An educational software package for Thyristor Switched Reactive Power Compensators using Matlab/Simulink

In this paper, an educational software package called TSCOM (Thyristor Switched Reactive Power Compensators) has been developed. The TSCOM software package contains simulation models of Thyristor Switched Capacitor (TSC) and Thyristor Switched Reactor (TSR)-based Static VAr Compensator (SVC) which are two of the shunt Flexible AC Transmission Systems (FACTS) devices. The design and simulations of TSC and TSR-based SVC are proposed using the Matlab/Simulink 7.04® and SimPowerSystems. The TSC and TSR-based SVC devices are demonstrated at two bus, three bus, infinite-bus, single-phase, three-phase, static load, dynamic load and stair-case load conditions. The effects of TSC and TSR-based SVC devices on load voltage are also analyzed. Student feedback indicates that this package is user-friendly and considerably effective for students and researchers to study theory of switched compensators, the reactive power control and voltage regulation. The proposed package will help to design the practical prototypes for students and researchers.     

Statistical analysis based reactive power optimization using improved differential evolutionary algorithm

This study presents a novel improved differential evolutionary (IDE) algorithm for optimizing reactive power management (RPM) problems. The effectiveness of IDE algorithm is tested on different unimodal and multimodal benchmark functions. The objective function of the RPM is considered as the minimization of active power losses. Initially, the power flow analysis approach is employed to detect the optimal position of flexible AC transmission system (FACTS) devices. The proposed method is used to determine the optimal value of control variables such as generator's reactive power generation, transformer tap settings, and reactive power sources. Furthermore, the efficacy of the IDE approach is compared with other promising optimization methods such as variants of differential evolution algorithm, moth flame optimization (MFO), brainstorm-based optimization algorithm (BSOA), and particle swarm optimization (PSO) on various IEEE standard test bus (i.e., IEEE-30, -57, -118, and -300) systems with active and reactive loading incorporating FACTS devices. A Static VAR compensator (SVC) for shunt compensation and a thyristor-controlled series compensator (TCSC) for series compensation were used as FACTS devices. The proposed IDE method significantly reduces the active power loss, that is, 55.65% in IEEE 30, 39.68% in IEEE 57, 16.32% in IEEE 118, and 8.56% in IEEE 300 bus system at nominal loading. Finally, the statistical analysis such as Wilcoxon signed-rank test (WSRT) and ANOVA test were thoroughly analysed to demonstrate the firmness and accuracy of the proposed technique.     

A computing method-based rearrangement of network protocols to improvise quality factors of FACTS devices and sensors using Newton-Raphson technique

The load flow analysis project was carried out using the Newton-Raphson's iteration technique and a multiobjective method was suggested to minimize power loss, increase bus voltage, reduce operating costs, and controlling the flexible AC transmission system (FACTS) controllers. The key focus is to improvise the load sustainability subjected to controlling of system safety, integrity, and stability margins within specified limits by acquiring optimum place, installation expenses for FACTS controllers. It is important to analyze the benefits and architect the FACTS devices for the power steady state analysis. For effective modeling, the five bus standard is analyzed without the FACTS end devices and with the FACTS controllers. Transient voltage is critical which requires accurate and quick response to avoid the voltage collapse and instability issues. The Newton-Raphson's method of load flow analysis is an iterative method which approximates the set of nonlinear simultaneous load flow equations to a set of linear simultaneous load flow equations using Taylor's series expansion and the terms are limited to first order approximation. The variations in voltage are within 5% for a well designated power system. If it exceeds the specified limit then the performance of equipment will be poor and the life of equipment will reduce. Hence the voltage control is very important to improvise the quality factor of the FACTS controllers and devices in power system. The voltage variations in a bus or node are related to reactive power. If the reactive power is injected to a bus is less than reactive power drawn from the FACTS devices, the voltage instability becomes infinite issue causes damage to the controllers and devices. In a load flow problem, two quantities are specified for each bus and the remaining quantities are obtained by the load flow equation analysis using Newton-Raphson method. This method has been tested for IEEE 30 bus system and then the values are compared and analyzed with MATLAB.     

