内动态无功补偿装置之间存在很强的相互作用，并会引起不稳定的电压振荡。以华北某风电汇集地区为例，在PSS/E中比较分析区内所有风电场内动态无功补偿装置分别采用恒无功、高压侧恒电压和低压侧恒电压三种控制方式时受到小扰动后的电压变化。仿真结果验证了分析结论，表明在研究风电汇集地区电压稳定性问题上，考虑风电场的动态无功控制影响是必要的。%In order to analyze voltage stability in large-scale wind farms integration area, this paper proposes that dynamic reactive power control should be considered. Presently, dynamic reactive power compensation device in wind farms widely adopts constant reactive power control. According to it, this paper firstly proposes this control mode of dynamic reactive power compensation device can bring voltage stability problem based on voltage-reactive power sensitivity method;then it uses small signal stability analysis method, consulting that there is a strong interaction between dynamic reactive power compensation devices in wind farms which adopts high-voltage side constant voltage control. As a result, it will lead to unstable high frequency oscillation;finally, taking a wind farm integration area in North China, it obtains the voltage change of all dynamic reactive power compensation device in wind farm after small disturbance when constant control mode, high-voltage side constant voltage control, and low-voltage side constant voltage control are adopted respectively. The result shows that considering dynamic reactive power control is important for voltage stability
Institute of Scientific and Technical Information of China (English)
吴昊; 薛贵挺; 张焰; 杨增辉; 冯煜尧
2011-01-01
Due to the common mode outages and dependent outages have great impact on system static voltage stability,this paper focuses on the establishment of the equivalent branch outage model for two parallel transmission lines by considering outage overlapping, then computes the state probability of transmission system. Basing on the state probability model of power system, a risk index system of static voltage stability and the calculation method of every index are presented. By the voltage stability criteria based on CPF and optimal load shedding model, the loss of voltage stability of transmission system can be judged and controlled. Taking an area of power grid for east china for example, the risk of static voltage stability is assessed, which verifies the effectiveness of the proposed method.%鉴于双回平行输电线路共同模式停运和相关停运对系统电压稳定性影响较大,本文重点建立了双回线多种停运模式重叠的支路等效停运模型,进而计算输电系统状态概率.在输电系统状态概率模型的基础上,提出输电系统静态电压稳定风险评估指标体系及各项指标计算方法,其中通过基于连续潮流的电压稳定性判据及最优切负荷模型,对输电系统电压失稳进行判定及校正控制.最后以华东某地区电网为例进行静态电压稳定风险评估,说明本文所提方法的有效性.
Institute of Scientific and Technical Information of China (English)
傅旭; 付翀丽; 黄明良
2015-01-01
The effect of ZIP load characteristics on node static voltage stability is analyzed in detail. It is pointed out that the constant power component in ZIP load determines the degree of static voltage stability of the node. A new index for voltage stability based on locally measurable quantities considering the load static characteristics is presented. A simple calculation method for calculating the Thevenin equivalent parameter is provided. The proposed index is tested on IEEE 57-bus systems, and the simulation results indicate that this index can correctly reflect the effect of load static characteristics on node voltage stability, and the calculation of the Thevenin equivalent parameter is simple, thus it is suitable for the on-line monitoring of static voltage stability.%详细分析ZIP负荷特性对节点静态电压稳定性的影响规律，指出ZIP负荷中的恒定功率分量决定了该节点的静态电压稳定程度，提出一种基于局部测量的计及负荷静态特性的电压稳定指标，并给出一种简单的计算节点戴维南等值参数的计算方法。IEEE 57节点仿真表明所提指标可以很好地考虑负荷静态特性对节点电压稳定性的影响，并且戴维南等值参数计算简单，适合于静态电压稳定的在线监控。
Stability of multi-objective bi-level linear programming problems under fuzziness
Directory of Open Access Journals (Sweden)
Abo-Sinna Mahmoud A.
2013-01-01
Full Text Available This paper deals with multi-objective bi-level linear programming problems under fuzzy environment. In the proposed method, tentative solutions are obtained and evaluated by using the partial information on preference of the decision-makers at each level. The existing results concerning the qualitative analysis of some basic notions in parametric linear programming problems are reformulated to study the stability of multi-objective bi-level linear programming problems. An algorithm for obtaining any subset of the parametric space, which has the same corresponding Pareto optimal solution, is presented. Also, this paper established the model for the supply-demand interaction in the age of electronic commerce (EC. First of all, the study uses the individual objectives of both parties as the foundation of the supply-demand interaction. Subsequently, it divides the interaction, in the age of electronic commerce, into the following two classifications: (i Market transactions, with the primary focus on the supply demand relationship in the marketplace; and (ii Information service, with the primary focus on the provider and the user of information service. By applying the bi-level programming technique of interaction process, the study will develop an analytical process to explain how supply-demand interaction achieves a compromise or why the process fails. Finally, a numerical example of information service is provided for the sake of illustration.
Hamed, Haikel Ben; Bennacer, Rachid
2008-08-01
This work consists in evaluating algebraically and numerically the influence of a disturbance on the spectral values of a diagonalizable matrix. Thus, two approaches will be possible; to use the theorem of disturbances of a matrix depending on a parameter, due to Lidskii and primarily based on the structure of Jordan of the no disturbed matrix. The second approach consists in factorizing the matrix system, and then carrying out a numerical calculation of the roots of the disturbances matrix characteristic polynomial. This problem can be a standard model in the equations of the continuous media mechanics. During this work, we chose to use the second approach and in order to illustrate the application, we choose the Rayleigh-Bénard problem in Darcy media, disturbed by a filtering through flow. The matrix form of the problem is calculated starting from a linear stability analysis by a finite elements method. We show that it is possible to break up the general phenomenon into other elementary ones described respectively by a disturbed matrix and a disturbance. A good agreement between the two methods was seen. To cite this article: H.B. Hamed, R. Bennacer, C. R. Mecanique 336 (2008).
Linear stability analysis in the numerical solution of initial value problems
van Dorsselaer, J. L. M.; Kraaijevanger, J. F. B. M.; Spijker, M. N.
This article addresses the general problem of establishing upper bounds for the norms of the nth powers of square matrices. The focus is on upper bounds that grow only moderately (or stay constant) where n, or the order of the matrices, increases. The so-called resolvant condition, occuring in the famous Kreiss matrix theorem, is a classical tool for deriving such bounds.Recently the classical upper bounds known to be valid under Kreiss's resolvant condition have been improved. Moreover, generalizations of this resolvant condition have been considered so as to widen the range of applications. The main purpose of this article is to review and extend some of these new developments.The upper bounds for the powers of matrices discussed in this article are intimately connected with the stability analysis of numerical processes for solving initial(-boundary) value problems in ordinary and partial linear differential equations. The article highlights this connection.The article concludes with numerical illustrations in the solution of a simple initial-boundary value problem for a partial differential equation.
Institute of Scientific and Technical Information of China (English)
沈良国; 严祖树; 王钊; 张兴; 赵元富
2007-01-01
A high-accuracy,low-dropout (LDO) voltage regulator is presented.Using the slow-rolloff frequency compensation scheme,the LDO effectively overcomes the stability problem,facilitates the use of a ceramic capacitor,and improves the output voltage accuracy,which is critical for powering high-performance analog circuitry.The slow-rolloff compensation scheme is realized by introducing three pole-zero pairs,including the proposed pole-zero pair and sense zero.The post-layout simulation results demonstrate that this LDO has robust system stability,a high open-loop gain,and a high unit-gain frequency,which lead to excellent regulation and transient response performance.The line and load regulation are 27μV/V and 3.78μV/mA,and the overshoots of the output voltage are less than 30mV,while the dropout voltage is 120mV for a 150mA load current.%提出了LDO,其基于缓慢滚降式频率补偿方法,通过在电路中引入三个极零对(极零对的产生没有增加静态功耗),不仅克服了常规LDO不能使用低等效串联电阻、低成本陶瓷输出电容的缺点,而且确保了系统在整个负载和输入电压变化范围内稳定工作.由于LDO通常给高性能模拟电路供电,因此其输出电压精度至关重要;而该补偿方法能满足高环路增益、高单位增益带宽的设计要求,从而大幅提高LDO的精度.该LDO基于0.5μm CMOS工艺实现.后仿结果表明,即使在低压满负载条件下,其开环DC增益仍高于70dB,满载时单位增益带宽可达3MHz,线性调整率和负载调整率分别为27μV/V和3.78μV/mA,过冲和欠冲电压均小于30mV,负载电流为150mA时的漏失电压(dropout电压)仅为120mV.
Peng, Zhe; Yi, Xiaohui; Liu, Zixuan; Shang, Jie; Wang, Deyu
2016-06-15
Through rational organization of two redox active building block, a triphenylamine-based metal-organic framework (MOF) material, Cu-TCA (H3TCA = tricarboxytriphenyl amine), was synthesized and applied as a cathode active material for the first time in lithium batteries. Cu-TCA exhibited redox activity both in the metal clusters (Cu(+)/Cu(2+)) and organic ligand radicals (N/N(+)) with separated voltage plateaus and a high working potential vs Li/Li(+) up to 4.3 V, comparing with the current commercial LiCoO2 cathode materials. The electrochemical behaviors of this MOF electrode material at different states of charge were carefully studied by cyclic voltammetry, X-ray photoelectron spectroscopy, and photoluminescence techniques. Long cycling stability of this MOF was achieved with an average Coulombic efficiency of 96.5% for 200 cycles at a 2 C rate. Discussing the electrochemical performances on the basis of capacity contributions from the metal clusters (Cu(+)/Cu(2+)) and organic ligands (N/N(+)) proposes an alternative mechanism of capacity loss for the MOF materials used in lithium batteries. This improved understanding will shed light on the designing principle of MOF-based cathode materials for their practical application in battery sciences.
Directory of Open Access Journals (Sweden)
Hiroshi Kikusato
2016-01-01
Full Text Available Many photovoltaic (PV systems have been installed in distribution systems. This installation complicates the maintenance of all voltages within the appropriate range in all low-voltage distribution systems (LVDSs because the trends in voltage fluctuation differ in each LVDS. The installation of a low-voltage regulator (LVR that can accordingly control the voltage in each LVDS has been studied as a solution to this problem. Voltage control in a medium-voltage distribution system must be considered to study the deployment of LVRs. In this study, we installed LVRs in the LVDSs in which the existing voltage-control scheme cannot prevent voltage deviation and performed a numerical simulation by using a distribution system model with PV to evaluate the deployment of the LVRs.
Heat-pump performance: voltage dip/sag, under-voltage and over-voltage
Directory of Open Access Journals (Sweden)
William J.B. Heffernan
2014-12-01
Full Text Available Reverse cycle air-source heat-pumps are an increasingly significant load in New Zealand and in many other countries. This has raised concern over the impact wide-spread use of heat-pumps may have on the grid. The characteristics of the loads connected to the power system are changing because of heat-pumps. Their performance during under-voltage events such as voltage dips has the potential to compound the event and possibly cause voltage collapse. In this study, results from testing six heat-pumps are presented to assess their performance at various voltages and hence their impact on voltage stability.
The troublesome birth of hydrodynamic stability theory: Sommerfeld and the turbulence problem
Eckert, M.
2010-07-01
More than a hundred years ago William McFadden Orr and Arnold Sommerfeld conceived an approach to account for the transition from laminar to turbulent flow in terms of hydrodynamic stability theory. But the “turbulence problem”, as this challenge became notoriously famous, could not be solved by this method. By 1920, it was widely recognized as an outstanding riddle. Although famous theoretical physicists like Werner Heisenberg dedicated a considerable effort to this problem, the “Orr-Sommerfeld method” has never found the attention of historians of science. This article describes its early perception and development in Germany, and how the “turbulence problem” reached center stage after the First World war as a major challenge for theorists with different perspectives.
Local Projection-Based Stabilized Mixed Finite Element Methods for Kirchhoff Plate Bending Problems
Directory of Open Access Journals (Sweden)
Xuehai Huang
2013-01-01
Full Text Available Based on stress-deflection variational formulation, we propose a family of local projection-based stabilized mixed finite element methods for Kirchhoff plate bending problems. According to the error equations, we obtain the error estimates of the approximation to stress tensor in energy norm. And by duality argument, error estimates of the approximation to deflection in H1-norm are achieved. Then we design an a posteriori error estimator which is closely related to the equilibrium equation, constitutive equation, and nonconformity of the finite element spaces. With the help of Zienkiewicz-Guzmán-Neilan element spaces, we prove the reliability of the a posteriori error estimator. And the efficiency of the a posteriori error estimator is proved by standard bubble function argument.
Ridenti, M. A.; Pascholati, P. R.; Gonçalves, J. A. C.; Bueno, C. C.
2015-09-01
The I - ΔV characteristic curve of a well type ionization chamber irradiated with 192Ir sources (0.75 Ci-120 Ci) was fitted using the exact solution of the Thomson problem. The recombination coefficient and saturation current were estimated using this new approach. The saturation current was compared with the results of the conventional method based on Boag-Wilson formula. It was verified that differences larger than 1% between both methods only occurred at activities higher than 55 Ci. We concluded that this new approach is recommended for a more accurate estimate of the saturation current when it is not possible to measure currents satisfying the condition I /Isat > 0.95. From the calibration curve the average value of pairs of carriers created per unit volume was estimated to be equal to η = 8.1 ×10-3cm-3s-1 Bq-1 and from that value it was estimated that ~ 17 pairs were created on average per second for each decay of the source.
Non-iterative Voltage Stability
Energy Technology Data Exchange (ETDEWEB)
Makarov, Yuri V. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Vyakaranam, Bharat [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Hou, Zhangshuan [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Wu, Di [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Meng, Da [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Wang, Shaobu [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Elbert, Stephen T. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Miller, Laurie E. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Huang, Zhenyu [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2014-09-30
This report demonstrates promising capabilities and performance characteristics of the proposed method using several power systems models. The new method will help to develop a new generation of highly efficient tools suitable for real-time parallel implementation. The ultimate benefit obtained will be early detection of system instability and prevention of system blackouts in real time.
Kuchment, Peter
2015-05-10
© 2015, Springer Basel. In the previous paper (Kuchment and Steinhauer in Inverse Probl 28(8):084007, 2012), the authors introduced a simple procedure that allows one to detect whether and explain why internal information arising in several novel coupled physics (hybrid) imaging modalities could turn extremely unstable techniques, such as optical tomography or electrical impedance tomography, into stable, good-resolution procedures. It was shown that in all cases of interest, the Fréchet derivative of the forward mapping is a pseudo-differential operator with an explicitly computable principal symbol. If one can set up the imaging procedure in such a way that the symbol is elliptic, this would indicate that the problem was stabilized. In the cases when the symbol is not elliptic, the technique suggests how to change the procedure (e.g., by adding extra measurements) to achieve ellipticity. In this article, we consider the situation arising in acousto-optical tomography (also called ultrasound modulated optical tomography), where the internal data available involves the Green’s function, and thus depends globally on the unknown parameter(s) of the equation and its solution. It is shown that the technique of (Kuchment and Steinhauer in Inverse Probl 28(8):084007, 2012) can be successfully adopted to this situation as well. A significant part of the article is devoted to results on generic uniqueness for the linearized problem in a variety of situations, including those arising in acousto-electric and quantitative photoacoustic tomography.
Benchmarking of Voltage Sag Generators
DEFF Research Database (Denmark)
Yang, Yongheng; Blaabjerg, Frede; Zou, Zhixiang
2012-01-01
The increased penetration of renewable energy systems, like photovoltaic and wind power systems, rises the concern about the power quality and stability of the utility grid. Some regulations for Low Voltage Ride-Through (LVRT) for medium voltage or high voltage applications, are coming into force...... to guide these grid-connected distributed power generation systems. In order to verify the response of such systems for voltage disturbance, mainly for evaluation of voltage sags/dips, a Voltage Sag Generator (VSG) is needed. This paper evaluates such sag test devices according to IEC 61000 in order...... to provide cheaper solutions to test against voltage sags. Simulation and experimental results demonstrate that the shunt impedance based VSG solution is the easiest and cheapest one for laboratory test applications. The back-to-back fully controlled converter based VSG is the most flexible solution...
