System Voltage Stability Research Articles

Application of mutation inspired constrained factor PSO considering voltage stability and losses by locating and rating TCSC during N-1 contingency

This paper describes, a strategy for optimal placement and setting of series FACTS controller thyristor controlled series capacitor (TCSC) under single line contingency (N-1) using particle swarm optimisation (PSO), constriction factor PSO (CFPSO), Cauchy mutation-CFPSO (CM-CFPSO) and Gaussian mutation-CFPSO (GM-CFPSO) algorithm in order to reduce over loading and power loss in transmission lines and to improve voltage stability of a power system. In this proposed CM-CFPSO and GM-CFPSO methods, a new-fangled position equation is framed and the features of the constriction factor approach (CF) is incorporated with the proposed approach. To detect the most severe transmission line, composite severity index (COSI) is calculated under N-1 contingency and top three severe lines are taken for this research work. To validate the consequence of proposed approach, simulation studies are carried out on a standard IEEE 30-bus network. Appraisals are made in provisions of eminence solution, execution time and stable convergence behaviour.

Parameters Identification of Induction Motor Model Based on Manufacturer Data and Sequential Quadratic Programming

In order to precaution and control the transient voltage stability of the receiving-end system, it is very necessary to quickly and accurately calculate the model parameters for induction motor synthesis load. There are several methods to obtain the model parameters of induction motor, in which, estimating the model parameters of induction motor using for power system stability analysis according to the nameplate data is a significant promising approach with potential application. In this paper, a new optimized mathematical model for identification of induction motor single-cage and double-cage parameters are proposed, it’s overcome the deficiency of artificially adding approximate constraints in parameter identification of induction motor models from induction motor manufacturer data. Minimization of the induction motor efficiency deviation is taken as the goal and important induction motor performance indicators, such as the stator current, the input reactive power, the maximum electromagnetic torque and the starting parameters, are equal to their manufacturer values are regarded as constraints, the sequential quadratic programming (SQP) is used to solve the nonlinear problem. The proposed new mathematical model and algorithm were verifed on a sample of 6 induction motors of different capacity, manufacturers, and rated voltage. The induction motor performance characteristics supplied by the manufacturer and used to identification parameters of induction motor are then calculated, using the equivalent circuit estimated parameters themselves. In all the studied cases, the calculated induction motors performance indexes are found to be in excellent agreement with the manufacturer data. Comparison with other methods shows that the induction motor model parameters obtained by this method can reflect the working characteristics of induction motor single-cage and double-cage model more accurately.

Distributed parameter-based voltage stability index for identification of critical lines and voltage stability margin in power system

This paper proposes a distributed parameter-based voltage stability index (DPVSI) for assessment of voltage stability of the power system. Proposed index incorporates the effects of distributed par...

Gravitational Search Algorithm Based Technique for Voltage Stability Improvement

<p>Voltage instability problem has been known as a significant threat to power system operation since its occurrence can lead to power interruption. This phenomenon can be due to uncontrollable load increment, line and generator outage contingencies or unplanned load curtailment. Optimal reactive power dispatch involving reactive power support can be one of the options for improving voltage stability of a power system, which also requires optimization process. Optimal sizing and location can of reactive power support can avoid the system from experiencing over-compensated or under-compensated phenomena. The presence of optimization techniques has helped solving non-optimal phenomenon, nevertheless some setbacks have also been experienced in terms of inaccuracy and stuck in local optima. This paper presents the application of Gravitational Search Algorithm (GSA) technique in attempt to solve optimal reactive power dispatch problem in terms of reactive power support for voltage stability improvement. Optimization process tested on IEEE 14-bus Reliability Test System (RTS) has revealed its superiority with significant promising results in terms of voltage stability improvement in the test system. </p>