基于TSC的异步风力发电机风电场的无功功率补偿

为解决风电场并网运行存在的电压质量问题,提出了在风电场并网点进行电容器的分组投切控制方法。本文对风电场安装快速投切电容器组的容量及投切规则进行了研究。提出了计及风速变化对风电场输出有功和无功功率影响的电容器总容量计算方法及控制规则。应用PSCAD/EMTDC软件对某风电场进行了无功补偿优化仿真,结果表明：无功补偿的总容量和分组容量计算准确,可使风电场母线电压保持在允许范围内运行,并且电容器动作次数较少,保证了风电场并网运行时的电压质量。     

计及电压质量的风电场无功主动控制策略研究

随着风力发电的快速发展,电网中风电场并网的数量及规模越来越大,但风电场功率的波动特性会给电网的电压质量及无功控制造成很大的不利影响。为保证风电并网后的电压质量在合格范围内,在对风电机组有功出力特性及无功调节特性分析的基础上,提出了一种新的风电场无功主动分层控制策略。第一层根据负荷预测和风电功率预测获得下一时段的无功功率调整量,第二层则将风电场群需要承担的无功调整量分摊给各个风电机组,通过风电场无功控制实例的仿真对比分析对该无功控制策略的优越性进行了验证。     

Modeling a mixed-integer-binary small-population evolutionary particle swarm algorithm for solving the optimal power flow problem in electric power systems

This research discusses the application of a mixed-integer-binary small-population-based evolutionary particle swarm optimization to the problem of optimal power flow, where the optimization problem has been formulated taking into account four decision variables simultaneously: active power (continuous), voltage generator (continuous), tap position on transformers (integer) and shunt devices (binary). The constraint handling technique used in the algorithm is based on a strategy to generate and keep the decision variables in feasible space through the heuristic operators. The heuristic operators are applied in the active power stage and the reactive power stage sequentially. Firstly, the heuristic operator for the power balance is computed in order to maintain the power balance constraint through a re-dispatch of the thermal units. Secondly, the heuristic operators for the limit of active power flows and the bus voltage constraint at each generator bus are executed through the sensitivity factors. The advantage of our approach is that the algorithm focuses the search of the decision variables on the feasible solution space, obtaining a better cost in the objective function. Such operators not only improve the quality of the final solutions but also significantly improve the convergence of the search process. The methodology is verified in several electric power systems.     

Performance Improvement of Various Types of Induction-based Wind Farms Using Center-node Unified Power Flow Controller

In this paper, we propose the use of center-node unified power flow controller (C-UPFC) for improving the performance of different types of wind farms and mitigating their negative impacts on the grid. C-UPFC is considered one of the modernist members on Flexible AC Transmission System (FACTS). C-stocktickerUPFC has the ability to control several system parameters; the active and reactive power at both ends of the interconnected transmission line and the voltage at the midpoint. Three different induction-based wind farms are considered; 1) Squirrel Cage Induction Generator (SCIG), 2) Doubly Fed Induction Generator (DFIG), and 3) a combination of SCIG and DFIG turbines, i.e., Combined Wind Farm (CWF). C-stocktickerUPFC is comprehensively modelled for the first time in MATLAB Simulink, then the performance of the three wind farms is assessed with and without this device during three phase faults. Probabilistic voltage stability index (Probabilistic VSI) is used to measure the stability of the studied systems. In addition, the performance of three wind farms integrated with C-UPFC is compared with their performance when they integrated with Static synchronous compensators (STATCOM). The results show that C-UPFC has the ability to enhance the performance of wind farms during the three phase fault. C-UPFC is capable to remain the connection between SCIG wind farm and the interconnected grid during the fault. The voltage of CWF is greatly enhanced in the case of using C-UPFC. C-UPFC also improves the output powers of DFIG and CWF, especially after fault clearance.     

基于双PWM变换器的开关磁阻风力发电系统研究

为实现开关磁阻（SRG）风力发电系统中能量在电网与电机之间的双向流动,提出T一种基于双脉宽调制（PWM）变换器的控制方案。机侧变换器进行矢量控制,调节定子有功、无功功率;网侧变换器控制直流母线电压的稳定,调爷网侧功率因数。分析了双PWM变换器的数学模型,并在其d—q轴数学模型的基础上研究r网侧变换器的控制策略,讨论了通过电网电压定向矢量控制实现交流侧功率因数和直流母线电压控制的方法,并利用空间矢量调制方式（SVPWM）对网侧变换器进行控制。基于E述方案建立了SRG系统仿真模型,仿真结果表明,基于电网电压定向的双PWM变换器矢量控制策略能使SRG系统得到快速动态响应并实现高功率因数输出,从而满足变速恒频（VSCF）发电系统的要求。     

基于ETAP的海上风电场接入对电能质量的评估分析

由于海上风资源的多变性,以及风力发电机中存在较多的电力电子元器件,海上风电场并网后会产生电能质量问题。本文选取某海上风电场作为研究对象,基于风电场实际运行数据,参考国标规定,对该风电场的电能质量（电压偏差、电压闪变、电压波动、谐波）进行求解。基于风机的无功特性,本文对某海上风电场接入电网公用变电站的无功补偿容量进行研究。在电能质量计算与分析方面,参考相关规程规定,完成电压偏差、电压闪变、电压波动部分指标的限值与实际值计算,并进行对比;通过ETAP软件中的谐波分析模块,进行谐波模拟仿真,得到谐波指标的实际值,并与理论计算的限值对比。当谐波电流超出国家标准的时候,通过在母线接入单调谐滤波器的方法,进行谐波治理,达到电能质量相关要求。     