Singularly Perturbed Elliptic Problems in the Case of Exchange of Stabilities
Butuzov, V. F.; Nefedov, N. N.; Schneider, K. R.
2001-01-01
We consider the singularly perturbed boundary value problem (Eɛ) ɛ2 Δu=f(u, x, ɛ) for x∈D, {∂u}/{∂n}-λ(x) u=0 for x∈Γ where D⊂R2 is an open bounded simply connected region with smooth boundary Γ, ɛ is a small positive parameter and ∂/∂n is the derivative along the inner normal of Γ. We assume that the degenerate problem (E0) f(u, x, 0)=0 has two solutions ϕ1(x) and ϕ2(x) intersecting in an smooth Jordan curve C located in D such that fu(ϕi(x), x, 0) changes its sign on C for i=1, 2 (exchange of stabilities). By means of the method of asymptotic lower and upper solutions we prove that for sufficiently small ɛ, problem (Eɛ) has at least one solution u(x, ɛ) satisfying α(x, ɛ)⩽u(x, ɛ)⩽β(x, ɛ) where the upper and lower solutions β(x, ɛ) and α(x, ɛ) respectively fulfil β(x, ɛ)-α(x, ɛ)=O(ɛ) for x in a δ-neighborhood of C where δ is any fixed positive number sufficiently small, while β(x, ɛ)-α(x, ɛ)=O(ɛ) for x∈DDδ. In case that f does not depend on ɛ these estimates can be improved. Applying this result to a special reaction system in a nonhomogeneous medium we prove that the reaction rate exhibits a spatial jumping behavior.
Kaur, Gurjot; Pinggera, Alexandra; Ortner, Nadine J; Lieb, Andreas; Sinnegger-Brauns, Martina J; Yarov-Yarovoy, Vladimir; Obermair, Gerald J; Flucher, Bernhard E; Striessnig, Jörg
2015-08-21
L-type voltage-gated Ca(2+) channels (LTCCs) regulate many physiological functions like muscle contraction, hormone secretion, gene expression, and neuronal excitability. Their activity is strictly controlled by various molecular mechanisms. The pore-forming α1-subunit comprises four repeated domains (I-IV), each connected via an intracellular linker. Here we identified a polybasic plasma membrane binding motif, consisting of four arginines, within the I-II linker of all LTCCs. The primary structure of this motif is similar to polybasic clusters known to interact with polyphosphoinositides identified in other ion channels. We used de novo molecular modeling to predict the conformation of this polybasic motif, immunofluorescence microscopy and live cell imaging to investigate the interaction with the plasma membrane, and electrophysiology to study its role for Cav1.2 channel function. According to our models, this polybasic motif of the I-II linker forms a straight α-helix, with the positive charges facing the lipid phosphates of the inner leaflet of the plasma membrane. Membrane binding of the I-II linker could be reversed after phospholipase C activation, causing polyphosphoinositide breakdown, and was accelerated by elevated intracellular Ca(2+) levels. This indicates the involvement of negatively charged phospholipids in the plasma membrane targeting of the linker. Neutralization of four arginine residues eliminated plasma membrane binding. Patch clamp recordings revealed facilitated opening of Cav1.2 channels containing these mutations, weaker inhibition by phospholipase C activation, and reduced expression of channels (as quantified by ON-gating charge) at the plasma membrane. Our data provide new evidence for a membrane binding motif within the I-II linker of LTCC α1-subunits essential for stabilizing normal Ca(2+) channel function. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.
Wang, Yun-Hsiang; Liang, Yung C.; Samudra, Ganesh S.; Huang, Chih-Fang; Kuo, Wei-Hung; Lo, Guo-Qiang
2016-06-01
In this paper, a normally-off AlGaN/GaN MIS-HEMT with improved threshold voltage (VTH) thermal stability is reported with investigations on its physical mechanism. The normally-off operation of the device is achieved from novel short argon plasma treatment (APT) prior to the fluorine plasma treatment (FPT) on Al2O3 gate dielectrics. For the MIS-HEMT with FPT only, its VTH drops from 4.2 V at room temperature to 0.5 V at 200 °C. Alternatively, for the device with APT-then-FPT process, its VTH can retain at 2.5 V at 200 °C due to the increased amount of deep-level traps that do not emit electrons at 200 °C. This thermally stable VTH makes this device suitable for high power applications. The depth profile of the F atoms in Al2O3, measured by the secondary ion mass spectroscopy, reveals a significant increase in the F concentration when APT is conducted prior to FPT. The X-ray photoelectron spectroscopy (XPS) analysis on the plasma-treated Al2O3 surfaces observes higher composition of Al-F bonds if APT was applied before FPT. The enhanced breaking of Al-O bonds due to Ar bombardment assisted in the increased incorporation of F radicals at the surface during the subsequent FPT process. The Schrödinger equation of Al2OxFy cells, with the same Al-F compositions as obtained from XPS, was solved by Gaussian 09 molecular simulations to extract electron state distribution as a function of energy. The simulation results show creation of the deeper trap states in the Al2O3 bandgap when APT is used before FPT. Finally, the trap distribution extracted from the simulations is verified by the gate-stress experimental characterization to confirm the physical mechanism described.
Xia, Hong; Luo, Zhendong
2017-01-01
In this study, we devote ourselves to establishing a stabilized mixed finite element (MFE) reduced-order extrapolation (SMFEROE) model holding seldom unknowns for the two-dimensional (2D) unsteady conduction-convection problem via the proper orthogonal decomposition (POD) technique, analyzing the existence and uniqueness and the stability as well as the convergence of the SMFEROE solutions and validating the correctness and dependability of the SMFEROE model by means of numerical simulations.
Indian Academy of Sciences (India)
V Ganesh; M Subbiah
2009-02-01
For the extended Taylor–Goldstein problem of hydrodynamic stability governing the stability of shear flows of an inviscid, incompressible but density stratified fluid in sea straits of arbitrary cross-section a new estimate for the growth rate of an arbitrary unstable normal mode is given for a class of basic flows. Furthermore the Howard’s conjecture, namely, the growth rate $kc_i→ 0$ as the wave number $k→∞$ is proved for two classes of basic flows.
Institute of Scientific and Technical Information of China (English)
郭亮; 任正某; 湛涛
2012-01-01
A method to enhance the transient voltage stability of wind farm based on doubly-fed induction generator by using SVG is introduced. The doubly-fed induction generator model and static var generator model are implemented in the power system simulation program DlgSILENT/PowerFactory. The contribution to the transient voltage stability is verified by power system simulation .According to the simulation results, it can be concluded that SVG provides reactive power support to the voltage recovery of generators, the voltage restore rapidly after the faults cleared, so the low voltage ride through（LVRT） capability is improved, the continuous operation of wind turbines and the security and stability of the power network are ensured.%研究了用静止无功发生器（SVG）改善基于双馈感应发电机组的风电场的暂态电压稳定性。在DIgSILENT／PowerFactory中建立了双馈感应发电机组及SVG控制模型，通过包含风电场的电力系统仿真，验证了SVG对风电场暂态电压稳定性的作用。仿真结果表明，sVG能够有效地帮助风电场在电网发生故障后迅速恢复电压，提高风电场的故障穿越能力，确保风电机组连续运行及电网安全稳定。
DEFF Research Database (Denmark)
Bieniasz, Leslaw K.; Østerby, Ole; Britz, Dieter
1995-01-01
The stepwise numerical stability of the classic explicit, fully implicit and Crank-Nicolson finite difference discretizations of example diffusional initial boundary value problems from electrochemical kinetics has been investigated using the matrix method of stability analysis. Special attention...
Zhou, Qinglong; Long, Yiming
2017-04-01
In this paper, we consider the elliptic collinear solutions of the classical n-body problem, where the n bodies always stay on a straight line, and each of them moves on its own elliptic orbit with the same eccentricity. Such a motion is called an elliptic Euler-Moulton collinear solution. Here we prove that the corresponding linearized Hamiltonian system at such an elliptic Euler-Moulton collinear solution of n-bodies splits into (n-1) independent linear Hamiltonian systems, the first one is the linearized Hamiltonian system of the Kepler 2-body problem at Kepler elliptic orbit, and each of the other (n-2) systems is the essential part of the linearized Hamiltonian system at an elliptic Euler collinear solution of a 3-body problem whose mass parameter is modified. Then the linear stability of such a solution in the n-body problem is reduced to those of the corresponding elliptic Euler collinear solutions of the 3-body problems, which for example then can be further understood using numerical results of Martínez et al. on 3-body Euler solutions in 2004-2006. As an example, we carry out the detailed derivation of the linear stability for an elliptic Euler-Moulton solution of the 4-body problem with two small masses in the middle.
Institute of Scientific and Technical Information of China (English)
丁涛; 董柏峰; 顾伟; 万秋兰
2013-01-01
紧急状况下，优化包含动态负荷的系统切负荷量，以保证系统电压快速恢复正常状态是系统安全的关键。利用PMU测量信息推导了电压稳定动态线性化指标的灵敏度，将其作为实施切负荷的作用因子。建立了以切负荷量最小为目标函数和电压指标偏差量为约束条件的切负荷优化模型。首次实现了分区多步切负荷的算法，在实时计算得到的动态电压稳定指标超标基础上，利用所提出的优化模型实施多步动态优化切负荷，并实时修正作用因子的灵敏度，克服了传统一步欠切或过切的缺点。用IEEE14节点测试系统和国内实际电网算例证实了该方法的可行性和有效性。%It is critical to guarantee the system’s security as quickly as possible by optimizing the shedding load including dynamic components under contingencies. Dynamic voltage stability linearized index sensitivity for dynamic load model is derived based on PMU for the role of the implementation of load shedding factor;the optimization model of load shedding has been established with the objective function of a minimum of load shedding and the constraint of the voltage indicator deviation. The distributed multi-step load shedding algorithm is firstly achieved according to the dynamic order of the index-exceeding node, and the sensitivity of linearized index is corrected at each step, which overcomes the over-shedding or under-shedding problem in traditional methods. Examples of IEEE 14-bus tested system and real grid system demonstrate the feasibility and effectiveness of this method. This work is supported by National Natural Science Foundation of China (No. 50907008 and No. 60974036).
Shadid, J. N.; Smith, T. M.; Cyr, E. C.; Wildey, T. M.; Pawlowski, R. P.
2016-09-01
A critical aspect of applying modern computational solution methods to complex multiphysics systems of relevance to nuclear reactor modeling, is the assessment of the predictive capability of specific proposed mathematical models. In this respect the understanding of numerical error, the sensitivity of the solution to parameters associated with input data, boundary condition uncertainty, and mathematical models is critical. Additionally, the ability to evaluate and or approximate the model efficiently, to allow development of a reasonable level of statistical diagnostics of the mathematical model and the physical system, is of central importance. In this study we report on initial efforts to apply integrated adjoint-based computational analysis and automatic differentiation tools to begin to address these issues. The study is carried out in the context of a Reynolds averaged Navier-Stokes approximation to turbulent fluid flow and heat transfer using a particular spatial discretization based on implicit fully-coupled stabilized FE methods. Initial results are presented that show the promise of these computational techniques in the context of nuclear reactor relevant prototype thermal-hydraulics problems.
Collision Index and Stability of Elliptic Relative Equilibria in Planar {n} -body Problem
Hu, Xijun; Ou, Yuwei
2016-06-01
It is well known that a planar central configuration of the {n} -body problem gives rise to solutions where each particle moves on a specific Keplerian orbit while the totality of the particles move on a homographic motion. When the eccentricity {e} of the Keplerian orbit belongs in {[0,1)} , following Meyer and Schmidt, we call such solutions elliptic relative equilibria (shortly, ERE). In order to study the linear stability of ERE in the near-collision case, namely when {1-e} is small enough, we introduce the collision index for planar central configurations. The collision index is a Maslov-type index for heteroclinic orbits and orbits parametrised by half-lines that, according to the definition given by Hu and Portaluri (An index theory for unbounded motions of Hamiltonian systems, Hu and Portaluri (2015, preprint)), we shall refer to as half-clinic orbits and whose definition in this context, is essentially based on a blow up technique in the case {e=1} . We get the fundamental properties of collision index and approximation theorems. As applications, we give some new hyperbolic criteria and prove that, generically, the ERE of minimal central configurations are hyperbolic in the near-collision case, and we give a detailed analysis of Euler collinear orbits in the near-collision case.
Keller, Jürgen U.
2008-12-01
The application of concepts, principles, and methods of thermodynamics of equilibria and processes to bioengineering systems has led to a new and growing field: engineering biothermodynamics. This article, which is meant as the first in a series, gives an outline of basic aspects, changes, and actual examples in this field. After a few introductory remarks, the basic concepts and laws of thermodynamics extended to systems with internal variables, which serve as models for biofluids and other biosystems, are given. The method of thermodynamics is then applied to the problem of thermal stability of aqueous protein solutions, especially to that of myoglobin solutions. After this, the phenomenon of hydration of proteins by adsorption and intrusion of water molecules is considered. Several other phenomena like the adsorption of proteins on solid surfaces or cell membranes and their temperature and pressure-related behavior represented by an equation of state, or the thermodynamics of bacterial solutions including chemical reactions like wine fermentation, etc., will be presented in Parts II and III of this article.
Voltage Swells Improvement in Low Voltage Network Using Dynamic Voltage Restorer
Directory of Open Access Journals (Sweden)
R. Omar
2011-01-01
Full Text Available Problem statement: Voltage disturbances are the most common power quality problem due to the increased use of a large numbers of sophisticated electronic equipment in industrial distribution system. The voltage disturbances such as voltage sags, swells, harmonics, unbalance and flickers. High quality in the power supply is needed, since failures due to such disturbances usually have a high impact on production cost. There are many different solutions to compensate voltage disturbances but the use of a DVR is considered to be the most cost effective method. The objective of this study is to propose a new topology of a DVR in order to mitigate voltage swells using a powerful power custom device namely the Dynamic Voltage Restorer (DVR. Approach: New configuration of a DVR with an improvement of a controller based on direct-quadrature-zero method has been introduced to compensate voltage swells in the network. Results: The effectiveness of the DVR with its controller were verify using Matlab/Simulinks SimPower Toolbox and then implemented using 5KVA DVR experimental setup. Simulations and experimental results demonstrate the effective dynamic performance of the proposed configuration. Conclusion: The implimentation of the proposed DVR validate the capabilities in mitigating of voltage swells effectiveness.During voltage swells, the DVR injects an appropriate voltage to maintain the load voltage at its nominal value.
Institute of Scientific and Technical Information of China (English)
姚融融; 李纲园
2014-01-01
To improve the performance of the power, increase the ability of the power to adapt to changes in load, this paper will be designed a power supply system that is built with switch the voltage source and the switch current source in parallel.System uses the output current proportional allocation method at the voltage source and current source in parallel, the problem of output instability is solved af-ter the parallel switching power supply system, the actual parallel power system is constructed.Experi-ments show that this current is automatically allocated pro rata method, can achieve the stability of the power system output power.%为了改善电源的性能，提高电源对变化负载的适应能力，设计将开关电压源和开关电流源并联构建供电系统。系统采用电压源与电流源在输出端并联后按比例分配输出电流的方法，解决开关电源并联后供电系统输出不稳定的问题，构建了实际的并联电源系统。实验表明，采用该文的按比例自动分配电流的方法，可以实现电源系统的大功率稳定输出。
Institute of Scientific and Technical Information of China (English)
杨维满; 王兴贵
2013-01-01
The influences of photovoltaic micro-source characteristics on voltage stability of the series micro-grids (SMGs), whose inverters are connected in series, are analyzed. Firstly the system architecture of SMGs is analyzed; then a photovoltaic array model under complex environment is established and the relations between output voltage of SMGs and micro-source dc link voltages are discussed; finally the influencing mechanism of micro-source characteristics on output voltage of SMGs is analyzed in detail, and a voltage stability control strategy of SMGs based on hybrid energy storage is researched. The validity of the proposed control strategy is verified by results of simulation and experiments.%针对微源逆变器串联连接的微网系统，分析了光伏微源特性对串联型微网(series micro-grids，SMGs)系统电压稳定性的影响。首先分析了系统结构；其次建立了复杂环境条件下光伏阵列模型，讨论了各微源直流链电压与系统输出电压之间的关系；最后分析了微源特性对 SMGs 输出电压的影响机理，并研究了基于混合储能的稳定性控制策略。算例结果验证了该控制策略的有效性。
Hornman, Jorijn; de Winter, Andrea F.; Kerstjens, Jorien M.; Bos, Arend F.; Reijneveld, Sijmen A.
