Power System Stability Enhancement Research Articles

Probabilistic Allocation of Thyristor-controlled Phase Shifting Transformer for Transient Stability Enhancement of Electric Power System

ABSTRACTDue to the large number of uncertainties in operation and planning of power system, it is appropriate to analyse the transient stability assessment as a stochastic problem. This paper presents the probabilistic approach to determine the optimal location of thyristor-controlled phase shifting transformer (TCPST) for enhancing the transient stability of power system. TCPSTs are the cost-effective means to ensure reliable and efficient power flow control in overloaded transmission lines. This feature leads to reduction of the rotor angle separation of synchronous generators during disturbance occurrence which improves transient stability of the system. To select the optimal location of the TCPSTs, the analysis of angular separation of rotors of generators is calculated by considering the probabilistic factors. The Western-System-Coordinating-Council (WSCC) 9-bus and Institute of Electrical and Electronics Engineers (IEEE) New-England 39 bus test systems were used to demonstrate the feasibility and applicability of the presented method.

POWER SYSTEM STABILITY ENHANCEMENT USING STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC)

In this study, a static synchronous series compensator (SSSC) is used to investigate the effect of this device in controlling active and reactive power flow in transmission line. The SSSC is series injected voltage source controller, which leads or lags line current by 90°. In this paper, series compensation provided by an SSSC is considered. A systematic procedure for modeling, simulation and optimally tuning the parameters of a SSSC controller in a multi-machine system, for power system stability enhancement is presented. The problem of SSSC controller is formulated as an optimization problem and Real Coded Genetic Algorithm (RCGA) is investigated to search for the optimal SSSC controller parameters. The results obtained from simulations validate the effectiveness of proposed modeling and tuning approach for power system stability improvement.

Mechanism Analysis and Experimental Validation of Employing Superconducting Magnetic Energy Storage to Enhance Power System Stability

This paper investigates the mechanism analysis and the experimental validation of employing superconducting magnetic energy storage (SMES) to enhance power system stability. The models of the SMES device and the single-machine infinite-bus (SMIB) system with SMES are deduced. Based on the model of the SMIB system with SMES, the action mechanism of SMES on a generator is analyzed. The analysis takes the impact of SMES location and the system operating point into consideration, as well. Based on the mechanism analysis, the P-controller and Q-controller are designed utilizing the phase compensation method to improve the damping of the SMIB system. The influence of factors, such as SMES location, transmission system reactance, the dynamic characteristics of SMES and the system operating point, on the damping improvement of SMES, is investigated through root locus analysis. The simulation results of the SMIB test system verify the analysis conclusions and controller design method. The laboratory results of the 150-kJ/100-kW high-temperature SMES (HT-SMES) device validate that the SMES device can effectively enhance the damping, as well as the transient stability of the power system.

Improved synergetic excitation control for transient stability enhancement and voltage regulation of power systems

Abstract This paper proposes decentralized improved synergetic excitation controllers (ISEC) for synchronous generators to enhance transient stability and obtain satisfactory voltage regulation performance of power systems. Each generator is considered as a subsystem, for which an ISEC is designed. According to the control objectives, a manifold, which is a linear combination of the deviation of generator terminal voltage, rotor speed and active power, is chosen for the design of ISEC. Compared with the conventional synergetic excitation controller (CSEC), a parameter adaptation scheme is proposed for updating the controller parameter online in order to improve the transient stability and voltage regulation performance simultaneously under various operating conditions. Case studies are undertaken on a single-machine infinite-bus power system and a two-area four-machine power system, respectively. Simulation results show the ISEC can provide better damping and voltage regulation performance, compared with the CSEC without parameter adaptation scheme and the conventional power system stabilizer.

