Dynamic Voltage Stability Research Articles

The Research of Voltage Stability in Wind Power System

Wind power is a kind of special electric power, because of the volatility of the wind, making voltage stability has become an important research problem wind power system must facing with. Therefore, according to the relevant current research status and the main existent problems of wind power system, expounding the difference of voltage stability between the conventional energy sources and the wind power, and the influence of voltage stability to the power system which caused by wind power system. This paper mainly from the definition and the classification to introduce the voltage stability; from the research contents and methods of static and dynamic voltage stability to analyze power systems which contains wind farms, especially emphasizing the necessity of the bifurcation theory used in power system contains wind power. Finally points out that the research trend of analysis and improvement in this area.

A Full Dynamic Voltage Stability Research Based on Time-domain Simulation

The voltage stability is substantially a dynamic stability, but the primary method which is more mature and engineering practical to analyze the stability of voltage is still static analysis. The time-domain simulation is an important measure in research of complex power grid. With the development of full dynamic simulation technology, the research of dynamic voltage stability by using full dynamic simulation program which is based on time-domain simulation can be carried out. This paper uses full dynamic simulation program in dynamic voltage stability research, lays special stress on research in how generator over-excitation limiter functioned and influence in dynamic voltage stability research, and raise 2 methods and steps to figure out dynamic stable voltage in both over-excitation counted and not counted. The simulation results of examples indicate the correctness and effectiveness of these methods, and also fully verify the function and influence of generator over-excitation limiter in full dynamic voltage stability research.

Robust control strategy for PV system integration in distribution systems

This paper proposes a decentralized control strategy for higher penetration of photovoltaic (PV) units without violating system operating constraints. A systematic procedure is developed and a robust controller is designed to ensure both dynamic voltage and transient stability for a specific PV integration level. The change in the model due to the volatile nature of PV generations is considered as an uncertain term in the design algorithm. Simultaneous output-feedback linear quadratic controllers are designed for PV generators. This designed control scheme is robust with respect to intermittency and enhances the integration level in a sub-transmission and distributed system. The effectiveness of the proposed controller is verified on a 43-bus industrial meshed distribution system under large disturbances. It is found that the designed control scheme enhances stability and increases the renewable integration levels.

Dynamic voltage stability constrained congestion management framework for deregulated electricity markets

Congestion management is an important part of power system operation in today deregulated electricity markets. However, congestion management is traditionally performed based on static analysis tools, while these tools may not correctly capture dynamic voltage stability limits of a power system. In this paper, a new congestion management framework considering dynamic voltage stability boundary of power system is proposed. For this purpose, precise dynamic modeling of power system equipment, including generators and loads, is incorporated into the proposed congestion management framework. The proposed method alleviates congestion with a lower congestion management cost and more dynamic voltage stability margin, resulting in a more robust power system, compared with the previous congestion management methods. The validity of proposed congestion management framework is studied based on the New England 39-bus power system. The obtained results confirm the validity of the developed approach.

A Novel Arnoldi Method to Calculate the Critical Eigenvalues in Power System

Hopf bifurcation is regarded as one of the three kinds of bifurcations which can cause voltage instability. The Hopf bifurcation was obtained if a pair of complex conjugate eigenvalues of Jacobian matrix crossing the imaginary axis. To calculate the critical eigenvalues of bulk power system, a restarted-refined Arnoldi method is introduced. The refined Ritz vectors are used as the approximations based on the refined projection theory in order to enrich the information of the eigenvectors in the projective subspace. Two examples indicate that the method can work out a set of conjugate eigenvalues which will show whether the Hopf bifurcation appears and provide the datum for the dynamic voltage stability analysis ulteriorly.