Objective To assess the stability of developmental problems in moderately-late preterm-born children compared with early preterm and full term-born children before school entry at age 4 years and 1 year after school entry at age 5 years. Study design We included 376 early preterm, 688 born
Hornman, Jorijn; de Winter, Andrea F; Kerstjens, Jorien M; Bos, Arend F; Reijneveld, Sijmen A
OBJECTIVE: To assess the stability of developmental problems in moderately-late preterm-born children compared with early preterm and full term-born children before school entry at age 4 years and 1 year after school entry at age 5 years. STUDY DESIGN: We included 376 early preterm, 688 born
Institute of Scientific and Technical Information of China (English)
李晔; 张保会
2016-01-01
Voltages and frequencies have mutual influences after large disturbance. The conventional under-voltage load shedding (UVLS) and under-frequency load shedding (UFLS) are adjusted respectively without full considerations on the time-space distribution character of voltages and the influences of induction motors on the system stability. From the two-node equivalent model, the influence of the slip ratio of the induction motor on transient voltage stability and load stability is analyzed, and a novel index of transient voltage instability which is composed of voltage drop and slip ratio increment is proposed. Furthermore, a wide area measurement system (WAMS) based adaptive load shedding scheme which is constructed by employing the novel index to determine the locations and magnitude of load curtailments is provided. This new scheme includes two control patterns including all nodes load shedding and partial nodes load shedding and it measures the transient voltage stability degree of the system more fully by using the novel index. Simulations on IEEE 39-bus system verify the effectiveness and the superiority of the proposed scheme on guaranteeing the voltage stability and frequency stability after large disturbance, comparing with the conventional control scheme.%频率和电压响应在大扰动后相互耦合,传统的低频、低压减载方案相互独立,未充分考虑电压的时空分布特性和感应电动机对系统稳定性的影响.从2节点系统出发,分析感应电动机转差率偏差值对负荷稳定性和暂态电压稳定性的影响,提出综合考虑感应电动机转差率偏差值和负荷母线电压跌落幅度的暂态电压失稳程度新指标;并基于广域信息条件,利用新指标选择切负荷地点,确定相应控制量以构建新的紧急切负荷方案.该方案利用新指标更加全面地衡量了系统暂态电压稳定程度,具有全网切负荷和局部切负荷两种控制模式.通过IEEE 39节点系统的仿真,
稳压装置在引信保险机构中的应用%Application of Stabilized Voltage Device in Fuze Insurance Mechanism
Institute of Scientific and Technical Information of China (English)
金浩; 曲家惠; 岳明凯
2011-01-01
对于火箭弹来说，引信解除保险可利用的环境力极其有限，其中，利用燃气动力作为引信第二环境力解除保险是目前众多科研工作者研究的一项重要内容。然而，对于不同的火箭弹，其火箭发动机燃烧室可提供的燃气压力是不同的，因此，燃气动力解除保险执行机构的设计也必须针对不同弹种进行，其通用化程度很低。本文设计了一种稳压装置并制作出该装置实验模型样机，通过MAF风洞实验证明了该方案的可行性，为众多科研工作者提供了一个可行的思路。%For rocket projectile, it is extremely limited to remove the fuze insurance by means of environmental force. In which, to use gas power as second environmental force of fuze to remove the insurance is an important research content that the numerous researchers are studied in it. However, for different rocket projectile, the fuel gas pressure provided by its rocket engine combustion chamber is different, accordingly the design of insurance actuator by gas dynamic remove must also be designed to aim at different species, and the degree of its generalization is very low. This paper proposed that it designed a voltage stabilizer, and made the device of experimental MAF prototype. Through the test of experimental model wind tunnel, it validated the feasibility of this scheme. It provides a feasible thinking for scientific research.
PSO-Based Voltage Control Strategy for Loadability Enhancement in Smart Power Grids
Directory of Open Access Journals (Sweden)
Heng-Yi Su
2016-12-01
Full Text Available This paper proposes a new voltage control methodology using the particle swarm optimization (PSO technique for smart grid loadability enhancement. The goal of this paper is to achieve reliable and efficient voltage profile/stability regulation in power grids. This methodology is based on the decouple power flow equations and the worst-case design technique. Specifically, the secondary voltage control (SVC problem is formulated as an L-infinity norm minimization problem which considers overall load voltage deviations in electrical power systems as an objective model, and the PSO technique is employed to determine a robust control action which aims to improve voltage profile and to enlarge transmission grid loadability by optimal coordinated control of VAR sources. The methodology was successfully tested on several IEEE benchmark systems.
Indian Academy of Sciences (India)
H Dattu; M Subbiah
2015-09-01
We consider the linear stability problem of inviscid, incompressible swirling flows with radius-dependent density with respect to two-dimensional disturbances. Some results of Miles on the parallel flow stability theory are extended to the swirling flow stability theory. In particular, series solutions for the stability equation for swirling flows are obtained and these solutions are used in the study of the variation of the Reynolds stress. For singular neutral modes it is shown that the Reynolds stress varies like the inverse square of the radial distance in agreement with the homogeneous flow result of Maslowe & Nigam. It is also proved that singular neutral modes do not exist whenever the value of the Richardson number at the critical layer exceeds one quarter.
Xu, XiaoLong; Deng, SiXu; Wang, Hao; Liu, JingBing; Yan, Hui
2017-04-01
High-voltage lithium-ion batteries (HVLIBs) are considered as promising devices of energy storage for electric vehicle, hybrid electric vehicle, and other high-power equipment. HVLIBs require their own platform voltages to be higher than 4.5 V on charge. Lithium nickel manganese spinel LiNi0.5Mn1.5O4 (LNMO) cathode is the most promising candidate among the 5 V cathode materials for HVLIBs due to its flat plateau at 4.7 V. However, the degradation of cyclic performance is very serious when LNMO cathode operates over 4.2 V. In this review, we summarize some methods for enhancing the cycling stability of LNMO cathodes in lithium-ion batteries, including doping, cathode surface coating, electrolyte modifying, and other methods. We also discuss the advantages and disadvantages of different methods.
Arpaia, Pasquale; Baccigalupi, Carlo; Martino, Michele
2015-09-01
An improved analogue front-end for measuring the high state of trapezoidal voltage pulses with transition duration of 3 μs is presented. A new measurement system, composed by a front-end and the state-of-the-art acquisition board NI PXI-5922, has been realized with improved Common Mode Rejection Ratio (CMRR) of more than 87 dB at DC and 3-sigma stability of ±0.65 ppm over 1 day. After highlighting the main design enhancements with respect to state-of-the-art solutions, the CMRR measurement is reported. The output drift due to temperature and humidity is assessed to be negligible. Finally, the worst-case repeatability is measured both with shorted-to-ground inputs and with an applied common-mode voltage of 10 V, which represents the nominal working condition.
AUTHOR|(SzGeCERN)712364; Arpaia, Pasquale; Martino, Michele
2015-01-01
An improved analogue front-end for measuring the high state of trapezoidal voltage pulses with transition duration of 3 μs is presented. A new measurement system, composed by a front-end and the state-of-the-art acquisition board NI PXI-5922, has been realized with improved Common Mode Rejection Ratio (CMRR) of more than 87 dB at DC and 3-sigma stability of }0.65 ppm over 1 day. After highlighting the main design enhancements with respect to state-of-the-art solutions, the CMRR measurement is reported. The output drift due to temperature and humidity is assessed to be negligible. Finally, the worst-case repeatability is measured both with shorted-to-ground inputs and with an applied common-mode voltage of 10 V, which represents the nominal working condition.
The problem of low voltage during the rural irrigation and prevention measures%浅谈农村灌溉期间低电压问题及预控措施
Institute of Scientific and Technical Information of China (English)
李明
2016-01-01
随着社会生产力的发展，电能逐渐成为农业生产中不可或缺的生产要素。农村在灌溉期间，灌溉负荷会在短时间内剧增，导致供电企业电压供电能量剧增。还容易出现低电压问题，线路过载和电压过低一方面会损坏供电设施，加快供电线路老化，还会烧坏水泵，因此灌溉期低电压成了急需解决的问题。%With thedevelopment of social productive forces,electric energy has gradually become an indispensable element of production in agricultural production. During the irrigation period,the irrigation load will increase sharply in a short time, which will lead to the increase of the power supply voltage of the power supply enterprise.Also prone to the problem of low voltage, line overload and voltage is too low will damage to the power supply facilities, accelerate the aging of the power supply line,it will burn out the pump,so irrigation period of low voltage into the urgent need to solve the problem.
Energy Technology Data Exchange (ETDEWEB)
Kim, Yoongu [ORNL; Dudney, Nancy J [ORNL; Chi, Miaofang [ORNL; Martha, Surendra K [ORNL; Nanda, Jagjit [ORNL; Veith, Gabriel M [ORNL; Liang, Chengdu [ORNL
2013-01-01
High voltage Li-ion cathodes push the limits of stability for both cathode and electrolyte. Here subnanometer coatings of an amorphous thin film electrolyte (Lipon) improved the room temperature and 60 C cycling stability of a LiMn1.5Ni0.5O4 spinel cathode when charged to 4.9V with a standard LiPF6 carbonate electrolyte. The cathodes delivered superior C-rate performances up to a 5C discharge, when compared to the uncoated cathodes. Enhanced performance extended for at least 100 cycles. Electrochemical impedance spectroscopy indicates that Lipon slows the increase of interface resistance. Thicker 1-3nm Lipon coatings are sufficiently insulating as to block electronic transport to the cathode particles. Thick coatings also slow Mn dissolution. Results suggest that Lipon may act to scavenge impurities or block active sites that promote electrolyte decomposition. While greatly improved by the Lipon coating, this cathode is not sufficiently stable for long cycle life applications. Further work is needed to assess if and what surface coatings will ultimately stabilize the high voltage cathodes. Comments include insight from other studies of Lipon coated cathodes and directions for future research.
Directory of Open Access Journals (Sweden)
Naser Parhizgar
2012-02-01
Full Text Available This study starts from the proof of Low Frequency Oscillation (LFO and then points out that there are many ways to study the LFO including its rejection measures. Also in this study one control system is planned in order to regulate voltage at common coupling point (PCC in where STATCOM is installed. This research present a single-machine infinite-bus system with one static synchronous compensator (STATCOM asymmetrically installed as a current source. Together with a classical generator model, the simplest power equation is obtained to give direct and clear physical concepts on synchronizing and damping torque factors. According to the primary equations, some basic issues, such as the relationship of voltage gain control and damping control, operating conditions, and the installation of STATCOM, are investigated in this research. Then, with assistance of proportional controller for voltage regulation and damp control, the digital simulation indicate the necessity of control of STATCOM in damping power system oscillations and supplying regulated voltage support.
Roselyn, J. Preetha; Devaraj, D.; Dash, Subhransu Sekhar
2013-11-01
Voltage stability is an important issue in the planning and operation of deregulated power systems. The voltage stability problems is a most challenging one for the system operators in deregulated power systems because of the intense use of transmission line capabilities and poor regulation in market environment. This article addresses the congestion management problem avoiding offline transmission capacity limits related to voltage stability by considering Voltage Security Constrained Optimal Power Flow (VSCOPF) problem in deregulated environment. This article presents the application of Multi Objective Differential Evolution (MODE) algorithm to solve the VSCOPF problem in new competitive power systems. The maximum of L-index of the load buses is taken as the indicator of voltage stability and is incorporated in the Optimal Power Flow (OPF) problem. The proposed method in hybrid power market which also gives solutions to voltage stability problems by considering the generation rescheduling cost and load shedding cost which relieves the congestion problem in deregulated environment. The buses for load shedding are selected based on the minimum eigen value of Jacobian with respect to the load shed. In the proposed approach, real power settings of generators in base case and contingency cases, generator bus voltage magnitudes, real and reactive power demands of selected load buses using sensitivity analysis are taken as the control variables and are represented as the combination of floating point numbers and integers. DE/randSF/1/bin strategy scheme of differential evolution with self-tuned parameter which employs binomial crossover and difference vector based mutation is used for the VSCOPF problem. A fuzzy based mechanism is employed to get the best compromise solution from the pareto front to aid the decision maker. The proposed VSCOPF planning model is implemented on IEEE 30-bus system, IEEE 57 bus practical system and IEEE 118 bus system. The pareto optimal
Actual problems of the capital stability management in the Ukraine’s banking system
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Svitlana Yehorycheva
2017-06-01
Full Text Available Capital stability of the banking system is the basis of its effective development and realization of its main function – optimal redistribution of capital. So, the aim of the article is to develop indicators of capital stability of the banking system, and to propose the frameworks for the long term capital stability strategy of the banking system in Ukraine. For this purpose, the analysis of micro- and macroeconomic indicators of the capital stability of domestic banks within the period 2007–2016 is made. To carry out the research, there were used the statistic data of the National Bank of Ukraine, its legislative and regulatory documents, the Basel Accords. Capital stability of the banking system has been defined in the article as the process of ensuring capitalization that is adequate to the banking risks and cyclical economic development. It has been detected that a significant reduction in return on equity of the Ukrainian banks in 2014–2015 even with restoring their liquidity has had a crucial destabilizing impact on their capital stability. In order to improve the assessment of capital stability, its key indicators for the groups of domestic banks have been studied. The necessity of refocusing macroprudential requirements of the National Bank of Ukraine from quantitative indicators to qualitative ones to ensure economic development has been proved. It has been concluded that a necessary condition for restoring the Ukrainian banking system was to develop an effective strategy for ensuring its capital stability, which should be focused on the creation of its diversified structure.
Institute of Scientific and Technical Information of China (English)
刘彦呈; 王川; 魏一
2011-01-01
A dynamic eigen analysis method is presented aiming at the defects that current voltage stability research results cannot give the explicit criterion about transient voltage stability information. First, this paper establishes an integrated mathematical model reflecting power system transient process with the consideration of speed-adjusting and excitation-control, i.e., Non-linear Differential Algebraic Equations (NDAE). Second, all the eigen values and left, right eigen vectors are solved by using implicit trapezoidal integration method to build Jacobian matrix dynamically in the process of step-by-step integration of NDAE. Finally, this paper calculates all the participating factors of eigen vectors corresponding with all status variables. Then, transient voltage instability criterion is proposed. Simulation results after comparing the method with time domain simulation demonstrate that the transient voltage instability criterion is correct. The paper provides a novel way to research power system transient voltage stability in terms of combining linear system theory with numerical integration.This work is supported by Natural Science Foundation of Liaoning Province (No. 20092148).%针对目前电力系统电压稳定性研究成果难以给出明确的暂态稳定判定信息的缺陷,提出一种电力系统大扰动下暂态电压稳定的动态特征分析方法.该方法首先建立反映电力系统暂态过渡过程的计及调速与励磁控制的综合数学模型,即非线性微分代数方程组(Non-linear Differential Algebraic Equations,NDAE);其次在运用隐式梯形积分法对NDAE进行逐步积分过程中动态生成Jacobian矩阵,并求解出全部特征根及左,右特征向量;最后计算出各个状态变量与之对应特征向量的相关因子,基于此给出暂态电压失稳的判据.该方法通过与时域仿真法的对比结果证明所提出系统暂态电压失稳判据的正确性,为今后从线性系统理论与数值积分
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Muhammad H. Al-Malack
2016-07-01
Full Text Available Fuel oil flyash (FFA produced in power and water desalination plants firing crude oils in the Kingdom of Saudi Arabia is being disposed in landfills, which increases the burden on the environment, therefore, FFA utilization must be encouraged. In the current research, the effect of adding FFA on the engineering properties of two indigenous soils, namely sand and marl, was investigated. FFA was added at concentrations of 5%, 10% and 15% to both soils with and without the addition of Portland cement. Mixtures of the stabilized soils were thoroughly evaluated using compaction, California Bearing Ratio (CBR, unconfined compressive strength (USC and durability tests. Results of these tests indicated that stabilized sand mixtures could not attain the ACI strength requirements. However, marl was found to satisfy the ACI strength requirement when only 5% of FFA was added together with 5% of cement. When the FFA was increased to 10% and 15%, the mixture’s strength was found to decrease to values below the ACI requirements. Results of the Toxicity Characteristics Leaching Procedure (TCLP, which was performed on samples that passed the ACI requirements, indicated that FFA must be cautiously used in soil stabilization.