Coordination of PSS and PID Controller for Power System Stability Enhancement – Overview

In power systems, Low Frequency Oscillations (LFO) in the range of 0.1 - 2.5 Hz have been solved through Power System Stabilizer (PSS). Proportional Integral Derivative (PID) controller is the simplest and effective solution to the most of control engineering applications today. Based on advantage, the PID controller combined with PSS to enhance the stability in power system. In practice most of the PID controller and parameters of PSS are tuned manually and fixed for certain operating conditions. In general power systems are non linear, conventional methods had lack of robustness. Therefore it is necessary to take advantage in simplifying the problem and implementation by utilizing most efficient optimization methods. From this view, many optimization methods and algorithms have been employed to tune the PID gains and PSS parameters. This paper broadly reviews the optimization methods and algorithms such as Conventional methods, Soft Computing, Genetic Algorithm (GA), Evolutionary Programming (EP), Differential Evolution (DE) and Swarm Intelligence methods were available for tuning the PID gains and PSS parameters successfully. Research showed the design of controllers based on conventional methods; soft computing and population based algorithms suffer from limitations. However, swarm intelligence techniques proved to be able to overcome these limitations. Swarm intelligence based coordinated controller (PID+PSS), will effectively enhance the small signal stability and transient stability in power system. An effort is made in this paper to present a broad analysis of tuning the PID gains and PSS parameters by various researchers.

System reliability enhancement in a metropolitan area using HVDC technology

Recently, due to the increase of massed demand areas, in terms of system reliability has been raised several issues such as voltage, frequency problems and fault current. In Korean power systems, more than 40% of the total loads are concentrated in metropolitan areas, however most large plants are located in non-metropolitan areas. In these long-distance transmission systems, the transmission capacity is limited not by thermal capacity constraint, but by stability constraint. To solve these problems, the study of enhancing power system stability and increasing transmission capacity has been progressed. In this paper, we analyse domestic power systems in order to discuss the best solutions for current reduction using PSS/E simulation. Fault current problems can be resolved through gird segmentation which adopts Voltage Sourced Converter Back-to-Back High Voltage Direct Current (VSC BTB HVDC). Furthermore, grid segmentation can enhance the interface flow margin with the independent reactive power control in...

A hybrid particle swarm optimization and bacterial foraging for power system stability enhancement

A novel hybrid approach involving particle swarm optimization (PSO) and bacterial foraging optimization algorithm (BFOA) called bacterial swarm optimization (BSO) is illustrated for designing static var compensator (SVC) in a multimachine power system. In BSO, the search directions of tumble behavior for each bacterium are oriented by the individual's best location and the global best location of PSO. The proposed hybrid algorithm has been extensively compared with the original BFOA algorithm and the PSO algorithm. Simulation results have shown the validity of the proposed BSO in tuning SVC compared with BFOA and PSO. Moreover, the results are presented to demonstrate the effectiveness of the proposed controller to improve the power system stability over a wide range of loading conditions. © 2014 Wiley Periodicals, Inc. Complexity 21: 245–255, 2015

An ultra-capacitor for frequency stability enhancement in small-isolated power systems: Models, simulation and field tests

The most relevant issue in operation of isolated power systems is frequency stability. Frequency stability is concerned with the ability of generators to supply the loads at an acceptable frequency after a disturbance. Frequency stability is governed by the kinetic energy stored in the generator-prime mover rotating masses and the prime mover frequency primary regulation. If frequency excursions are not within +/−2.5Hz range, cascade tripping of the remaining generators can occur because of generator over/under frequency protections tripping. Energy storage systems can contribute to frequency stability enhancement if their discharging is governed by a frequency controller.Endesa is leading a research project on testing the state of the art of energy storage systems for several applications (peak-shaving, voltage control, frequency control) in several isolated power systems of the Canary Islands. Several applications are being investigated. One of them consists on the application of a 4MW–5s ultracapacitor (UC) for frequency stability enhancement of the La Palma power system.This paper reports the dynamic model developed for time domain simulation and controller design of frequency stability, and field tests undertaken to validate models and the controller settings. A simple but still accurate model is presented. The proposed model takes into account the UC’s state of charge (SoC) and it represents the dynamics of the power electronics by means of a non-linear first-order model. The frequency control consists of droop control and inertia emulation. Ramp rate limits, power limits and SoC are also taken into account in the frequency control. In comparison with the recorded field tests, the proposed model is able to accurately represent the response of the UC for the purpose of frequency stability analysis.