Impact of current-controlled voltage source converters on power system stability

Abstract It is known that current-controlled voltage source converters do not contribute to the inertia of power systems, leading to a higher rate of change of frequency in case of power imbalances. Another fundamental effect becomes apparent in case of large phase angle jumps of the grid voltage. Such phase angle jumps may occur, for example, in consequence of a system split. The power infeed of the converter depends on the estimated phase angle and, hence, is transiently influenced by the inherent delay of its estimation, usually by a phase-locked loop (PLL). This paper investigates the effect of the PLL dynamics on the converter behavior and its impact on transmission system voltage and frequency stability. To this end, islanding scenarios of a grid with lines loaded beyond their natural power are considered. Sensitivity analyses of the PLL parameters show noticeable effects on voltage and frequency stability depending on the dynamic parameterization of the PLL.

A Review on Optimal Allocation and Sizing Techniques for DG in Distribution Systems

Distributed Generation (DG) offers the reliable and economic source of electricity to consumers. These are connected directly to the distribution system at consumer load points. Integration of DG units into an existing system has significantly high importance due to its innumerable advantages. However, Optimal DG (ODG) allocation and sizing is always a challenging task for utilities as well as consumers. The major objective of ODG allocation and sizing is to improve system overall efficiency with minimum power loss, maximum system security, voltage stability, and reliability. Analytical techniques are performing well for small and simple systems, not suitable for a system with large and complex networks. However, various meta-heuristic techniques are performing better in terms of accuracy and convergence for extensively large and complex networks. A hybrid optimization is a combination of two or more optimization techniques. This technique offers efficient and reliable global optimum solutions for complex multi-objective problems. In this context, a comprehensive literature review of DG fundamentals and the different technical approaches for DG integration into the distribution system are analyzed here. Furthermore, an attempt has been made for comparison of analytical, classical (non-heuristic), meta-heuristic and hybrid optimization techniques with respect to objective function, test system, advantages, and disadvantages. This present study will give in-depth knowledge and acts as a forthright reference for imminent investigators and investors for ODG allocation and sizing in a distribution system.Â

Study on the Evaluation Index System and Evaluation Method of Voltage Stability of Distribution Network with High DG Penetration

With the development of new energy technologies, distributed generation (DG) plays a growing role in power distribution networks. Although it solves the power supply problem in some areas, it also poses a challenge to the traditional power grid. To help with this problem, we establish a static voltage stability analysis model for high penetration DG, taking into account its large capacity, and the high fluctuations of its output. Based on the theoretical analysis and the mathematical derivation, we propose an improved voltage stability evaluation index (IVSE) accounting for DG. Finally, using the typical circuit of the IEEE 33 & 69 node system, we simulate high penetration DG access in different locations and capacities. In the simulations, the traditional power flow equation is modified by a continuous parametric equation accounting for DG. Based on consideration of the system transmission power limit, voltage stability margin and system loss, the value of IVSE is demonstrated, in comparison with the traditional index. Thus, we verify that the IVSE index is easy to understand, simple to calculate, and highly versatile.

Impact of Thyristor Controlled Series Capacitor on Voltage Profile of Transmission Lines using PSAT

In power system voltage stability is very important in order to maintain the voltage within the defined limits. The demand of electrical power increases in the last decade due to the lack of expansion in the generation and transmission network. The available transmission network is heavily loaded. This loading of transmission network cause the voltage instability. This instability on heavy loaded system creates voltage collapse which causes the power loss. Due to this phenomenon it is necessary to keep monitoring the voltage instability and to reduce voltage collapse. Voltage collapse mostly occurs due to the minimum availability of the reactive power. A power electronic device i.e. Flexible AC Transmission System (FACTS) is used to add the reactive power to the system which improve the voltage profile and minimizes the chances due to which the voltage collapse occur. In this paper FACTS series compensator, i.e. Thyristor Controlled Series Capacitors (TCSC) is injected between the two nodes of the IEEE 6 bus bar test system to check the voltage profile. PSAT (Power System Analysis Tool) tool, which is a new tool in MATLAB for study in power system analysis is used. IEEE-6 bus system is used as a test system for the effectiveness of the proposed method. The voltage profile with and without TCSC device is then compared to conclude the result.