Masoud, Akram; Rahoma, Walid Ali; Abd El-Salam, Fawzy
2016-07-01
My subject of study is the point L1 with oblate and triaxial primaries in the elliptic restricted three-body problem (ERTBP). The study contains a mathematical determination of the location of this point in the form of a power series in the mass ratio and a discussion of its stability. The difference between the location of L1 in the perturbed ERTBP and in the classical circular restricted three-body problem (CRTBP) is graphically represented versus the mass ratio. To study the effect of a small displacement, a test particle is assumed to be subjected in the location of L1.
Milgram, A
2011-02-21
This comment addresses critics on the claimed stability of solution to the accelerated-predator-satiety Lotka-Volterra predator-prey problem, proposed by Dubey al. (2010. A solution to the accelerated-predator-satiety Lotka-Volterra predator-prey problem using Boubaker polynomial expansion scheme. Journal of Theoretical Biology 264, 154-160). Critics are based on incompatibilities between the claimed asymptotic behavior and the presumed Malthusian growth of prey population in absence of predator. Copyright Â© 2010 Elsevier Ltd. All rights reserved.
Institute of Scientific and Technical Information of China (English)
Deng Yinbin; Yang Fen
2008-01-01
This article is contributed to the Cauchy problem u/t = △u + K(ㄧxㄧ)up in Rn x (0,T), u(x,0) =(ψ)(x) in Rn; with initial function(ψ)≠0. The stability of positive radial steady state, which are positive solutions of △u + K(ㄧxㄧ)up =0, is obtained when p is critical for general K(ㄧxㄧ).
Implementation of Line Stability Index for Contingency Analysis and Screening in Power Systems
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Vivek Kumar
2012-01-01
Full Text Available Problem statement: Estimating the margin in the loadability of the power system is essential in the real time voltage stability assessment. Voltage stability is currently one of the most important research areas in the field of electrical power system. In power system operation unpredictable events is termed as contingency and may be caused by line outage in the system which could lead to entire system instability. Voltage stability analysis and contingency analysis are would be performed in a power system by evaluating the derived voltage stability index. Approach: Voltage Stability Index Lmn can be useful for estimating the distance from the current operating point to voltage collapse point. The index can either reveal the critical bus of a power system or the stability of each line connected between two buses in an interconnected network or evaluate the voltage stability margins of a system. Results: Flexible Alternating Current Transmission Systems (FACTS devices have been proposed as an effective solution for controlling power flow and regulating bus voltage in electrical power systems, resulting in an increased transfer capability, low system losses and improved stability. However to what extent the performance of FACTS devices can be brought out highly depends upon the location and the parameters of these devices. Unified Power Flow Controller (UPFC is the most promising FACTS device for power flow control. Conclusion/Recommendations: The performance of this index is presented and the effectiveness of the analyzed methods is demonstrated through simulation studies in IEEE 14 bus reliability test systems.
Stability of the classical type of relative equilibria of a rigid body in the J2 problem
Wang, Yue
2013-01-01
The motion of a point mass in the J2 problem is generalized to that of a rigid body in a J2 gravity field. The linear and nonlinear stability of the classical type of relative equilibria of the rigid body, which have been obtained in our previous paper, are studied in the framework of geometric mechanics with the second-order gravitational potential. Non-canonical Hamiltonian structure of the problem, i.e., Poisson tensor, Casimir functions and equations of motion, are obtained through a Poisson reduction process by means of the symmetry of the problem. The linear system matrix at the relative equilibria is given through the multiplication of the Poisson tensor and Hessian matrix of the variational Lagrangian. Based on the characteristic equation of the linear system matrix, the conditions of linear stability of the relative equilibria are obtained. The conditions of nonlinear stability of the relative equilibria are derived with the energy-Casimir method through the projected Hessian matrix of the variationa...
Institute of Scientific and Technical Information of China (English)
王发强; 李晶; 马西奎
2015-01-01
Positive output super-lift (POSL) Luo converter, which has some particular good features: such as its power switch being grounded, high voltage gain and positive polarity output, is a good topology for overcoming the drawbacks of the conventional Buck and Boost converters to obtain high output voltage and power for satisfying the requirements in practical engineering. In this paper, based on the averaging method and taking into account the abrupt changing of the voltage across the energy-transferring capacitor, the improved reduced order averaged model and the corresponding small signal model of the POSL Luo converter are established, and its transfer function from the duty cycle to the output voltage is derived and analyzed. By combining the derived transfer function from the duty cycle to the output voltage of the POSL Luo converter, with that for the voltage compensator and that for the pulse width modalation (PWM) generator, the transfer function from the reference voltage to the output voltage of the voltage-mode controlled POSL Luo converter is also derived. And then, the stability of the voltage-mode controlled POSL Luo converter is identified by calculating the poles of its transfer function from the reference voltage to the output voltage, so the corresponding stability boundaries are obtained. The power electronic simulator (PSIM) software is applied to simulate the POSL Luo converter in time domain and frequency domain to preliminarily confirm the effectiveness of the established transfer function from the duty cycle to the output voltage of the POSL Luo converter, and to simulate the voltage-mode controlled POSL Luo converter to preliminarily verify the theoretical analysis about its stability. Finally, the hardware circuits for the POSL Luo converter and the voltage-mode controlled POSL Luo converter are designed, and the circuit experimental results in time domain from the digital oscilloscope and in frequency domain from the impedance
Fish School Search Algorithm for Solving Optimal Reactive Power Dispatch Problem
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K. Lenin
2013-01-01
Full Text Available This paper presents an algorithm for solving the multi-objective reactive power dispatch problem in a power system. Modal analysis of the system is used for static voltage stability assessment. Loss minimization and maximization of voltage stability margin are taken as the objectives. Generator terminal voltages, reactive power generation of the capacitor banks and tap changing transformer setting are taken as the optimization variables. This paper presents fish school search a novel method of swarm intelligence for solving above problem. Fish school search Algorithm, which was inspired by the natural schooling behaviours of fish, a powerful stochastic optimization technique has been utilised to solve the reactive power optimization problem.
VOLTAGE REGULATORS OF SYNCHRONOUS GENERATORS
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Grigorash O. V.
2015-06-01
Full Text Available Synchronous generators are the primary source of electrical power autonomous electrosupply systems, including backup systems. They are also used in a structure of rotating electricity converters and are widely used in renewable energy as part of wind power plants of small, mini and micro hydroelectric plants. Increasing the speed and the accuracy of the system of the voltage regulation of synchronous generators is possible due to the development of combined systems containing more stabilizers. The article illustrates the functional schemes of circuit voltage stabilizers and frequency synchronous generators (with electromagnetic excitation and permanent magnet excitation and describes the features of their work, including two and three-aggregate rotating converters of electricity used in uninterruptible power supply systems. To improve the technical characteristics of the system of stabilization we have proposed functional solutions for stabilizers of synchronous generators made on the base of direct frequency converters and using a transformer with a rotating magnetic field. To improve the reliability of and to improve the operational characteristics of the autonomous independent sources of electricity we suggest creating the main functional blocks and the elements of the stabilization system in a modular way. The functional circuit solutions of voltage regulators of synchronous generators and the characteristics of their work considered in the article, are able to improve the efficiency of pre-design work in the development of new technical solutions for stabilizing the voltage and the frequency in synchronous generators of electrosupply autonomous systems
A stabilized explicit Lagrange multiplier based domain decomposition method for parabolic problems
Zheng, Zheming; Simeon, Bernd; Petzold, Linda
2008-05-01
A fully explicit, stabilized domain decomposition method for solving moderately stiff parabolic partial differential equations (PDEs) is presented. Writing the semi-discretized equations as a differential-algebraic equation (DAE) system where the interface continuity constraints between subdomains are enforced by Lagrange multipliers, the method uses the Runge-Kutta-Chebyshev projection scheme to integrate the DAE explicitly and to enforce the constraints by a projection. With mass lumping techniques and node-to-node matching grids, the method is fully explicit without solving any linear system. A stability analysis is presented to show the extended stability property of the method. The method is straightforward to implement and to parallelize. Numerical results demonstrate that it has excellent performance.
Stability Problem of Hyers-Ulam-Rassias for Generalized Forms of Cubic Functional Equation
Institute of Scientific and Technical Information of China (English)
Dong Seung KANG; Hahng-Yun CHU
2008-01-01
Let n≥2 be an integer number. In this paper, we investigate the generalized Hyers-Ulam- Rassias stability in Banach spaces and also Banach modules over a Banach algebra and a C*-algebra and the stability using the alternative fixed point of an n-dimensional cubic functional equation in Banach spaces:f (Σ 2n -1j=1xj + xn) + f( Σ 2n -1j=1xj -xn) +4n -1Σj=1f(xj)=16fΣn -1j=1xj +2n-1Σj=1(f(xj + xn)+f(xj -xn)) .
Application of HPEM to investigate the response and stability of nonlinear problems in vibration
DEFF Research Database (Denmark)
Mohammadi, M.H.; Mohammadi, A.; Kimiaeifar, A.;
2010-01-01
In this work, a powerful analytical method, called He's Parameter Expanding Methods (HPEM) is used to obtain the exact solution of nonlinear problems in nonlinear vibration. In this work, the governing equation is obtained by using Lagrange method, then the nonlinear governing equation is solved...... and convenient for solving these problems....
Hornman, Jorijn; de Winter, Andrea F; Kerstjens, Jorien M; Bos, Arend F; Reijneveld, Sijmen A
2017-08-01
To assess the stability of developmental problems in moderately-late preterm-born children compared with early preterm and full term-born children before school entry at age 4 years and 1 year after school entry at age 5 years. We included 376 early preterm, 688 born moderately-late preterm, and 403 full term-born children from the Longitudinal Preterm Outcome Project (LOLLIPOP) cohort study. Developmental problems were assessed by the total score and the 5 domain scores of the Ages and Stages Questionnaire at ages 4 (ASQ-4) and 5 (ASQ-5). From the combinations of normal and abnormal ASQ-4 and ASQ-5 scores we constructed 4 categories: consistently normal, emerging, resolving, and persistent problems. The ASQ-4 total score was abnormal more frequently in moderately-late preterm (7.9%, P = .016) and early preterm-born children (13.0%, P preterm-born children had persistence and change comparable with full term-born children, and early preterm-born children had significantly greater rates than full term-born children of persistent (8.4% vs 2.2%, P preterm and moderately-late preterm-born children had mainly emerging motor problems and resolving communication problems, but the changing rates of moderately-late preterm-born children were lower. After school entry, the overall development of moderately-late preterm-born children had stability patterns comparable with full term-born children, whereas early preterm-born children had greater rates of persistent and emerging problems. On the underlying domains, moderately-late preterm-born children had patterns comparable with early preterm-born children but at lower rates. Copyright © 2017 Elsevier Inc. All rights reserved.
SVG对双馈风电场电压稳定性的影响%Impact of SVG on the Voltage Stability of a DFIG-based Wind Farm
Institute of Scientific and Technical Information of China (English)
苏适; 严玉廷
2015-01-01
Recently, more and more accidents in wind farms show that the static var generators (SVGs) are effective reactive power compensation equipment which can prevent wind turbine tripping when fault occurs. The structure and working principle of SVG are introduced, and the control strategy of SVG is also presented. Through analysis of the impact of SVG on the voltage stability of an actual wind farm, an actual wind field model with SVG is constructed in the DIgSILENT / PowerFactory software. The simulation results show that the SVG can effectively improve the voltage stability of wind farms under different operation conditions.%近来,诸多风电场事故表明静止无功发生器(static var generator,SVG)是一种有效的无功补偿设备,可在故障期间防止风机脱网.介绍SVG的结构和工作原理,以及SVG的控制策略;然后通过分析SVG对实际风电场电压稳定性的影响,在DIgSILENT/PowerFactory软件中建立含SVG的实际风场模型.仿真结果表明SVG能有效地提高风电场在不同运行工况下的电压稳定.
METHOD OF COMPENSATING LOADS FOR SHALLOW SHELLS. VIBRATION AND STABILITY PROBLEMS
Tran Duc Chinh
2015-01-01
Based on the integral representation of the displacements functions through Green's functions, the author proposed a method to solve the system of differential equations of the given problem. The equations were solved approximately by reducing to algebraic equations by finite difference techniques in Samarsky scheme. Some examples are given for calculation of eigenvalues of shallow shell vibration problem, which are compared with results received by Onyashvili using Galerkin method.
METHOD OF COMPENSATING LOADS FOR SHALLOW SHELLS. VIBRATION AND STABILITY PROBLEMS
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Tran Duc Chinh
2015-12-01
Full Text Available Based on the integral representation of the displacements functions through Green's functions, the author proposed a method to solve the system of differential equations of the given problem. The equations were solved approximately by reducing to algebraic equations by finite difference techniques in Samarsky scheme. Some examples are given for calculation of eigenvalues of shallow shell vibration problem, which are compared with results received by Onyashvili using Galerkin method.
Influence of geometrical parameters on the linear stability of a Bénard-Marangoni problem
Hoyas, S.; Fajardo, P.; Pérez-Quiles, M. J.
2016-04-01
A linear stability analysis of a thin liquid film flowing over a plate is performed. The analysis is performed in an annular domain when momentum diffusivity and thermal diffusivity are comparable (relatively low Prandtl number, Pr =1.2 ). The influence of the aspect ratio (Γ ) and gravity, through the Bond number (Bo ), in the linear stability of the flow are analyzed together. Two different regions in the Γ -Bo plane have been identified. In the first one the basic state presents a linear regime (in which the temperature gradient does not change sign with r ). In the second one, the flow presents a nonlinear regime, also called return flow. A great diversity of bifurcations have been found just by changing the domain depth d . The results obtained in this work are in agreement with some reported experiments, and give a deeper insight into the effect of physical parameters on bifurcations.
Wheeler, A. A.; Mcfadden, G. B.; Murray, B. T.; Coriell, S. R.
1991-01-01
The effect of vertical, sinusoidal, time-dependent gravitational acceleration on the onset of solutal convection during directional solidification is analyzed in the limit of large modulation frequency. When the unmodulated state is unstable, the modulation amplitude required to stabilize the system is determined by the method of averaging. When the unmodulated state is stable, resonant modes of instability occur at large modulation amplitude. These are analyzed using matched asymptotic expansions to elucidate the boundary-layer structure for both the Rayleigh-Benard and directional solidification configurations. Based on these analyses, a thorough examination of the dependence of the stability criteria on the unmodulated Rayleigh number, Schmidt number, and distribution coefficient, is carried out.
Directory of Open Access Journals (Sweden)
M.A. Ali
2015-06-01
Full Text Available This study presents a new multi-objective approach for optimal placement of Static Compensator (STATCOM for global (overall voltage sag mitigation as well as for power system performance improvement. The problem is formulated as a non linear constrained multi-objective optimization problem and solved using Genetic Algorithm (GA. The proposed method determines optimal locations of STATCOMs which simultaneously minimizes the overall voltage sags at network buses, bus voltage deviation and system real power loss and maximizes the voltage stability margin of the system. The proposed approach has been applied on IEEE 24-bus Reliability Test System (RTS and IEEE 57-bus test systems. The details of implementation and simulation results are presented. The application results are promising and encouraging.
Energy Technology Data Exchange (ETDEWEB)
Ambrozy, G.
1986-01-01
The construction of large machinery that operates in opencast mines should by preceded by stability calculations as accurately as possible. The mathematical solution of the task is described. The method involves the determination of the coefficient matrix and of the coordinate functions. The accuracy of the results is estimated. Nomograms of the results obtained by using a computer program are presented. A numeric example verifies the validity of the mathematical solution.