Improved Step Response of Power System Stabilizer using Fuzzy Logic Controller

As every power system is constantly being subjected to disturbances, we should see that these disturbances do not make the system unstable. Therefor additional signals derived from speed deviation, excitation deviation and accelerating power are injected into voltage regulators. The device to provide these signals is referred as power system stabilizer. The use of power system stabilizers has become very common in operation of large electric power systems. The conventional PSS which uses lead-lag compensation, where gain settings designed for specific operating conditions, is giving poor performance under different loading conditions. Therefore, it is very difficult to design a stabilizer that could present good performance in all operating points of electric power systems. In an attempt to cover a wide range of operating conditions, Fuzzy logic control has been suggested as a possible solution to overcome this problem. In this paper, a systematic approach to fuzzy logic control design is proposed. The study of fuzzy logic power system stabilizer for stability enhancement of a single machine infinite bus system is presented. In order to accomplish the stability enhancement, speed deviation and acceleration of the rotor synchronous generator are taken as the inputs to the fuzzy logic controller. These variables take significant effects on damping the generator shaft mechanical oscillations. The stabilizing signals were computed using the fuzzy membership function depending on these variables. The performance of the system with fuzzy logic based power system stabilizer is compared with the system having conventional power system stabilizer and system without power system stabilizer

Smart control techniques for design of TCSC and PSS for stability enhancement of dynamical power system

This paper deals with the simultaneous application of thyristor controlled series capacitor based damping controller and power system stabilizer for stability improvement of dynamic power system. The adaptive neuro-fuzzy inference system and Levenberg–Marquardt artificial neural network algorithm are used to develop the control strategy for thyristor controlled series capacitor based damping controller and power system stabilizer. The power system stabilizer generates appropriate supplementary control signal to an excitation system of synchronous generator to damp the frequency oscillations and improves the performance of the power system dynamic. The performance of power system affected due to the system configuration and load variation. In order to achieve the appreciable damping, the series capacitor is suggested in addition to the power system stabilizer. Nonlinear simulations of single machine infinite bus system are carried out using the individual application of power system stabilizer and simultaneous application of power system stabilizer and thyristor controlled series capacitor. The comparison analysis between conventional and smart control strategies based controllers is demonstrated. Single machine infinite bus system is tested under various operating conditions and disturbances to show the effectiveness of proposed control schemes.

Design of power system stabilizers based on μ-controller for power system stability enhancement

The problem of the poorly damped low-frequency (0.1–0.4Hz) oscillations of power systems has been a matter of concern to power engineers for a long time, because they limit the power transfer capability in power systems. The power systems stability is also affected by these poorly damped oscillations and can lead to the system instability. The paper presents a design PSSs based on μ-controller to enhance power systems stability and improve power transfer capability. MATLAB dynamic model was developed for a power system and lead-lag PSS structure is considered in the model. Damping torque technique is applied to tune the PSS parameters. The results of this technique have been verified by eigenvalue analysis and time-domain simulations. The optimal sampling time was determined for transferring the s-domain of PSS model to digital (z-domain) model and then it was implemented on μ-controller chip. The peripheral interface controller (PIC) μ-controller type was used and the developed MATLAB model was interfaced with the μ-controller. The simulations results show that the system time responses under different operating conditions are well damped with the designed PSS. Moreover, the proposed PSS based μ-controller is relatively simple and suitable for real-time applications in the future smart power grid where the stabilizing signals to the PSSs will be provided by wide-area measurement signals using the new technology of synchrophasors.