Bi-Objective Reactive Power Reserve Optimization to Coordinate Long- and Short-Term Voltage Stability

Reactive power reserve (RPR) management is a critical issue to power system voltage stability. Two RPR definitions are first proposed in this paper to evaluate the levels of RPR and improve voltage stability, namely long-term voltage stability-related RPR (LVRPR) and short-term voltage stability-related RPR (SVRPR). Both definitions consider two factors: 1) the RPR of each online generator and 2) the relative contribution of the RPR to voltage stability varying with location and scenario. For LVRPR, the generator participation factor is used to describe the contributions of RPR. For SVRPR, an voltage support coefficient considering the generator’s dynamics is proposed to evaluate the RPR’s contribution. In normal condition, short-term voltage stability is expected to be improved by the optimization of SVRPR, ensuring enough long-term voltage stability margin. A bi-objective optimization model that coordinates LVRPR and SVRPR is formulated to enhance long- and short-term voltage stabilities simultaneously. The proposed model is solved using the normal boundary intersection technique. The proposed method is performed using an IEEE39-bus system, and the results show that the optimal solution improves both long- and short-term voltage stabilities by optimizing the trade-off between LVRPR and SVRPR.

A Method to Estimate Power System Voltage Stability Margins Using Time-Series From Dynamic Simulations With Sequential Load Perturbations

In this paper, a methodology to assess power system voltage stability margins from time-series data is presented. The proposed method obtains time-series from dynamic simulations subject to sequential load changes that are then used as an input to a voltage stability estimation method. After a contingency is applied, load perturbations aim to move the system through different loading levels. This approach allows estimating voltage stability margins from time-series without any information or numerical quantities of the mathematical model of the system other than the simulation’s output. This is useful for dynamic security assessment systems that only have transient simulators for their workflows and still require to estimate the voltage stability margins. The proposed method is used to quantify the severity of the contingencies using a three-layer index. The proposed approach is illustrated using a simple two-bus system and then tested using time-domain simulations of the Nordic-44 Bus test system.

A predictive agent-based scheme for post-disturbance voltage control

In this paper a predictive scheme for dynamic voltage control is proposed, which maintains voltage security (both voltage stability and voltage profile) of power system, in a wide area manner. The proposed algorithm, upon detecting any voltage violation (both under- and/or over-voltages), employs organized multi-agent system (OMAS) in order to coordinate the employment of reactive power devices in returning voltage magnitudes of all buses to the acceptable range and steady behaviour. In order to achieve high benefits of power system response, each agent takes advantage of a predictive scheme, which is based on the corresponding bus voltage trend. By this predictive characteristic, each agent coordinates its command for remedial action with the prediction of bus voltage destination. Moreover, this predictive characteristic is extended to consider incoming remedial actions (or to compensate the latency in activation of previously decided remedial actions). These predictive characteristics lead to making a smooth waveform and reducing the number of needed remedial actions. The performance of the proposed scheme against different scenarios in Nordic32 test system is presented, where the results illustrate effectiveness and robustness of the proposed scheme.

Optimal location strategy for distributed generation to maximize system voltage stability based on line sensitivity factors

This paper presents a combination strategy to determine the optimal location of PV distributed generation units (PV-DGs) in terms of maximizing the power system voltage stability level. The voltage collapse power indices (VCPIs) is chosen to access the voltage stability level of a system. To eliminate the need of iterations, a new line power flow calculation method based on the line sensitivity factors (LSFs) is developed. It could precisely compute out VCPI without executing AC power flow program. Combined with the economic optimization software HOMER to determine the sizes and quantities of PV-DGs, the optimal buses to connect PV-DGs are selected by minimizing the sum of VCPIs. The proposed location strategy is validated by multiple IEEE test systems. The numerical simulation results demonstrate that the proposed method is accurate on VCPI calculations and has the decreased computation time compared with the Newton-Raphson power flow method. Through the continuous power flow results, it is verified that the optimal DG configuration selected by the proposed strategy could maximize the overall voltage stability margin of the system.