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Nada S. Abdelwahab
2017-05-01
Full Text Available The present work concerns with the development of stability indicating the RP-HPLC method for simultaneous determination of guaifenesin (GUF and pseudoephedrine hydrochloride (PSH in the presence of guaifenesin related substance (Guaiacol. GUC, and in the presence of syrup excepients with minimum sample pre-treatment. In the developed RP-HPLC method efficient chromatographic separation was achieved for GUF, PSH, GUC and syrup excepients using ODS column as a stationary phase and methanol: water (50:50, v/v, pH = 4 with orthophosphoric acid as a mobile phase with a flow rate of 1 mL min−1 and UV detection at 210 nm. The chromatographic run time was approximately 10 min. Calibration curves were drawn relating the integrated area under peak to the corresponding concentrations of PSH, GUF and GUC in the range of 1–8, 1–20, 0.4–8 μg mL−1, respectively. The developed method has been validated and met the requirements delineated by ICH guidelines with respect to linearity, accuracy, precision, specificity and robustness. The validated method was successfully applied for determination of the studied drugs in triaminic chest congestion® syrup; moreover its results were statistically compared with those obtained by the official method and no significant difference was found between them.
Liang, X B; Si, J
2001-01-01
This paper investigates the existence, uniqueness, and global exponential stability (GES) of the equilibrium point for a large class of neural networks with globally Lipschitz continuous activations including the widely used sigmoidal activations and the piecewise linear activations. The provided sufficient condition for GES is mild and some conditions easily examined in practice are also presented. The GES of neural networks in the case of locally Lipschitz continuous activations is also obtained under an appropriate condition. The analysis results given in the paper extend substantially the existing relevant stability results in the literature, and therefore expand significantly the application range of neural networks in solving optimization problems. As a demonstration, we apply the obtained analysis results to the design of a recurrent neural network (RNN) for solving the linear variational inequality problem (VIP) defined on any nonempty and closed box set, which includes the box constrained quadratic programming and the linear complementarity problem as the special cases. It can be inferred that the linear VIP has a unique solution for the class of Lyapunov diagonally stable matrices, and that the synthesized RNN is globally exponentially convergent to the unique solution. Some illustrative simulation examples are also given.
Institute of Scientific and Technical Information of China (English)
李哓哓; 梁小栋
2015-01-01
异步风电场接入系统后会影响系统的暂态电压稳定性。采用电力系统仿真软件DIgSILENT/Power Factory设计出一种应用于恒速异步风电机组的静止无功补偿器（SVC）模型，并通过对风力发电机并入配电网的系统进行仿真计算来验证所建SVC模型对提高系统暂态稳定性的效果。仿真结果表明，在风速变化的情况下，SVC能够有效缓解恒速异步风电机组机端电压的波动；采用SVC设备能够有效改善异步风电场的电压稳定性，确保电网的安全稳定和风电机组的不间断运行。%ABSTRACT:Introducing the asynchronous wind farm into the electric power system will affect the transient voltage stability of the system.This paper designs a static var compensator (SVC)model used in a constant-speed asynchronous wind turbine by adopting the software of DIgSILENT/Power Factory, and verifies the effect of the SVC model for improving the transient stability of the system through the simulating calculation of the system incorporating the wind turbines into the distribution network, and based on the simulation results, points out that in the case of the wind-speed changing SVC can effectively relieve the terminal voltage of constant-speed asynchronous wind turbines, and adopting SVC equipment can effectively improve the voltage stability of the asynchronous wind farm, ensuring the the safety and stability of the grid and the continuous operation of the wind turbines.
Accurate Switched-Voltage voltage averaging circuit
金光, 一幸; 松本, 寛樹
2006-01-01
Abstract ###This paper proposes an accurate Switched-Voltage (SV) voltage averaging circuit. It is presented ###to compensated for NMOS missmatch error at MOS differential type voltage averaging circuit. ###The proposed circuit consists of a voltage averaging and a SV sample/hold (S/H) circuit. It can ###operate using nonoverlapping three phase clocks. Performance of this circuit is verified by PSpice ###simulations.
Institute of Scientific and Technical Information of China (English)
李江; 赵海岭; 常喜强; 宋联庆
2012-01-01
利用线路故障临界切除时间来表征电力系统暂态电压稳定性的量化指标,采取动态时域仿真法对WSCC3机9节点算例系统与基于直驱机组并网风电场接入该算例系统的暂态电压特性进行了仿真分析,研究结果表明,接入直驱机组风电场后算例系统的线路故障临界切除时间要比原算例系统的线路故障临界切除时间要长,因此,基于直驱机组风电场的接入算例系统能较好地改善原系统的暂态电压稳定性.%The transient voltage stabilities of a three—synchronous—generator and nine—bus power grid integrated with or without Direct-driven Permanent Magnet Synchronous Generator (D-PMSG) are simulated by dynamic time-domain method and compared by taking the fault critical clearing time as the quantitative indicator of transient voltage stability of power system. The results show that the fault critical clearing time of grid integrated with D-PMSG is longer than the grid without D-PMSG, and so the integration of D—PMSG into grid can improve the stability of grid.
Stability Estimates for h-p Spectral Element Methods for Elliptic Problems
Dutt, Pravir; Tomar, Satyendra; Kumar, B.V. Rathish
2002-01-01
In a series of papers of which this is the first we study how to solve elliptic problems on polygonal domains using spectral methods on parallel computers. To overcome the singularities that arise in a neighborhood of the corners we use a geometrical mesh. With this mesh we seek a solution which min
Stability Estimates for h-p Spectral Element Methods for Elliptic Problems
Dutt, Pravir; Tomar, S.K.; Kumar, B.V. Rathish
2002-01-01
In a series of papers of which this is the first we study how to solve elliptic problems on polygonal domains using spectral methods on parallel computers. To overcome the singularities that arise in a neighborhood of the corners we use a geometrical mesh. With this mesh we seek a solution which
Institute of Scientific and Technical Information of China (English)
赵海涛; 刘丽华; 吴凯; 张建国; 方广有
2013-01-01
Transient electromagnetic transmitter is an important part in transient electromagnetic detection equipment. In the aspects of high-power current steep pulse transmission, high precision synchronous control, falling-edge linearity , short turn-off time, turn-off time measurement and etc. , there are still a lot of problems to be solved urgently. This paper proposes a novel extra fast turn-off transient electromagnetic transmitting system, DSP and FPGA are used to work together and provide the system with reliable driving signals and protective measures. The system adopts a voltage stabilized clamping circuit and a damping resistance circuit, and has the characteristics of short turn-off time, high current falling-edge linearity and high transmission current; besides it can improve the speed of pulse current rising-edge. The system also adopts a novel turn-off time measurement circuit, which makes the measurement simple and accurate. A GPS synchronous controller is designed, which adopts a cooperative operation mode with a temperature compensated crystal, solves the GPS short-time failure problem and improves the reliability of the system. The transmitting system field experiment was carried out,experiment results show that the system features high transmission current, good current falling-edge linearity, accurate turn-off time measurement, and precise and reliable synchronous control. The system is easy to carry,convenient to operate,and has excellent performance.%瞬变电磁发射机是瞬变电磁探测设备中的重要组成部分,在大功率电流陡脉冲发射、高精度同步控制、下降沿线性度、短关断时间和关断时间测量等方面,有许多亟待解决的问题.提出了一种瞬变电磁发射系统,DSP和FPGA协同工作为系统提供可靠的驱动信号和保护措施；提出了恒压钳位电路,配合合适的阻尼吸收电路,具有关断时间短、电流下降沿线性度高和发射电流大的特点,并可提升脉冲
Power-Voltage Characteristics of Power System with the Long Transmission Line
Directory of Open Access Journals (Sweden)
Prechanon Kumkratug
2012-01-01
Full Text Available Problem statement: Power- Voltage curve provides very important information for voltage stability analysis. The exact long transmission line model consists of the resistance and the reactance. The resistance causes in the active line loss. It is not easy task to achieve the power-voltage curve characteristics of power system with the exact long line model. Approach: This study applies the concept of the Newton-Raphson method to iteratively solve the nonlinear power flow equations. The Power-Voltage (P-V curve characteristic of the system without line loss and with line loss are plotted and compared on various cases. Results: It is found from the study that the resistance of the line obviously provides the negative effects on the voltage stability. The line loss causes in the decrement of the critical point. In addition, it is found that the leading power factor can increase the critical point of P-V curve. Conclusion: The exact long line model should be considered for voltage stability analysis of the system with the long transmission line.
Energy Technology Data Exchange (ETDEWEB)
Kevin L. Gering; Mason K. Harrup; Eric J. Dufek; Sergiy V. Sazhin; Harry W. Rollins; David K. Jamison; Fred F. Stewart; John Burba
2013-09-01
Electrolytes play a central role in performance and aging in most electrochemical systems. As automotive and grid applications place a higher reliance on electrochemical stored energy, it becomes more urgent to have electrolyte components that enable optimal battery performance while promoting battery safety and longevity. Safety remains a foremost concern for widespread utilization of Li-ion technology in electric-drive vehicles, especially as the focus turns to higher voltage systems (5V). This work capitalizes on the long established INL expertise regarding phosphazene chemistry, aimed at battery-viable compounds for electrolytes and electrodes that are highly tolerant to abusive conditions. This report showcases our 2013 work for the DOE applied battery research (ABR) program, wherein testing results are summarized for INL electrolytes and alternative anode materials.
Mode decomposition of nonlinear eigenvalue problems and application in flow stability
Institute of Scientific and Technical Information of China (English)
高军; 罗纪生
2014-01-01
Direct numerical simulations are carried out with different disturbance forms introduced into the inlet of a flat plate boundary layer with the Mach number 4.5. According to the biorthogonal eigenfunction system of the linearized Navier-Stokes equations and the adjoint equations, the decomposition of the direct numerical simulation results into the discrete normal mode is easily realized. The decomposition coefficients can be solved by doing the inner product between the numerical results and the eigenfunctions of the adjoint equations. For the quadratic polynomial eigenvalue problem, the inner product operator is given in a simple form, and it is extended to an N th-degree polynomial eigenvalue problem. The examples illustrate that the simplified mode decomposition is available to analyze direct numerical simulation results.
On the stability of the Travelling Salesman Problem algorithm of Hopfield and Tank.
Wilson, G V; Pawley, G S
1988-01-01
The application of the method of Hopfield and Tank to the Travelling Salesman Problem (1985) has been re-examined in an effort to find a procedure for scaling to system sizes of real interest. As this failed, methods were tried to improve the algorithm, recognizing the importance of a "silicon implementation". No satisfactory refinement was found, and the reasons for algorithm failure have been identified.
Stability of pseudospectral and finite-difference methods for variable coefficient problems
Gottlieb, D.; Orszag, S. A.; Turkel, E.
1981-01-01
It is shown that pseudospectral approximation to a special class of variable coefficient one-dimensional wave equations is stable and convergent even though the wave speed changes sign within the domain. Computer experiments indicate similar results are valid for more general problems. Similarly, computer results indicate that the leapfrog finite-difference scheme is stable even though the wave speed changes sign within the domain. However, both schemes can be asymptotically unstable in time when a fixed spatial mesh is used.
Garcia-Perciante, A L; Brun-Battistini, D; Sandoval-Villalbazo, A
2014-01-01
Extended theories are widely used in the literature to describe relativistic fluids. The motivation for this is mostly due to the causality issues allegedly present in the first order in the gradients theories. However, the decay of fluctuations in the system is also at stake when first order theories that couple heat with acceleration are used. This paper shows that although the introduction of the Maxwell-Cattaneo equation in the description of a simple relativistic fluid formally eliminates the generic instabilities identified by Hiscock and Lindblom in 1985, the hypothesis on the order of magnitude of the corresponding relaxation term contradicts the basic ordering in Knudsen's parameter present in the kinetic approach to hydrodynamics. It is shown that the time derivative, stabilizing term is of second order in such parameter and thus does not belong to the Navier-Stokes regime where the so-called instability arises.
Nair, Nirmal-Kumar
As open access market principles are applied to power systems, significant changes are happening in their planning, operation and control. In the emerging marketplace, systems are operating under higher loading conditions as markets focus greater attention to operating costs than stability and security margins. Since operating stability is a basic requirement for any power system, there is need for newer tools to ensure stability and security margins being strictly enforced in the competitive marketplace. This dissertation investigates issues associated with incorporating voltage security into the unbundled operating environment of electricity markets. It includes addressing voltage security in the monitoring, operational and planning horizons of restructured power system. This dissertation presents a new decomposition procedure to estimate voltage security usage by transactions. The procedure follows physical law and uses an index that can be monitored knowing the state of the system. The expression derived is based on composite market coordination models that have both PoolCo and OpCo transactions, in a shared stressed transmission grid. Our procedure is able to equitably distinguish the impacts of individual transactions on voltage stability, at load buses, in a simple and fast manner. This dissertation formulates a new voltage stability constrained optimal power flow (VSCOPF) using a simple voltage security index. In modern planning, composite power system reliability analysis that encompasses both adequacy and security issues is being developed. We have illustrated the applicability of our VSCOPF into composite reliability analysis. This dissertation also delves into the various applications of voltage security index. Increasingly, FACT devices are being used in restructured markets to mitigate a variety of operational problems. Their control effects on voltage security would be demonstrated using our VSCOPF procedure. Further, this dissertation investigates
Prounikov, Igor
2012-01-01
Stationary differential systems with polynomial right sides are considered. Necessary and sufficient conditions are formulated when a given domain is a domain of asymptotic stability and the origin of coordinates is either focus or center. The problem of construction of a stabilizing control in the form of polynomial is studied.
Luo, Tao; Xin, Zhouping; Zeng, Huihui
2016-11-01
The nonlinear asymptotic stability of Lane-Emden solutions is proved in this paper for spherically symmetric motions of viscous gaseous stars with the density dependent shear and bulk viscosities which vanish at the vacuum, when the adiabatic exponent {γ} lies in the stability regime {(4/3, 2)}, by establishing the global-in-time regularity uniformly up to the vacuum boundary for the vacuum free boundary problem of the compressible Navier-Stokes-Poisson systems with spherical symmetry, which ensures the global existence of strong solutions capturing the precise physical behavior that the sound speed is {C^{{1}/{2}}}-Hölder continuous across the vacuum boundary, the large time asymptotic uniform convergence of the evolving vacuum boundary, density and velocity to those of Lane-Emden solutions with detailed convergence rates, and the detailed large time behavior of solutions near the vacuum boundary. Those uniform convergence are of fundamental importance in the study of vacuum free boundary problems which are missing in the previous results for global weak solutions. Moreover, the results obtained in this paper apply to much broader cases of viscosities than those in Fang and Zhang (Arch Ration Mech Anal 191:195-243, 2009) for the theory of weak solutions when the adiabatic exponent {γ} lies in the most physically relevant range. Finally, this paper extends the previous local-in-time theory for strong solutions to a global-in-time one.