Application of thyristor-controlled series reactor for fault current limitation and power system stability enhancement

Various types of Fault Current Limiters (FCLs) have been proposed and proven to offer numerous advantages with respect to transmission losses, voltage quality, and power system stability. However, FCL research has largely focused on only the FCL system, including optimization of components, efficiency improvement, and cost reduction. Conventional solutions to fault current problems, such as splitting buses, replacing switch gear, and installing permanently inserted series reactors, are still widely used in the field, but impair overall power system reliability. In this paper, a Thyristor-Controlled Series Reactor (TCSR) is used to limit fault current and enhance power system stability simultaneously. A TCSR controller is designed using an advanced mathematical approach and the impact of TCSR is analyzed from the perspective of voltage security enhancement. The benefits of the proposed TCSR-based FCL in terms of both voltage security and angle stability are demonstrated through bulk power system simulation results. The feasibility of real power system application is also assessed using actual power system data.

A Control Strategy for Transient Stability Improvement of Doubly-Fed Wind Power Generation System

A novel inverter control strategy to enhance the transient stability of grid-connected wind farm based on doubly-fed induction generator (DFIG) is presented. Adding transient angle control strategy in the rotor side converter active control loop, this can dissipate the system unbalancing energy and restrain the system oscillations by the variation of wind turbine speed. Adding transient voltage control strategy in reactive control loop, this can provide fast reactive power compensation and support the restoration and reconstruction of the grid voltage when fault occurred. The control strategy which can improve the transient Angle stability and transient voltage stability at the same time is put forward. Finally, a testing system including a DFIG-based wind farm is realized using DigSILENT/Power Factory, the strategy validation and the contribution to power system stability enhancement are verified by simulation.

Voltage Stability Enhancement in Power System using STATCOM based on Specific Coefficient Algorithm (SCA)

The countries like India with increasing demand of electric power day by day it is difficult to expand the existing transmission system due to difficulties in right of way and cost problem in transmission network expansion. So, we need power flow controllers to increasing transmission capacity and controlling power flows Increased demands on transmission, absence of long-term planning, and the need to provide open access to generating companies and customers, all together have created tendencies toward less security and reduced quality of supply. Due to increase in demand, the transmission system becomes more stressed, which in turn, makes the system more vulnerable to voltage instability. Voltage stability plays an important role in the operation of the power system and there are major concerns about it for better utilizations of the system. Improvement in power system performance can be obtained using flexible AC transmission systems (FACTS). FACTS devices are capable of the simultaneous control of the bus voltage and real and reactive power flow in transmission systems independently; but because of excessive cost, the number and the location of these devices should be indicated optimally. This paper proposes a method of optimization of STATCOM allocation based on specific coefficients algorithm (SCA) to specify the number, location and input values by minimizing the voltage indices of system buses. The proposed SCA noticeably improves the accuracy and performance of traditionally used optimization processes especially in large scale networks. This method is applied to the 14-bus IEEE standard system. The results of ordinary and new optimization algorithm have shown the great improvement in optimization process using SCA.

Design of Anti-Windup Compensator for Energy Storage-Based Damping Controller to Enhance Power System Stability

The application of energy storage (ES) in power system is limited due to the high cost of the ES device, which exponentially increases with its capacity. This paper is to improve the saturation-dependent stability of the power system equipped with the energy storage based damping controller (ESDC), and hence, reduce the required size of the ES. The phenomenon that the capacity of ES is smaller than the required value produced by the ESDC, is modeled as actuator saturation using the saturation function. The proposed method is to design an anti-windup compensator (AWC), which in the event of saturation, produces a signal based on the output difference between the ESDC and saturated ES and then augment the signal to the ESDC to alleviate the adverse effect of saturation. The AWC is designed with the reduced-order model of power system and linear matrix inequality. Detailed design procedure is introduced. Case studies based on a modified 4-machine 2-area power system and 10-machine New England power system are carried out to demonstrate the effectiveness of the AWC design method.