Hierarchical Decentralized Control for Enhanced Rotor Angle and Voltage Stability of Large-Scale Power Systems

Several hierarchical centralized control schemes for either rotor angle or voltage stability improvement have been proposed in the literature. They all rely on exchanging information between different subsystems of a large-scale power system. By contrast, in this paper, we propose a hierarchical decentralized control scheme to enhance a unified manner rotor angle and voltage stability while using metered values collected within each subsystem, without any exchange of information between subsystems. Specifically, weakly coupled coherent areas of a power system are first determined. Then, secondary control agents are implemented in each of them to detect and damp rotor angle and voltage instabilities using local synchrophasor measurements. Decentralized control laws based on Lyapunov theory are implemented on FACTS devices for achieving global rotor angle asymptotic stability. Finally, a tertiary voltage control agent provides reference settings to the secondary voltage agents and takes control actions in case the latter fail to damp voltage instabilities. We show that the proposed scheme minimizes the communication bandwidth requirement while exhibiting a system-wide situational awareness. Simulations carried out on the IEEE 118-bus system demonstrate the effectiveness of the proposed hierarchical decentralized control method.

Impact of grid‐tied large‐scale photovoltaic system on dynamic voltage stability of electric power grids

Perfect power system voltage stability is not possible in practice. Generally, the power grid is continually exposed to changes in its load and operating conditions. Therefore, dynamic stability analysis is one the most important and effective elements for greater security, stability and reliability of planning, design, operation and economic aspects of electric power networks. This study investigates and reports on the dynamic stability of the power system with a large-scale photovoltaic system (L-S PV). Two different scenarios with centralised PV power plants are considered in the medium voltage level without voltage regulation capabilities. Simulation results with these scenarios will show how the voltage instability decreases with the L-S PV based on the bus status, disturbance location, and disturbance duration. In addition, the study discusses network terminal voltage, generator's rotor angle, generator's terminal current, generator's reactive power and electrical power output. This study is an extension of the earlier published conference paper.

Transient Stability Enhancement by Optimal Location and Tuning of STATCOM using Biogeography based Optimization Technique

In this paper, transient stability of a multi machine system is evaluated when the system is experienced a three phase fault and the stability of multi machine system is recovered via optimal placement and tuning of STATCOM. Here, the parameters of the STATCOM are tuned by Biogeography based optimization and the STATCOM is positioned optimally in the system. The performance of the tuned system is compared with various operational conditions like without STATCOM, with STATCOM (untuned) and with two STATCOM (untuned). The time domain simulations and the analysis of the multi machine system are done by PSAT (Power System Analysis Toolbox). When the multi machine system is subjected to a three phase fault, voltage stability of the system is collapsed. The multi machine system with STATCOM (tuned by Biogeography based optimization) regains the stability and gives better voltage profile than the system with STATCOM (untuned), with two STATCOM (untuned) and the system without STATCOM. The results are evaluated with the other operational conditions of the system and it proves that the system has the transient stability when the STATCOM (tuned by Biogeography based optimization) is applied.

Optimal wind power generation investment, considering voltage stability of power systems

Studies show that improper sizing and placement of wind farms (WFs) lead to undesired investment and operation costs as well as the risk of voltage instability. Thus, optimal placement of WFs and enough loading margin (LM) are important factors which ensure the voltage stability of system as well as optimal investment and expenditure for WFs development. In this paper, modal analysis is used to determine the optimal place of WFs from the voltage stability viewpoint. Moreover, a new voltage stability constrained wind energy planning (VSC-WEP) model is proposed to determine the optimal yearly wind power penetration while satisfying voltage stability constraints. A 10-years horizon is considered and the net profit from the energy procurement via the WFs' installed optimally, is maximized. Furthermore, the added capacity of WFs and the net profit are analyzed by sensitivity analyzes to investigate the impact of various technical and financial factors on the obtained results. The proposed VSC-WEP model is implemented on the IEEE New-England 39-bus test system, and solved by General Algebraic Modeling System (GAMS) optimization package. The simulation results demonstrate the capability of the proposed model for optimal determination of WFs capacity while preserving a proper LM of system.