Institute of Scientific and Technical Information of China (English)
张谦; 廖清芬; 唐飞; 徐君茹; 刘涤尘; 邹宏亮
2015-01-01
In order to study the impact of inter-connection of distributed generators (DGs) on steady state voltage stability of distribution network,the voltage stability index(VSI) capable of reflecting the degree of voltage stability of all load buses in distribution network is derived.A new load increase strategy for distribution network is proposed to quantitatively analyze the voltage stability of the weakest bus and the whole system.Causes of distribution network voltage collapse are discussed using PV curves,and the effects on steady state voltage stability in centralized and distributed inter-connection mode are compared when DG output varies dramatically.Furthermore,a voltage stability analysis method based on the calculation of VSI value of all buses is proposed to rapidly rank the voltage stability margin of load buses as well as accurately locate the weakest bus. Simulation results prove that rational location of DG inter-connection is expected to improve voltage stability of the entire network.%为研究分布式电源(DG)接入对配电网静态电压稳定的影响问题，推导了能反映配电网各负荷节点电压稳定程度的电压稳定指标，提出了一种针对配电网的负荷增长策略，对 DG 接入前后全网最薄弱节点以及整个系统的静态电压稳定性进行了定量分析，结合 PV 曲线探讨了配电网电压崩溃事故的发生机理，对比分析了 DG 出力波动性较大时，集中接入和分散接入方式对静态电压稳定性的改善效果。所提的基于系统各节点电压稳定指标计算的静态电压稳定性分析方法可对负荷节点电压稳定裕度进行快速排序，并可实现全网薄弱节点的准确定位。DG 接入前后的仿真实验结果表明，合理位置的 DG 接入可有效改善全网的静态电压稳定性。
Zingan, Valentin Nikolaevich
This work develops a discontinuous Galerkin finite element discretization of non- linear hyperbolic conservation equations with efficient and robust high order stabilization built on an entropy-based artificial viscosity approximation. The solutions of equations are represented by elementwise polynomials of an arbitrary degree p > 0 which are continuous within each element but discontinuous on the boundaries. The discretization of equations in time is done by means of high order explicit Runge-Kutta methods identified with respective Butcher tableaux. To stabilize a numerical solution in the vicinity of shock waves and simultaneously preserve the smooth parts from smearing, we add some reasonable amount of artificial viscosity in accordance with the physical principle of entropy production in the interior of shock waves. The viscosity coefficient is proportional to the local size of the residual of an entropy equation and is bounded from above by the first-order artificial viscosity defined by a local wave speed. Since the residual of an entropy equation is supposed to be vanishingly small in smooth regions (of the order of the Local Truncation Error) and arbitrarily large in shocks, the entropy viscosity is almost zero everywhere except the shocks, where it reaches the first-order upper bound. One- and two-dimensional benchmark test cases are presented for nonlinear hyperbolic scalar conservation laws and the system of compressible Euler equations. These tests demonstrate the satisfactory stability properties of the method and optimal convergence rates as well. All numerical solutions to the test problems agree well with the reference solutions found in the literature. We conclude that the new method developed in the present work is a valuable alternative to currently existing techniques of viscous stabilization.
Han, Zhong-Jie; Xu, Gen-Qi
2015-08-01
In this paper, a transmission problem between elastic and thermoelastic material is considered. Assume that these two materials are connected by a vibrating concentrated mass. By a detailed spectral analysis, the asymptotic expressions of the eigenvalues of the system are obtained, and based on which, the Riesz basis property of the eigenvectors is deduced. It is proved that the total energy of this system cannot achieve exponential decay. However, by the frequency domain method together with some multiplier techniques, the polynomial decay of the system is showed and the optimal decay rate is estimated. Finally, some numerical simulations are given to support the results obtained in this paper.
Application of HPEM to investigate the response and stability of nonlinear problems in vibration
DEFF Research Database (Denmark)
Mohammadi, M.H.; Mohammadi, A.; Kimiaeifar, A.
2010-01-01
In this work, a powerful analytical method, called He's Parameter Expanding Methods (HPEM) is used to obtain the exact solution of nonlinear problems in nonlinear vibration. In this work, the governing equation is obtained by using Lagrange method, then the nonlinear governing equation is solved...... analytically by He's Parameter Expanding Methods. It is shown that one term in series expansions is sufficient to obtain a highly accurate solution which is valid for the whole domain. Comparison of the obtained solutions with those obtained using numerical method shows that this method is effective...
Energy Technology Data Exchange (ETDEWEB)
Cortez, Anderson Neves [Companhia Energetica de Minas Gerais (CEMIG), Belo Horizonte, MG (Brazil)]. E-mail: anderson@cemig.com.br
2001-07-01
This article presents an alternative methodology of voltage stability determination of Electrical Power System (EPS), focusing technical and economical aspects. In this direction, it presents relative aspects to mathematical modelling to analyse the phenomenon and also the influence from the most important dynamics to be taken into consideration. It is inquired the participation of generators in the rearrangement of the adopted active power in the current criteria of margin determination. A real system is analyzed, under this aspect, indicating significant variations in the calculated values for the margins, resulting in improper investments of significant values. The proposed methodology by this article seeks to contribute to minimize such mistakes, this is done by means of focusing the long duration dynamics of generators, what constitutes an important progress in relation to the researches about them.
Hierarchy problem, gauge coupling unification at the Planck scale, and vacuum stability
Directory of Open Access Journals (Sweden)
Naoyuki Haba
2015-11-01
Full Text Available From the point of view of the gauge hierarchy problem, introducing an intermediate scale in addition to TeV scale and the Planck scale (MPl=2.4×1018 GeV is unfavorable. In that way, a gauge coupling unification (GCU is expected to be realized at MPl. We explore possibilities of GCU at MPl by adding a few extra particles with TeV scale mass into the standard model (SM. When extra particles are fermions and scalars (only fermions with the same mass, the GCU at MPl can (not be realized. On the other hand, when extra fermions have different masses, the GCU can be realized around 8πMPl without extra scalars. This simple SM extension has two advantages that a vacuum becomes stable up to MPl (8πMPl and a proton lifetime becomes much longer than an experimental bound.
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
[1]Oleinik, O. A., Samokhin,V. N., Mathematical Models in Boundary Layer Theorem, Boca Raton; Chapman and Hall/CRC, 1999.[2]Volpert, A.I., Hudjaev, S.I., On the problem for quasilinear degenerate parabolic equations of second order(Russian), Mat. Sb., 1967, 3: 374-396.[3]Zhao, J., Uniqueness of solutions of quasilinear degenerate parabolic equations, Northeastern Math. J., 1985,1(2): 153-165.[4]Wu, Z., Yin, J., Some properties of functions in BVx and their applications to the uniqueness of solutions for degenerate quasilinear parabolic equations, Northeastern Math. J., 1989,5(4): 395-422.[5]Brezis, H., Crandall, M.G., Uniqueness of solutions of the initial value problem for ut- △ψ(u) = 0, J.Math. Pures et Appl., 1979, 58: 153-163.[6]Kruzkov, S.N., First order quasilinear equations in several independent varaiables, Math. USSR-Sb., 1970, 10:217-243.[7]Cockburn, B., Gripenberg, G., Continious dependence on the nonlinearities of solutions of degenerate parabolic equations, J. Diff. Equatiaons, 1999, 151: 231-251.[8]Volpert, A.I., BV space and quasilinear equations, Mat. Sb., 1967, 73: 255-302.[9]Volpert, A.I., Hudjave, S.I., Analysis of class of discontinuous functions and the equations of mathematical physics (Russian), Izda. Nauka Moskwa, 1975.[10]Evans, L.C., Weak convergence methods for nonlinear partial differential equations, Conference Board of the Mathematical Sciences, Regional Conferences Series in Mathematics Number 74, 1998.[11]Wu, Z., Zhao, J., Yin, J., et al., Nonlinear Diffusion Equations, Singapore: Word Scientific, 2001.
Murmann, Patrick; Streipert, Benjamin; Kloepsch, Richard; Ignatiev, Nikolai; Sartori, Peter; Winter, Martin; Cekic-Laskovic, Isidora
2015-04-14
Lithium-cyclo-difluoromethane-1,1-bis(sulfonyl)imide (LiDMSI) was evaluated as an electrolyte additive in lithium-ion batteries for improved high voltage applications. Cycling the cathode at high potentials leads to the electrochemical oxidation of the salt to form a cathode electrolyte interphase (CEI) layer on the cathode surface. With the addition of 2 wt% of LiDMSI to the 1 M LiPF6 in 1 : 1 (by wt) EC : DEC electrolyte, the capacity retention and the Coulombic efficiency in LiNi1/3Co1/3Mn1/3O2/Li-half-cells as well as in LiNi1/3Co1/3Mn1/3O2/graphite-full-cells were improved. The cycling results point out the less over-potential and resistance at the cathode/electrolyte interface. These improvements are studied by SEM, EIS and XPS techniques.
Directory of Open Access Journals (Sweden)
Yekini Shehu
2010-01-01
real Banach space which is also uniformly smooth using the properties of generalized f-projection operator. Using this result, we discuss strong convergence theorem concerning general H-monotone mappings and system of generalized mixed equilibrium problems in Banach spaces. Our results extend many known recent results in the literature.
The Problem of Matter Stability in the Nambu-Jona-Lasinio Model
Buballa, M
1996-01-01
We reinvestigate the conditions for stable matter solutions in the Nambu--Jona-Lasinio (NJL) model. In mean field approximation the NJL model can be regarded as an extension of the Walecka mean field model to include negative energy fermion states. While this extension is necessary to allow for a chiral phase transition, it was found some time ago that at the same time it destroys the wanted saturation properties of the Walecka model. We reformulate this problem in terms of the thermodynamic potential and find that there is indeed a connection between these two features. We show that the minimum of the thermodynamic potential which corresponds to stable nuclear matter in the Walecka model is shifted from a finite to zero effective fermion mass in the chiral NJL model. This shift is closely related to the chiral phase transition. Under certain conditions the shifted minima may still lead to stable matter solutions but only in the chirally restored phase. We discuss a possible interpretation of these solutions ...
Stability of the Moons orbits in Solar system in the restricted three-body problem
Ershkov, Sergey V
2015-01-01
We consider the equations of motion of three-body problem in a Lagrange form (which means a consideration of relative motions of 3-bodies in regard to each other). Analyzing such a system of equations, we consider in details the case of moon motion of negligible mass m3 around the 2-nd of two giant-bodies m1, m2 (which are rotating around their common centre of masses on Kepler trajectories), the mass of which is assumed to be less than the mass of central body. Under assumptions of R3BP, we obtain the equations of motion which describe the relative mutual motion of the centre of mass of 2-nd giant-body m2 (Planet) and the centre of mass of 3-rd body (Moon) with additional effective mass placed in that centre of mass. They should be rotating around their common centre of masses on Kepler elliptic orbits. For negligible effective mass it gives the equations of motion which should describe a quasi-elliptic orbit of 3-rd body (Moon) around the 2-nd body m2 (Planet) for most of the moons of the Planets in Solar s...
Hierarchy problem, gauge coupling unification at the Planck scale, and vaccum stability
Haba, Naoyuki; Takahashi, Ryo; Yamaguchi, Yuya
2014-01-01
Regarding to the gauge hierarchy problem, an intermediate scale, such as a grand unification scale of ${\\cal O}(10^{16})\\,{\\rm GeV}$, is disfavored, and allowed mass scale is only TeV scale. For this motivation, we explore possibilities of gauge coupling unification (GCU) at the Planck scale ($M_{Pl} = 2.4 \\times 10^{18}\\,{\\rm GeV}$) by adding a few extra particles with TeV scale mass into the standard model. We find that, when all extra particles have the same mass, the GCU at the Planck scale cannot be realized only by extra fermions, but can be done by extra particles including some scalars. On the other hand, when extra fermions have different masses, the GCU can be realized around $\\sqrt{8 \\pi} M_{Pl}$ only by themselves. By this extension, a vacuum becomes stable up to the Planck scale as well as a proton lifetime is much longer than an experimental lower bound.
Schröder, Jörg; Viebahn, Nils; Wriggers, Peter; Auricchio, Ferdinando; Steeger, Karl
2017-05-01
In this work we investigate different mixed finite element formulations for the detection of critical loads for the possible occurrence of bifurcation and limit points. In detail, three- and two-field formulations for incompressible and quasi-incompressible materials are analyzed. In order to apply various penalty functions for the volume dilatation in displacement/pressure mixed elements we propose a new consistent scheme capturing the non linearities of the penalty constraints. It is shown that for all mixed formulations, which can be reduced to a generalized displacement scheme, a straight forward stability analysis is possible. However, problems based on the classical saddle-point structure require a different analyses based on the change of the signature of the underlying matrix system. The basis of these investigations is the work from Auricchio et al. (Comput Methods Appl Mech Eng 194:1075-1092, 2005, Comput Mech 52:1153-1167, 2013).
DEFF Research Database (Denmark)
Martin, Marie H. T.; D. Nielsen, Maj Britt; Pedersen, Jacob
2015-01-01
PURPOSE: Mental health problems (MHPs) are increasingly common as reasons for long-term sickness absence. However, the knowledge of how to promote a stable return to work (RTW) after sickness absence due to MHPs is limited. The purpose of this study was to assess the effects of a multidisciplinary......) and of conventional case management (n = 80) for 2 years to compare their risk of recurrent sickness absence and unemployment after RTW, their cumulative sickness absence and their labour market status after 2 years. RESULTS: We found no statistically significant intervention effect in terms of the risk of recurrent...... showed no benefits in terms of improved stability of RTW, reduced sickness absence or improved labour market status after 2 years when compared to conventional case management. IMPLICATIONS FOR REHABILITATION: Evidence for effective return-to-work (RTW) interventions for people with mental health...
Energy Technology Data Exchange (ETDEWEB)
Tare, U.A. [Haliburton, Calgary, AB (Canada); Mody, F.K. [Shell International E and P Inc., Calgary, AB (Canada); Tan, C.P. [CSIRO Petroleum, Kensington, WA (Australia)
2002-06-01
Drilling and completion operations in shales often suffer as a result of wellbore instability. Mechanical failure of the rock around a wellbore is the primary cause of shale instability. This process can be exacerbated by physico-chemical interactions between drilling fluids and shales. Water-based drilling fluids are used more and more due to environmental awareness that becomes more prevalent. Wellbore instability problems can however result from an improper application of water-based drilling fluids in those cases where drilling occurs in sensitive clay-rich formations. To meet the requirements of the petroleum industry, considerable collaborative efforts were expanded in the development of innovative environmentally acceptable water-based drilling fluids. In this paper, the authors describe the process that leads to the development of these drilling fluids. It is possible to achieve shale stability through an osmotic outflow of pore fluid and prevention/minimization of mud pressure penetration, as laboratory experiments on shale samples under realistic downhole conditions exposed to these drilling fluids prove. High membrane efficiencies, in excess of 80 per cent, were generated by this new generation of membrane efficient water-based drilling fluids. Drilling objectives resulting from an improved application of water-based drilling fluids are made possible by a fundamental understanding of the main drilling fluid-shale interaction mechanisms for shale stability and the application of experimental data to field conditions. The authors indicate that the achievement of trouble-free drilling of shales and notable reductions in non-productive time is accomplished by following the practical guidelines included in this paper for maintaining shale stability with the new generation of water-based drilling fluids. 8 refs., 2 tabs., 4 figs.
A battery-based, low-noise voltage source
Wagner, Anke; Sturm, Sven; Schabinger, Birgit; Blaum, Klaus; Quint, Wolfgang
2010-06-01
A highly stable, low-noise voltage source was designed to improve the stability of the electrode bias voltages of a Penning trap. To avoid excess noise and ground loops, the voltage source is completely independent of the public electric network and uses a 12 V car battery to generate output voltages of ±15 and ±5 V. First, the dc supply voltage is converted into ac-voltage and gets amplified. Afterwards, the signal is rectified, filtered, and regulated to the desired output value. Each channel can deliver up to 1.5 A. The current as well as the battery voltage and the output voltages can be read out via a universal serial bus (USB) connection for monitoring purposes. With the presented design, a relative voltage stability of 7×10-7 over 6.5 h and a noise level equal or smaller than 30 nV/√Hz is achieved.
Indian Academy of Sciences (India)
Jagadish Singh; Joel John Taura
2014-06-01
We have examined the effects of oblateness up to 4 of the less massive primary and gravitational potential from a circum-binary belt on the linear stability of triangular equilibrium points in the circular restricted three-body problem, when the more massive primary emits electromagnetic radiation impinging on the other bodies of the system. Using analytical and numerical methods, we have found the triangular equilibrium points and examined their linear stability. The triangular equilibrium points move towards the line joining the primaries in the presence of any of these perturbations, except in the presence of oblateness up to 4 where the points move away from the line joining the primaries. It is observed that the triangular points are stable for 0 < < c and unstable for c ≤ ≤ $\\frac{1}{2}$, where c is the critical mass ratio affected by the oblateness up to 4 of the less massive primary, electromagnetic radiation of the more massive primary and potential from the belt, all of which have destabilizing tendencies, except the coefficient 4 and the potential from the belt. A practical application of this model could be the study of motion of a dust particle near a radiating star and an oblate body surrounded by a belt.