Robust tuning of power system stabilizer for small signal stability enhancement using metaheuristic bat algorithm

Abstract In this paper, the design of a conventional power system stabilizer (CPSS) is carried out using the bat algorithm (BA) to optimize its gain and pole-zero parameters. The proposed optimization of CPSS parameters is considered with an objective function based on eigenvalue shifting to guaranteeing the stability of nonlinear plant for a wide range of operating conditions of the single-machine infinite-bus power system model. The system performance with BA optimized CPSS (BA-CPSS) controller is compared with a particle swarm optimization based CPSS (PSO-CPSS) controller. The robustness is tested by considering several operating conditions (133 in numbers) to establish the superior performance with BACPSS over the PSO-CPSS.

Application of GA for Optimal Location of FACTS Devices for Steady State Voltage Stability Enhancement of Power System

This paper presents a non traditional optimization technique, genetic algorithm to seek the optimal allocation, type and size of FACTS devices to control line flows, to maintain bus voltage to desired level and to minimize system losses. The targeted objectives are maximizing the static security margins and voltage stability while minimizing losses. Congestion management is also done by optimally placing FACTS controllers with line outage. Matlab coding has been developed for the purpose of simulation. Assessments are done on IEEE 30 bus system against different loading conditions with two FACTS devices SVC and TCSC implemented in steady state and the results verify the potency of propound algorithm to find the optimal location for power system stability.

Transient stability enhancement of multimachine power systems using nonlinear observer-based excitation controller

This paper presents an approach to design a nonlinear observer-based excitation controller for multimachine power systems to enhance the transient stability. The controller is designed based on the partial feedback linearization of a nonlinear power system model which transforms the model into a reduced-order linear one with an autonomous dynamical part. Then a linear state feedback stabilizing controller is designed for the reduced-order linear power system model using optimal control theory which enhances the stability of the entire system. The states of the feedback stabilizing controller are obtained from the nonlinear observer and the performance of this observer-based controller is independent of the operating points of power systems. The performance of the proposed observer-based controller is compared to that of an exact feedback linearizing observer-based controller and a partial feedback linearizing controller without observer under different operating conditions.

Analysis and assessment of VSC excitation system for power system stability enhancement

The voltage source converter (VSC) excitation system is a novel excitation system based on pulse-width modulation (PWM) voltage source converter, which is proposed as improved alternatives to the conventional thyristor excitation systems. This paper aims to provide theoretical confirmation of power system stability enhancement by the VSC excitation system. The reactive current injected to generator terminals by the VSC excitation system can be controlled flexibly. Its capability of enhancing power system stability is investigated in this paper. The simplified model of VSC excitation system suitable for use in system stability studies is developed. An extended Philips–Heffron model of a single-machine infinite bus (SMIB) system with VSC excitation system is established and applied to analyze the damping torque contribution of the injected reactive current to the power system. This paper also gives a brief explanation on why the VSC excitation system can enhance the transient stability in light of equal area criterion. The results of calculations and simulations show that the injected reactive current of VSC excitation system contributes to system damping significantly and has a great effect on the transient stability. When compared with conventional thyristor excitation systems, the VSC excitation system can not only improve the small-signal performance of the power system, but also can improve the system transient stability limit.

Optimal Placement of DG Units Considering Power Losses Minimization and Voltage Stability Enhancement in Power System

Nowadays, increasing the numbers of DG units has affected the system parameters like stability and power losses. Controlling these parameters makes the power system operators optimize the placement and penetration level of these sources. Consequently, several methods with various targets have been studied until now. In this paper, the evaluation of placement and penetration level of DG units considering stability improvement and power losses reduction has been investigated. To achieve these goals, different objective functions with several operating constraints were proposed. The well-known NSGA_II was utilized to optimize the objective functions considering the operating constraints. NSGA_II is an evolutionary based multi-objective optimization tools which has great advantages in comparison with other evolutionary algorithms. The utilized method was applied to IEEE 14 -bus and 57 -bus test systems. The ability of the proposed method in enhancing of voltage stability, improvement of voltage profile, and reduction of power losses were confirmed using simulation results.