Dynamic Voltage Stability Analysis for Power Systems with Wind Power Plants using Relative Gain Array (RGA)

This paper concerns the use of relative gain array (RGA) for analyzing the interactions among the wind power plant voltage controller and power system traditional voltage stability controllers. RGA analyses for both static and dynamic voltage stability controls are carried out based on the multi-input multi-output (MIMO) transfer function matrix J v (s). By means of the singular value and RGA, the dynamic voltage stability and their controller interactions are analyzed and the dynamic voltage stability control loop selection can be realized. A multi-machine power system with a wind power plant is simulated for the demonstration of the proposed approach. The proposed approach takes the advantages of the classical static voltage stability analysis and the modern multi-variable feedback control theory. This proposed approach is simple and can be easily implemented into large power systems with distributed wind power plant voltage controllers.

Weakest Bus Identification Based on Modal Analysis and Singular Value Decomposition Techniques

Voltage instability problems in power system is an important issue that should be taken into consideration during the planning and operation stages of modern power system networks. The system operators always need to know when and where the voltage stability problem can occur in order to apply suitable action to avoid unexpected results. In this paper, a study has been conducted to identify the weakest bus in the power system based on multi-variable control, modal analysis, and Singular Value Decomposition (SVD) techniques for both static and dynamic voltage stability analysis. A typical IEEE 3-machine, 9-bus test power system is used to validate these techniques, for which the test results are presented and discussed.

Weakest Bus Identification Based on Modal Analysis and Singular Value Decomposition Techniques

Voltage instability problems in power system is an important issue that should be taken into consideration during the planning and operation stages of modern power system networks. The system operators always need to know when and where the voltage stability problem can occur in order to apply suitable action to avoid unexpected results. In this paper, a study has been conducted to identify the weakest bus in the power system based on multi-variable control, modal analysis, and Singular Value Decomposition (SVD) techniques for both static and dynamic voltage stability analysis. A typical IEEE 3-machine, 9-bus test power system is used to validate these techniques, for which the test results are presented and discussed.

A Synchrophasor Assisted Frequency and Voltage Stability Based Load Shedding Scheme for Self-Healing of Power System

This paper presents a new scheme for load curtailment in the power system required for its self-healing under critical contingencies, which may pose a threat to frequency as well as the voltage stability of the system. The load shedding requirement in the system has been calculated based on the computed disturbance power as well as the voltage stability condition of the system, with the aid of real-time data, assumed to be available from the synchrophasor based wide area monitoring and control system (WAMCS). This scheme assesses voltage stability based on a dynamic voltage stability criterion, formulated using a Voltage Stability Risk Index (VSRI). Suitable locations for the load curtailments have been chosen according to the VSRI, calculated at each load bus. Performance of the proposed scheme has been tested on New England 39-bus system and a practical 246-bus Indian system. The results are compared with a conventional under frequency load shedding scheme and an adaptive load shedding scheme.

Adaptive Scheme for Minimal Load Shedding Utilizing Synchrophasor Measurements to Ensure Frequency and Voltage Stability

This article presents a new scheme for load curtailment in the power system under critical contingencies that may pose a threat to the frequency and voltage stability of the system. The proposed scheme is based on a two-stage load-shedding strategy. In the first stage, disturbances have been classified based on the computed value of the disturbance power, and the load-shedding requirement in the system has been assessed based on the frequency stability, as well as dynamic voltage stability, conditions. The scheme assumes the availability of real-time data from a synchrophasor-based wide area monitoring and control system. A dynamic voltage stability criterion has been developed in this stage using a voltage stability risk index to assess the voltage stability in real time. Suitable locations for the load curtailments have been chosen according to the voltage stability risk index, which is calculated at each load bus. After the system attains transient stability, the second stage of the proposed scheme determines the optimal redispatching of generators for recovering the loads as much as possible, which had been curtailed in the first stage following the contingency. Performance of the proposed scheme has been tested on a 10-machine, New England 39-bus system, and the results are compared with a conventional under-frequency load-shedding scheme and an adaptive load-shedding scheme.