A Simple Analytical Approach to the Aeroelastic Stability Problem of Long-Span Cable-Stayed Bridges
Vairo, Giuseppe
2010-01-01
This paper deals with the aeroelastic stability problem of long-span cable-stayed bridges under an approaching crosswind flow. Starting from a continuous model of the fan-shaped bridge scheme with both H- or A-shaped towers, critical states of the coupled wind-structure system are identified by means of a variational formulation, accounting for torsional and flexural (vertical and lateral) bridge oscillations. The overall bridge dynamics is described by introducing simple mechanical systems with equivalent stiffness properties and, under the assumption of a prevailing truss-like bridge behavior, analytical estimates for dominant stiffness contributions are proposed. Several case studies are discussed and comparisons with experimental evidences as well as with available analytical and numerical results are presented. The proposed simplified approach proves to be consistent and effective for successfully capturing the main wind-bridge interaction mechanisms, and it could be considered as a useful engineering tool for the aeroelastic stability analysis of long-span cable-stayed bridges.
Narayan, A.; Usha, T.
2014-05-01
This paper studies the stability of infinitesimal motions about the triangular equilibrium points in the elliptic restricted three body problem assuming bigger primary as a source of radiation and the smaller one a triaxial rigid body. The perturbation technique developed by Bennet (Icarus 4:177, 1965b) has been used for determination of characteristic exponents. This technique is based on Floquet's Theory for determination of characteristic exponents in the system with periodic coefficients. The results of the study are analytical and numerical expressions are simulated for the transition curves bounding the region of stability in the μ-e plane, accurate to O( e 2). The unstable region is found to be divided into three parts. The effect of radiation parameter is significant. For small values of e, the results are in favor with the numerical analysis of Danby (Astron. J. 69:166, 1964), Bennet (Icarus 4:177, 1965b), Alfriend and Rand (AIAA J. 6:1024, 1969). The effect of radiation pressure is significant than the oblateness and triaxiality of the primaries.
Development of a voltage scanner of chopper
Shen Guan Ren; LiShengLi; WangQuanXing; Wu Long Cheng
2001-01-01
Development of voltage sweeper of chopper with CPNG are introduced. Voltage sweeper is one of important key parts of chopper. Two years working prove that it is stable and reliable. Its main technology performance save: sine wave frequency: 750 kHz +- 20 Hz; total distortion: 65 Db; output voltage (V-V): 0->=4000 V; the error7 W; voltage supply: 220V AC +-10%, 50 +- 1 Hz; total power supply: <100W; Work temperature range: 0 - 40 degree; Stability in long time <=1%
Yi, Ting-Feng; Mei, Jie; Zhu, Yan-Rong
2016-06-01
Spinel LiNi0.5Mn1.5O4 (LNMO) is one of the most promising high voltage cathode materials for future application due to its advantages of large reversible capacity, high thermal stability, low cost, environmental friendliness, and high energy density. LNMO can provide 20% and 30% higher energy density than traditional cathode materials LiCoO2 and LiFePO4, respectively. Unfortunately, LNMO-based batteries with LiPF6-based carbonate electrolytes always suffer from severe capacity deterioration and poor thermostability because of the oxidization of organic carbonate solvents and decomposition of LiPF6, especially at elevated temperatures and water-containing environment. Hence, it is necessary to systematically and comprehensively summarize the progress in understanding and modifying LNMO cathode from various aspects. In this review, the structure, transport properties and different reported possible fading mechanisms of LNMO cathode are first discussed detailedly. And then, the major goal of this review is to highlight new progress in using proposed strategies to improve the cycling stability and rate capacity of LNMO-based batteries, including synthesis, control of special morphologies, element doping and surface coating etc., especially at elevated temperatures. Finally, an insight into the future research and further development of LNMO cathode is discussed.
Calamba, K. M.; Schramm, I. C.; Johansson Jõesaar, M. P.; Ghanbaja, J.; Pierson, J. F.; Mücklich, F.; Odén, M.
2017-08-01
Aspects on the phase stability and mechanical properties of nitrogen deficient (Ti0.54Al0.46)Ny alloys were investigated. Solid solution alloys of (Ti,Al)N were grown by cathodic arc deposition. The kinetic energy of the impinging ions was altered by varying the substrate bias voltage from -30 V to -80 V. Films deposited with a high bias value of -80 V showed larger lattice parameter, finer columnar structure, and higher compressive residual stress resulting in higher hardness than films biased at -30 V when comparing their as-deposited states. At elevated temperatures, the presence of nitrogen vacancies and point defects (anti-sites and self-interstitials generated by the ion-bombardment during coating deposition) in (Ti0.54Al0.46)N0.87 influence the driving force for phase separation. Highly biased nitrogen deficient films have point defects with higher stability during annealing, which cause a delay of the release of the stored lattice strain energy and then accelerates the decomposition tendencies to thermodynamically stable c-TiN and w-AlN. Low biased nitrogen deficient films have retarded phase transformation to w-AlN, which results in the prolongment of age hardening effect up to 1100 °C, i.e., the highest reported temperature for Ti-Al-N material system. Our study points out the role of vacancies and point defects in engineering thin films with enhanced thermal stability and mechanical properties for high temperature hard coating applications.
Directory of Open Access Journals (Sweden)
ZaidGarcia Sánchez
2013-06-01
Full Text Available En este trabajo se presenta un análisis de la influencia de la naturaleza de la carga en la estabilidad de tensión. El margen de carga es un índice considerado exacto para el análisis de la estabilidad de la tensión, sin embargo tradicionalmente se ha asumido la carga para obtener este índice como carga de potencia constante, esto no refleja fielmente el comportamiento de la misma cuando se deterioran las condiciones de tensión en el sistema eléctrico. Se demuestra la influencia del factor de potencia de la carga en la obtención del punto de máxima carga del sistema, así como la influencia de la misma en la obtención del punto de estabilidad por tensión y el punto de máxima carga. Se implementó un programa para la determinación en tiempo real del margen de carga. La metodología fue probada con sistemas de prueba de la IEEE y con un sistema real.In this paper an analysis of the influence of the nature of the load is presented in the stability tension. The load margin is an exact indices to analyses voltage stability, however traditionally it has been considered the load for obtain these indices as a constant power load, this does not show faithfully the behavior of the load when the condition of tension in the electric system are deteriorate. It is demonstrated the influence of the load power factor in the obtaining of the maximum power load of the system, such as the influence of this one in the obtaining of the stability point and maximum load point. This paper presents software to obtain the load margin for on-line studies. The methodology was tested with IEEE test systems and a real system.
Directory of Open Access Journals (Sweden)
Zaid García Sánchez
2011-05-01
Full Text Available En Cuba desde la década del 70 se empezaron a desarrollar algoritmos para realizar el estudio de los regímenes estacionarios y transitorios del Sistema Eléctrico Nacional (SEN. Particular énfasis se hizo sobre el desarrollo de algoritmos y programas para computadoras para realizar el estudio de la estabilidad transitoria. Actualmente se utiliza ampliamente el programa Power System Explorer (PSX, el que posee amplias facilidades para realizar estudios sobre regímenes estaciones y transitorios de los sistemas eléctricos de potencia. A través de los estudios realizados para la planificación y la experiencia alcanzada sobre la explotación del SEN, con su estructura actual, se ha revelado la necesidad de estudiar en detalles los problemas relacionados con el voltaje, en particular el problema de la estabilidad del voltaje del SEN. En este artículo se realiza una primera revisión sobre algunos de los métodos matemáticos estáticos y dinámicos que se han desarrollado y que recoge la bibliografía sobre el tema de la Estabilidad del Voltaje en los Sistemas Eléctricos de Potencia. In Cuba, from the seventies of the past century, different algorithms to study stationary and transient regimes of the Cuban Electric System were developed. Those algorithms and computer programs were focused in the study of transient stability. Currently, we use widely the computer program “Power System Explorer” (PSX which have a lot of facilities to make studies about stationary and transient regimes of electric power systems. Due to the studies about planning of electric power systems and the accumulated experience working with Cuban Electric System, the need of study the problems related with voltage stability of Cuban Electric System has arisen. In this paper, we make a first review about some static and dynamic mathematical methods included in bibliography about voltage stability of electric power systems.
Cavity Voltage Phase Modulation MD
Mastoridis, Themistoklis; Molendijk, John; Timko, Helga; CERN. Geneva. ATS Department
2016-01-01
The LHC RF/LLRF system is currently configured for extremely stable RF voltage to minimize transient beam loading effects. The present scheme cannot be extended beyond nominal beam current since the demanded power would exceed the peak klystron power and lead to saturation. A new scheme has therefore been proposed: for beam currents above nominal (and possibly earlier), the cavity phase modulation by the beam will not be corrected (transient beam loading), but the strong RF feedback and One-Turn Delay feedback will still be active for loop and beam stability in physics. To achieve this, the voltage set point will be adapted for each bunch. The goal of this MD was to test a new algorithm that would adjust the voltage set point to achieve the cavity phase modulation that would minimize klystron forward power.
On the specification of bus voltages and radial link transfer impedance modes
Energy Technology Data Exchange (ETDEWEB)
El-Sadik, F.M. [Khartoum Univ., Aljamaa, Khartoum (Sudan)
2010-07-01
No algebraic equation has been derived for the steady-state stability limit (SSSL) of radial power system components in terms of their resistive sectional impedance elements and associated scalar node voltage constraints. While many criterion have been developed in the literature for the steady state angle and voltage stability limits of systems with losses, speculation exists about certain advocated metrics for these systems in terms of stability reserve margins as a measure of the risk of blackout and the representation of reactance modes associated with Putman's model for synchronous machines. This paper presented the results of a generalized algebraic statement for the reactance modes under stability conditions in voltage-specified power system components cited in the single machine-infinite bus (SMIB) and the radial power link (RPL) systems. The direct analytical solution to the problem enabled the identification of 2 different constraint relations for the sending (E) and receiving-end voltage regulator (VR) voltages. The paper discussed the general SSSL function plan, conditions for SMIB system reactances, and index results for the voltage stability of radial lines. The results for the R2 influence and influence on radial compensation levels were also presented. Index results for non-operational reactance zones were provided. It was concluded that the algebraic solution in a full representation of system losses would enable identification of additional function discontinuities that might not reveal in a step-by-step numerical algorithm and that may account for the many unresolved transmission system phenomenon associated with SSSL predictions and capacitance compensation schemes. 11 refs., 1 tab., 5 figs., 3 appendices.
Resonance analysis in parallel voltage-controlled Distributed Generation inverters
DEFF Research Database (Denmark)
Wang, Xiongfei; Blaabjerg, Frede; Chen, Zhe
2013-01-01
Thanks to the fast responses of the inner voltage and current control loops, the dynamic behaviors of parallel voltage-controlled Distributed Generation (DG) inverters not only relies on the stability of load sharing among them, but subjects to the interactions between the voltage control loops o...
Directory of Open Access Journals (Sweden)
Juan Gualberto Boza Valerino
2012-07-01
Full Text Available En el trabajo se realiza una breve reseña histórica sobre los distintos programas utilizados en los estudios de los regímenes estacionarios y transitorios utilizados en la Unión Eléctrica (UNE. Se exponen los resultados obtenidos mediante el programa Análisis de los Sistemas de Potencia (PSAF, por sus siglas en inglés, adquirido recientemente por la Empresa de Proyectos (INEL. Se hace énfasis en los métodos estáticos empleados para el análisis de la estabilidad de la tensión: Curvas P-V, Curvas V-Q y el Análisis Modal. Se aplica un procedimiento establecido en el trabajo al caso de estudio, sistema de 14 barras de la IEEE. El procedimiento se ha desarrollado atendiendo a la información, los criterios de estabilidad de la tensión y los resultados que proporciona el programa PSAF. Los resultados obtenidos con el caso estudio utilizado se consideran adecuados al ser validado con la literatura revisada. In the work is carried out a brief historical review on the different programs used in the studies of the steady state and transient operation in the Electric Union. The results exposed are obtained by means of the program Power Systems Analysis Framework (PSAF, acquired recently for the Electricity engineering and Project-making enterprise (INEL. Emphasis is made in the static methods employees for the voltage stability analysis: P-V curves, V-Q curves and the Modal Analysis. A procedure is applied in the work to the, system of 14 bus of the IEEE. The procedure has beendeveloped assisting to the information, the approaches of voltage stability and the results that it provides the program PSAF. The results obtained with the case study used are considered appropriate when being validated with cases of the revised literature.
Indian Academy of Sciences (India)
P Dutt; Akhlaq Husain; A S Vasudeva Murthy; C S Upadhyay
2015-08-01
This is the second of a series of papers devoted to the study of ℎ- spectral element methods for three dimensional elliptic problems on non-smooth domains. The present paper addresses the proof of the main stability theorem.We assume that the differential operator is a strongly elliptic operator which satisfies Lax–Milgram conditions. The spectral element functions are non-conforming. The stability estimate theorem of this paper will be used to design a numerical scheme which give exponentially accurate solutions to three dimensional elliptic problems on non-smooth domains and can be easily implemented on parallel computers.
Medelius, Pedro J. (Inventor); Simpson, Howard J. (Inventor)
2002-01-01
A voltage transient recorder can detect lightning induced transient voltages. The recorder detects a lightning induced transient voltage and adjusts input amplifiers to accurately record transient voltage magnitudes. The recorder stores voltage data from numerous monitored channels, or devices. The data is time stamped and can be output in real time, or stored for later retrieval. The transient recorder, in one embodiment, includes an analog-to-digital converter and a voltage threshold detector. When an input voltage exceeds a pre-determined voltage threshold, the recorder stores the incoming voltage magnitude and time of arrival. The recorder also determines if its input amplifier circuits clip the incoming signal or if the incoming signal is too low. If the input data is clipped or too low, the recorder adjusts the gain of the amplifier circuits to accurately acquire subsequent components of the lightning induced transients.
Padma, Narayanan; Maheshwari, Priya; Bhattacharya, Debarati; Tokas, Raj B; Sen, Shashwati; Honda, Yoshihide; Basu, Saibal; Pujari, Pradeep Kumar; Rao, T V Chandrasekhar
2016-02-10
Influence of substrate temperature on growth modes of copper phthalocyanine (CuPc) thin films at the dielectric/semiconductor interface in organic field effect transistors (OFETs) is investigated. Atomic force microscopy (AFM) imaging at the interface reveals a change from 'layer+island' to "island" growth mode with increasing substrate temperatures, further confirmed by probing the buried interfaces using X-ray reflectivity (XRR) and positron annihilation spectroscopic (PAS) techniques. PAS depth profiling provides insight into the details of molecular ordering while positron lifetime measurements reveal the difference in packing modes of CuPc molecules at the interface. XRR measurements show systematic increase in interface width and electron density correlating well with the change from layer + island to coalesced huge 3D islands at higher substrate temperatures. Study demonstrates the usefulness of XRR and PAS techniques to study growth modes at buried interfaces and reveals the influence of growth modes of semiconductor at the interface on hole and electron trap concentrations individually, thereby affecting hysteresis and threshold voltage stability. Minimum hole trapping is correlated to near layer by layer formation close to the interface at 100 °C and maximum to the island formation with large voids between the grains at 225 °C.
Characterisation of the VELO High Voltage System
Rakotomiaramanana, B; Eklund, L
2008-01-01
The high voltage system supplies the bias voltage to the 88 silicon sensors which comprise the LHCb Vertex Locator (VELO). This note describes the results of the tests which have been performed on the hardware of the high voltage system of the VELO. Each individual test detailed in this note corresponds to a specific requirement of the system. These requirements arise primarily from ensuring the safety of the silicon sensors and the quality of the data taken from the VELO modules. The tests performed are in four categories: normal operation of the high voltage system; vercation of its stability under operation; discussion of its behaviour in failure modes; and details of operation at low voltage. Noteworthy issues, identified through the tests, include the behaviour of the high voltage modules at voltages below 9V, the current limit that can be applied during ramping of the voltage, and the speed with which the voltage is cut during failures of the system. The results of these tests provide high confidence th...