Optimal distributed generation planning in active distribution networks considering integration of energy storage

A two-stage optimization method is proposed for optimal distributed generation (DG) planning considering the integration of energy storage in this paper. The first stage determines the installation locations and the initial capacity of DGs using the well-known loss sensitivity factor (LSF) approach, and the second stage identifies the optimal installation capacities of DGs to maximize the investment benefits and system voltage stability and to minimize line losses. In the second stage, the multi-objective ant lion optimizer (MOALO) is first applied to obtain the Pareto-optimal solutions, and then the ‘best’ compromise solution is identified by calculating the priority memberships of each solution via grey relation projection (GRP) method, while finally, in order to address the uncertain outputs of DGs, energy storage devices are installed whose maximum outputs are determined with the use of chance-constrained programming. The test results on the PG&E 69-bus distribution system demonstrate that the proposed method is superior to other current state-of-the-art approaches, and that the integration of energy storage makes the DGs operate at their pre-designed rated capacities with the probability of at least 60%.

Multi-objective distributed wind generation planning in an unbalanced distribution system

In addition to increasing penetration of distributed generation (DG), the distribution system power flow may be significantly impacted by direction and magnitude. This paper proposes a method for optimal placement of wind DG considering the unbalanced operation of distribution systems. The objective function includes static voltage stability index, three-phase unbalance index, system reliability index, and DG investment cost. The untransposed distribution lines and unbalanced load are modelled, and corresponding static voltage stability index and system reliability considering DG penetrations are derived. The expected and stochastic daily distributed generation and demand profiles in four seasons are calculated to improve the accuracy. To solve this multi-objective optimization model, a fuzzy membership function is used to integrate the four individual objectives, and a sensitivity-based method is proposed to solve the model efficiently. Case study on IEEE 13-bus distribution 3-phase networks and 123-node test feeder successfully verifies the performance of the proposed approach.

Coordinated voltage control of wind-penetrated power systems via state feedback control

This paper presents an optimal coordinated voltage control scheme for preserving long-term voltage stability of power systems. Linear quadratic integral (LQI) controller is employed to construct this scheme. Also, this paper considers the detailed dynamic model of doubly-fed induction generator (DFIG) wind turbine, synchronous generators, over excitation limiter (OEL) and under-load tap changer (ULTC) system, which are important elements influencing voltage stability of power systems. The proposed approach at each time instance involves following two major steps: First, the power system nonlinear equations are linearized and optimal controllers are obtained by LQI technique. Then, in the second step the system dynamic behavior is investigated via time-domain simulations by applying the attained optimal control signals at the first step. The impact of the proposed coordinated voltage control scheme is evaluated by time domain simulations on a well-known test system, under variable wind speed and fault conditions.

The Modeling of SVC for the Voltage Control in Power System

One of the major causes of voltage instability in power system is the reactive power limit. Therefore, this paper aims to analyze the effect of Static Var Compensator (SVC) on voltage stability of a power system. There are many ways to control the voltage, but in this paper only focus on the SVC and IEEE-9 buses. The SVC circuit and IEEE-9 buses were designed and modelled in Power World. The Newton Raphson method was applied to compute the load flow solution. Then, the reactive power (Q) was injected to SVC and the effect of SVC on IEEE 9-buses were studied. The analysis of voltage control was considered the conditions of fault occurred at the bus. The simulation results obtained in Power World demonstrate that the improvement voltage in the IEEE 9-buses when the Q was injected into SVC circuit. Besides, the QV curve was plotted to show the sensitivity and variation bus voltages with respect to the Q injection.