Dynamic voltage stability prediction of power systems by a new feature selection technique and probabilistic neural network

With continued increase in the electrical energy demand and tendency towards maximizing economic benefits in power transmission system, especially in the liberalized electricity markets, real-time voltage security analysis has become a growing concern in electric power utilities. However, static analysis methods, such as power flow based methods, have difficulty in evaluating voltage stability and some voltage stability feasible region boundaries may not be correctly analyzed by these methods due to the use of simple models for the system components. On the other hand, dynamic modeling and evaluation of voltage stability are complex, expensive, and time consuming. In this paper, a new feature selection technique combined with a probabilistic neural network (PNN) is proposed for this purpose. A major difference of our paper with the previous research works in the area is that this paper proposes voltage stability prediction, while the previous works usually focus on the voltage stability evaluation. The proposed dynamic voltage stability prediction method is examined on the IEEE 14-bus and New England 39-bus test systems and the effectiveness of the proposed method is demonstrated. Also, the effect of different load models, branch contingencies, and generator contingencies is evaluated. Another advantage of the proposed prediction method is that it can be used for varied topologies and configurations of the power system. Copyright © 2010 John Wiley & Sons, Ltd.

Decentralized robust static synchronous compensator control for wind farms to augment dynamic transfer capability

This paper presents an algorithm to design a decentralized robust controller for static synchronous compensators (STATCOMs) using minimax linear quadratic output-feedback control design approach. There is an increase in the available (dynamic) transfer capability of power systems with fixed-speed wind generators due to the designed decentralized controllers. The effects of the integration of various types of wind generators into power systems based on transfer limit have also been analyzed in this paper. The effectiveness of the suggested control strategy is validated by simulations on a benchmark two area power system. The performance of the designed controller is also compared to a conventional proportional-integral-based STATCOM controller. Simulation results show that both the dynamic voltage stability and the transient stability can be improved by using the robust STATCOM control proposed in this paper.

Real Time Wide Area Voltage Stability Index in the Korean Metropolitan Area

Through the development of phasor measurement units (PMU), various aspects of power system dynamic behavior could be monitored and diagnosed. Monitoring dynamic voltage stability has become one of the achievements we can obtain from PMUs. It is very important to select the most appropriate method for the Korea Electric Power Corporation (KEPCO) system since there are many voltage stability indices. In this paper, we propose an advanced WAVI (Wide Area Voltage Stability) that is well suited for the purposes of monitoring the dynamic voltage stability of KEPCO’s PMU installation plan. The salient features of the proposed index are: i) it uses only PMU measurements without coupling with EMS data; ii) it is computationally unburdened and can be applied to real-time situations. The proposed index is applied to the KEPCO test system and the results show that it successfully predicts voltage instability through comparative studies.

Load Characteristics Effect on Dynamic Voltage Stability Analysis in HVDC Systms (Dept.E)

The modeling of loads has a significant effect on the accuracy of dynamic voltage stability analysis of HVDC system. This paper investigates the dynamic nature of voltage instability considering static and dynamic load models. The load effect al different control modes of HVDC system is considered for different configurations of single infeed HVDC systems at different effective short circuit ratios. The results are validated using nonlinear simulations.

Dynamic voltage stability assessment of power transmission systems using neural networks

Abstract With increased loading and exploitation of power transmission systems, voltage stability has become a growing concern in electric power utilities. Static analysis methods, such as power flow based methods, have difficulty in evaluating voltage stability due to using simple models for the system components. On the other hand, dynamic modeling and evaluation of voltage stability are complex, expensive and time consuming. In this paper, a neural network (NN) approach is presented for this purpose. This NN can establish a mapping between the operating conditions and the dynamic voltage stability margin (VSM) of each bus. This analysis gives an insight about the robustness of various buses and dynamic voltage security status of the power system. The method is examined on Iran’s North-West Transmission Network, and a mean absolute estimation error of 2.3% and a response time less than 0.1 s are obtained. By comparing the results obtained through different methods, it is concluded that the NN approach provides a compromise between accuracy and speed of calculations. Hence, for operational purposes, for which having fast response is vital, using the NN approach is recommended. On the other hand, for the design and development of power systems, using dynamic simulation seems a better approach due to its higher accuracy.