Characterisation of the VELO High Voltage System
Rakotomiaramanana, B; Parkes, C; Eklund, L
2008-01-01
The high voltage system supplies the bias voltage to the 88 silicon sensors which comprise the LHCb Vertex Locator (VELO). This note describes the results of the tests which have been performed on the hardware of the high voltage system of the VELO. Each individual test detailed in this note corresponds to a specific requirement of the system. These requirements arise primarily from ensuring the safety of the silicon sensors and the quality of the data taken from the VELO modules. The tests performed are in four categories: normal operation of the high voltage system; verification of its stability under operation; discussion of its behaviour in failure modes; and details of operation at low voltage. Noteworthy issues, identified through the tests, include the behaviour of the high voltage modules at voltages below 9V, the current limit that can be applied during ramping of the voltage, and the speed with which the voltage is cut during failures of the system. The results of these tests provide high confidence...
Institute of Scientific and Technical Information of China (English)
康盛亮
2001-01-01
Using the modified method of multiple scales, the nonlinear stability of a truncated shallow spherical shell of variable thickness with a nondeformable rigid body at the center under compound loads is investigated. When the geometrical parameter k is larger,the uniformly valid asymptotic solutions of this problem are obtained and the remainder terms are estimated.
DEFF Research Database (Denmark)
Balling, Morten
2003-01-01
The article gives an overview of twelve contributions to a seminar organised in March 2003 by SUERF in cooperation with the Central Bank of Malta. The contributions analyse from different perspectives the problems related to securing financial stability in the EU accession countries. Important to...
Institute of Scientific and Technical Information of China (English)
王志新; 杜珊珊
2011-01-01
Under the frame of the Euclidean spaces, the Lipschitz stability of scalarization problems for multiobjective programming by exploring the strong regularity of Kojima functions is investigated.%利用Kojima函数的正则性质研究了多目标规划问题的纯量化问题解的强Lipschitz稳定性．
Deb, S.; Chaplin, R.; Sohanpal, S.; Unwin, G.; Soni, R.; Lenotre, L.
2008-01-01
Background: Psychotropic medications are used to manage behaviour problems in adults with intellectual disability (ID). One group of psychotropic medication are mood stabilizers such as lithium and some antiepileptic drugs. Method: A comprehensive systematic review was performed to determine the evidence base for the effectiveness of mood…
van Waelvelde, Hilde; Oostra, Ann; DeWitte, Griet; van den Broeck, Christine; Jongmans, Marian J.
2010-01-01
Aim: The aim of this study was to investigate the stability of motor problems in a clinically referred sample of children with, or at risk of, autism spectrum disorders (ASDs), attention-deficit-hyperactivity disorder (ADHD), and/or developmental coordination disorder (DCD). Method: Participants were 49 children (39 males, 10 females; mean age 5y…
Directory of Open Access Journals (Sweden)
Zaid Garcia Sánchez
2013-06-01
Full Text Available En este trabajo se presenta un análisis de la influencia de la naturaleza de la carga en la estabilidad de tensión. El margen de carga es un índice considerado exacto para el análisis de la estabilidad de la tensión, sin embargo tradicionalmente se ha asumido la carga para obtener este índice como carga de potencia constante, esto no refleja fielmente el comportamiento de la misma cuando se deterioran las condiciones de tensión en el sistema eléctrico. Se demuestra la influencia del factor de potencia de la carga en la obtención del punto de máxima carga del sistema, así como la influencia de la misma en la obtención del punto de estabilidad por tensión y el punto de máxima carga. Se implementó un programa para la determinación en tiempo real del margen de carga. La metodología fue probada con sistemas de prueba de la IEEE y con un sistema real. In this paper an analysis of the influence of the nature of the load is presented in the stability tension. The load margin is an exact indices to analyses voltage stability, however traditionally it has been considered the load for obtain these indices as a constant power load, this does not show faithfully the behavior of the load when the condition of tension in the electric system are deteriorate. It is demonstrated the influence of the load power factor in the obtaining of the maximum power load of the system, such as the influence of this one in the obtaining of the stability point and maximum load point. This paper presents software to obtain the load margin for on-line studies. The methodology was tested with IEEE test systems and a real system.
Institute of Scientific and Technical Information of China (English)
邵瑶; 汤涌; 郭小江; 周勤勇
2011-01-01
基于2015年“三华”特高压规划电网的丰大运行方式，利用短路比和多馈入短路比指标分析了华东受端电网的强度，并讨论了受端系统网架调整和直流系统落点位置对短路比／多馈入短路比的影响。采用PSD-BPA暂态稳定程序，分析了华东受端电网在各种故障下的暂态电压稳定性。结果表明：直流系统落点位置对华东受端电网强度的影响较大；交直流系统单一故障、受端特高压交流通道和逆变站换流母线附近线路发生三相永久性短路跳双回故障，大部分直流系统双极闭锁均不会导致华东受端电网暂态电压失稳；锦屏-同里、锡盟-金坛、复龙-奉贤和溪洛渡-浙西特高压直流发生双极闭锁故障后，送端电网需采取切机措施才能保持系统稳定。%Based on the summer peak load operation mode of the planned ＂North China-Central China-East China＂ UHV power grid in 2015, there will be 10 HVDC transmission lines feeding into East China power grid. The strength of East China receiving-end power grid is analyzed by short circuit ratio （SCR） and multi-infeed short circuit ratio （MISCR）, and the impacts of network topology adjustment in receiving-end power grid and the positions where the multi-infeed DC transmission lines are connected with East China receiving-end power grid on SCR/MISCR are dissected. By use of PSD-BPA transient stability program, transient voltage stability of East China receiving-end power grid under various faults is analyzed. Analysis results show that the positions, where the multi-infeed DC transmission lines are connected with East China receiving-end power grid, greatly impacts the strength of the latter; all unipolar block faults occurred in DC systems, single faults occurred in AC/DC system, three-phase permanent short-circuit fault, which causes the tripout of two circuits, occurred in UHVAC transmission line of receiving-end system and that
Wind energy systems solutions for power quality and stabilization
Ali, Mohd Hasan
2012-01-01
Unlike conventional power plants, wind plants emit no air pollutants or greenhouse gases--and wind energy is a free, renewable resource. However, the induction machines commonly used as wind generators have stability problems similar to the transient stability of synchronous machines. To minimize power, frequency, and voltage fluctuations caused by network faults or random wind speed variations, control mechanisms are necessary. Wind Energy Systems: Solutions for Power Quality and Stabilization clearly explains how to solve stability and power quality issues of wind generator systems. Covering
Automatic voltage imbalance detector
Bobbett, Ronald E.; McCormick, J. Byron; Kerwin, William J.
1984-01-01
A device for indicating and preventing damage to voltage cells such as galvanic cells and fuel cells connected in series by detecting sequential voltages and comparing these voltages to adjacent voltage cells. The device is implemented by using operational amplifiers and switching circuitry is provided by transistors. The device can be utilized in battery powered electric vehicles to prevent galvanic cell damage and also in series connected fuel cells to prevent fuel cell damage.
Institute of Scientific and Technical Information of China (English)
邹志翔; 周克亮; 袁晓冬
2011-01-01
考虑风资源的随机性和所接入电网的结构特点，针对主流的双馈机组所构成的风电场，分析了风电场接入对接入点周边地区电网电压稳定性的主要影响，详细论述了风电场接入容量与电压稳定性的关系、电网出现大扰动时的暂态稳定性以及风电场低电压穿越能力。在此基础上，提出了改善电压稳定性的相关措施，研究了静止同步补偿器（static synchronous compensator，STATCOM）接入对电压稳定性的改善效果及其接入容量的选取。在DigSILENT／Powerfactory仿真平台对上述问题进行了仿真实验。结果表明：风电场接入容量过大，不利于地区电压稳定；为防止电网扰动时的电压失稳，一般应要求风电场具有低压穿越能力；合理地进行就地无功补偿有助于提高地区电压稳定性。%Considering the randomness of wind power source and structural features of power network connected with wind farm, the main influences of connecting wind power system consisting of doubly fed induction generators （DFIG） to power grid on voltage stability of local power network neighboring to connection point are analyzed. The relationship between wind farm capacity being connected to power grid and voltage stability, transient voltage stability under large disturbance occurred in power grid and low voltage ride through of wind farm are expounded. Based on the analysis results, the measures to improve voltage stability are proposed. The improving effect of static synchronous compensator （STATCOM） on voltage stability and the selection of the capacity of STATCOM are researched. Above-mentioned issues are simulated on DigSILENT/Powerfactory platform. Simulation results show that too large capacity of wind farm being connected to power grid is adverse to voltage stability of local power network neighboring to the connection point of wind farm; to prevent voltage instability under power grid
Panwar, Ramesh; Rennels, David; Alkalaj, Leon
1993-01-01
A technique for minimizing the power dissipated in a Very Large Scale Integration (VLSI) chip by lowering the operating voltage without any significant penalty in the chip throughput even though low voltage operation results in slower circuits. Since the overall throughput of a VLSI chip depends on the speed of the critical path(s) in the chip, it may be possible to sustain the throughput rates attained at higher voltages by operating the circuits in the critical path(s) with a high voltage while operating the other circuits with a lower voltage to minimize the power dissipation. The interface between the gates which operate at different voltages is crucial for low power dissipation since the interface may possibly have high static current dissipation thus negating the gains of the low voltage operation. The design of a voltage level translator which does the interface between the low voltage and high voltage circuits without any significant static dissipation is presented. Then, the results of the mixed voltage design using a greedy algorithm on three chips for various operating voltages are presented.
Silicone elastomers with aromatic voltage stabilizers
DEFF Research Database (Denmark)
A Razak, Aliff Hisyam; Skov, Anne Ladegaard
and benzene rings in PDMS-PPMS copolymer was measured by UV-vis spectroscopy. The developed elastomers were inherently soft with enhanced electrical breakdown strength due to delocalized pi-electrons of aromatic rings attached to the silicone backbone. The dielectric relative permittivity of PDMS...
Silicone elastomers with aromatic voltage stabilizers
DEFF Research Database (Denmark)
A Razak, Aliff Hisyam; Skov, Anne Ladegaard
breakdown strength, the storage modulus and the loss modulus of the elastomer were investigated, as well as the excitation energy from the collision between electron carriers and benzene rings in PDMS-PPMS copolymer was measured by UV-vis spectroscopy. The developed elastomers were inherently soft...
Silicone elastomers with aromatic voltage stabilizers
DEFF Research Database (Denmark)
A Razak, Aliff Hisyam; Skov, Anne Ladegaard
, as well as the excitation energy from the collision between electron carriers and benzene rings in PDMS-PPMS copolymer was measured by UV-vis spectroscopy. The developed elastomers were inherently soft with enhanced electrical breakdown strength due to delocalized pi-electrons of aromatic rings attached...
Voltage Stability in Power system Using STATCOM
Directory of Open Access Journals (Sweden)
Mr. D.K. Sharma
2012-03-01
Full Text Available the current major restructuring of the electricity market and the advances of new technology add new complexities in the power system applications software, particularly optimization. Minimization of the impact of a transaction on unrelated third party facilities or maximization of the power transfer between utilities needs now to be formulated as new constraints or objective functions. The dispatch and control of generating units, the taps of regulating transformers, mechanically switched capacitors and reactors have been the primary means available for controlling power flows over the years. However, certain applications require frequent operations that result in a rapid wearing out of the switching equipment. The inadequate line flow control may result in overloaded parts of the networks, while other parts are loaded far below their power carrying capacity. Therefore, the demands for flexibility in power flow control are growing continuously. The FACTS relying on thyristors have high speed switching capability that allows for rapid readjustment of line power flows in response to various contingencies. Installation of FACTS devices on key locations in a meshed network changes the effective reactance of the parallel paths and consequently the way that power divides among them. This paper proposes study of various FACTS DEVICES that can be installed. FACTS DEVICES model isincorporated into a Newton-Raphson algorithm to perform load flow analysis. Proposed algorithm is tested on IEEE 30 bus power system for optimal allocation of STATCOM and results are presented.
Verma, H. K.; Mafidar, P.
2013-09-01
In view of growing concern towards environment, power system engineers are forced to generate quality green energy. Hence the economic dispatch (ED) aims at the power generation to meet the load demand at minimum fuel cost with environmental and voltage constraints along with essential constraints on real and reactive power. The emission control which reduces the negative impact on environment is achieved by including the additional constraints in ED problem. Presently, the power system mostly operates near its stability limits, therefore with increased demand the system faces voltage problem. The bus voltages are brought within limit in the present work by placement of static var compensator (SVC) at weak bus which is identified from bus participation factor. The optimal size of SVC is determined by univariate search method. This paper presents the use of Teaching Learning based Optimization (TLBO) algorithm for voltage stable environment friendly ED problem with real and reactive power constraints. The computational effectiveness of TLBO is established through test results over particle swarm optimization (PSO) and Big Bang-Big Crunch (BB-BC) algorithms for the ED problem.
Institute of Scientific and Technical Information of China (English)
刘武旭
2012-01-01
This paper introduces the functions of the stability control equipment in Guohua Ningdong Power Plant.The possible problems in the operation of the stability control equipment in the 330kv substation wring mode are analyzed and the corresponding measures are proposed.%简要介绍了国华宁东电厂安稳装置的作用、功能。针对宁东电厂330KV变电站接线方式,对安稳装置运行中可能出现的问题进行了分析并提出了解决方案。
Wu, Zhongzhen; Ji, Shunping; Liu, Tongchao; Duan, Yandong; Xiao, Shu; Lin, Yuan; Xu, Kang; Pan, Feng
2016-10-12
Layered transition-metal oxides (Li[NixMnyCoz]O2, NMC, or NMCxyz) due to their poor stability when cycled at a high operating voltage (>4.5 V) have limited their practical applications in industry. Earlier researches have identified Mn(II)-dissolution and some parasitic reactions between NMC surface and electrolyte, especially when NMC is charged to a high potential, as primarily factors responsible for the fading. In our previous work, we have achieved a capacity of NMC active material close to theoretical value and optimized its cycling performance by a depolarized carbon nanotubes (CNTs) network and an unique "pre-lithiation process" that generates an in situ organic coating (∼40 nm) to prevent Mn(II) dissolution and minimize the parasitic reactions. Unfortunately, this organic coating is not durable enough during a long-term cycling when the cathode operates at a high potential (>4.5 V). This work attempts to improve the surface protection of the NMC532 particles by applying an active inorganic coating consisting of nanosized- and crystal-orientated LiFePO4 (LFP) (about 50 nm, exposed (010) face) to generate a core-shell nanostructure of Li(NixMnyCoz)O2@LiFePO4. Transmission electron microscopy (TEM) and etching X-ray photoelectron spectroscopy have confirmed an intimate contact coating (about 50 nm) between the original structure of NMC and LFP single-particle with atomic interdiffusion at the core-shell interface, and an array of interconnected aligned Li(+) tunnels are observed at the interface by cross-sectional high-resolution TEM, which were formed by ball-milling and then strictly controlling the temperature below 100 °C. Batteries based on this modified NMC cathode material show a high reversible capacity when cycled between 3.0 and 4.6 V during a long-term cycling.
Voltage sag source location based on instantaneous energy detection
DEFF Research Database (Denmark)
Chen, Zhe; Xinzhou, Dong; Wei, Kong
2007-01-01
Voltage sag is the major power quality problem, which could disrupt the operation of sensitive equipment. This paper presents the applications of instantaneous energy direction for voltage sag source detection. Simulations have been performed to provide the analysis for system with distributed ge...... generation units. The studies show that the presented method can effectively detect the location of the voltage sag source....
Mitigation Voltage Sag in Power System by Static Synchronous Compensator
Directory of Open Access Journals (Sweden)
Prechanon Kumkratug
2010-01-01
Full Text Available Problem statement: The disturbance in power system is unavoidable situation. It cause in voltage sag in power system. Approach: This study applied the STATCOM to mitigate voltage of the system. The mathematical model of power system equipped with a STATCOM is systematically derived. The presented mathematical model is shown how it effects on voltage sag improvement. The simulation results are tested on a Single Machine Infinite bus. The proposed method is equipped in sample system with severe disturbance. The variation voltage of the system without and with a STATCOM is plotted and compared. Results: It was found that the system without a STATCOM has high voltage variation especially voltage sags whereas with a STATCOM the system voltage has small voltage sages. Conclusion: From the simulation results, the STATCOM can mitigate voltage of power system.