Dynamic voltage stability constrained ATC calculation by a QSS approach

Abstract The evaluation of Available Transfer Capability (ATC) in deregulated power system should take into account thermal limits, transient, steady-state and dynamic angle stability as well as the voltage stability limit. The consideration of voltage stability in the determination of ATC, however, was not well researched before. On the other hand, under the power market environment, voltage instability becomes a more important consideration in many countries in recent years, especially when following a large disturbance in a heavily stressed power system over long distances. A new ATC determination scheme using Quasi-steady-state (QSS) approximation is proposed in this paper and implemented on a test system. The performance of the QSS approximation is also compared with the Full-Time-Scale (FTS) simulation. From the results, it is shown that the proposed scheme can evaluate ATC with dynamic voltage stability constraints accurately and the calculation speed is accelerated considerably to meet the real-time requirement.

Optimal Placement of SVC for Static and Dynamic Voltage Security Enhancement

This paper presents a sensitivity based approach to determine optimal location of Static VAR Compensator (SVC) for voltage security enhancement. The proposed approach of SVC placement computes sensitivity of system loading factor with respect to reactive power generation, derived from reactive power balance equation. This sensitivity factor has been termed as Bus Static Participation Factor (BSPF). The sensitivity of the most critical eigen value with respect to bus voltage magnitude has been considered as Bus Dynamic Participation Factor (BDPF). BSPF and BDPF have been combined to obtain Bus Hybrid Participation Factor (BHPF), which have been computed for the system intact case and critical contingency cases and used for selecting the optimal site for the SVC installation. The effectiveness of the proposed approach of SVC placement has been validated on a practical 75-bus Indian system with respect to enhancement of the static as well as dynamic voltage stability margins.

Improving Voltage Stability by Reactive Power Reserve Management

The amount of reactive reserves at generating stations is a measure of the degree of voltage stability. With this perspective, an optimized reactive reserve management scheme based on the optimal power flow is proposed. Detailed models of generator limiters, such as those for armature and field current limiting must be considered in order to utilize the maximum reactive power capability of generators, so as to meet reactive power demands during voltage emergencies. Participation factors for each generator in the management scheme are predetermined based on the voltage-var (V-Q) curve methodology. The Bender's decomposition methodology is applied to the reactive reserve management problem. The resulting effective reserves and the impact on voltage stability are studied on a reduced Western Electric Coordinating Council system. Results prove that the proposed method can improve both static and dynamic voltage stability.

Automatic Reactive Power Control of Isolated Wind-Diesel Hybrid Power Systems for Variable Wind Speed/Slip

In this article, automatic reactive power control of an isolated wind-diesel hybrid power system having an induction generator coupled with wind turbine for power generation is presented. The mathematical model of the system using reactive power flow equations is developed. The dynamic voltage stability evaluation is based on small signal analysis considering a typical static VAR compensator (SVC) and IEEE type-I excitation system. It is shown that a variable reactive power source, like SVC, is a must to meet the varying demand of reactive power by induction generator and load and to obtain a very good voltage regulation of the system with minimum fluctuations. Integral square error (ISE) criterion is used to evaluate the optimum setting of gain parameters. Finally, the dynamic responses of the sample power system considered with optimum gain setting are also presented.

A Novel Mathematical Modelling of Induction Generator for Reactive Power Control of Isolated Hybrid Power Systems

This article considers automatic reactive power control of an isolated wind-diesel hybrid power system having an induction generator as a power conversion device for wind power generation. The mathematical model of induction generator and complete system using reactive power flow equations is developed. The dynamic voltage stability evaluation is based on small-signal analysis considering a typical Static VAR Compensator (SVC) and IEEE type-I excitation system. It is shown that a variable reactive power source like SVC is necessary to meet the varying demand of reactive power by induction generator and load and to obtain very good voltage regulation of the system with minimum fluctuations. Integral square error (ISE) criterion is used to evaluate the optimum setting of gain parameters. Finally, the dynamic responses of the power systems considered with optimum gain setting are presented.