Commentary of “Chaotic Krill Herd algorithm for optimal reactive power dispatch considering FACTS devices” by Aparajita Mukherjee et al. “Applied Soft Computing” 44 (2016) 163–190

This short communication presents a discussion of “Chaotic Krill Herd algorithm for optimal reactive power dispatch considering FACTS devices” by Aparajita Mukherjee et al. “Applied Soft Computing” 44 (2016) 163–190. In this paper, an experiment on the reactive power dispatches considering FACTS devices is presented with three example systems, namely 30, 57 and 118-bus test systems. In the reported results for the 57 and 118-bus test system, total losses of load flow with input voltage generators, transformers tab, and capacitor banks were different. In this regard, a clarification on calculations of loss is presented.     

HIERARCHAL CONTROL SYSTEM FOR A VARIABLE SPEED CAGE MACHINE WIND GENERATION UNIT USING NEURAL NETWORKS

A hierarchal control strategy, that addresses three control objectives for a wind generation system, is proposed in this paper. It controls the local bus voltage (to avoid voltage rise), captures the maximum power in the wind and also minimizes the power loss in the induction generator. In the first level, given the instantaneous wind speed, electrical torque and output power, the designed neural networks calculate the desired rotor speed, air‐gap flux and the grid side reactive power. In the second level, the desired current wave shapes (instantaneous three‐phase currents) of the rectifier and the inverter in a double‐sided PWM converter system are calculated. In the third level, the PWM controller guides the system towards the optimum operating conditions. Simulation results show that even as the wind speed changes randomly, the proposed control strategy leads the system to the optimum operating conditions.     

Loadability margin calculation of power system with SVC using artificial neural network

Voltage stability has become a major concern among the utilities over the past decade. With the development of FACTS devices, there is a growing interest in using these devices to improve the stability. In this paper a method using parallel self-organizing hierarchical neural network (PSHNN) is proposed to estimate the loadability margin of the power system with static var compensator (SVC). Limits on reactive generations are considered. Real and reactive power injections along with firing angle of SVC and bus voltage at which SVC is connected, are taken as input features. To improve the performance of network, K-means clustering is employed to form the clusters of patterns having similar loadability margin. To reduce the number of input features in each cluster, system entropy information gain method is used and only those real and reactive power injections, which affect the loadability margin most, are selected. Separate PSHNN is trained for each cluster. The proposed method is implemented on IEEE-30 bus and IEEE-118 bus system. Once trained, the network produces the output, with accuracy and speed. The computation time is also independent of the system size and the load pattern.     

不平衡电网电压下双馈风力发电系统强励控制

针对电网电压不平衡造成的双馈风力发电机(DFIG)定子有功和无功功率振荡、电磁转矩脉动、定、转子电流不平衡等问题,提出了一种双馈风力发电系统转子侧变换器强励控制方案。推导了不平衡电网电压下DFIG定子有功、无功功率的二次谐波分量在同步旋转坐标系中的表达式,并以此为依据设计了电压强励补偿环。分析了有功、无功功率,电磁转矩及定、转子电流二次谐波分量之间的关系,采用单一强励补偿控制器对不同控制目标进行切换强励控制。对1.5MWDFIG系统的控制特性研究验证了所提控制策略的可行性和优越性。     

Direct Power Control of Dfig by Using Nonlinear Model Predictive Controller

This paper proposes a nonlinear model predictive direct power control (PDPC) strategy for a double fed induction generator (DFIG)‐based wind energy generation system. Active and reactive power variations of DFIG are calculated based on machine rules, and a nonlinear model of DFIG is given. A nonlinear model predictive controller (NMPC) is presented based on the useful cost function and constraint that it results in more proximity between simulations and reality. The power and current ripples are reduced and the optimal rotor voltage is generated based on an objective function and the constraints. The rotor voltage vector is calculated in the synchronous reference frame and transferred into the rotor reference frame. Simulation results of a 2 MW DFIG system show good performance of the proposed method during variation of active and reactive powers, machine parameters, and wind speed. Also, the transient responses of active and reactive powers are within a few milliseconds.     

Chaotic krill herd algorithm for optimal reactive power dispatch considering FACTS devices

Conventionally, optimal reactive power dispatch (ORPD) is described as the minimization of active power transmission losses and/or total voltage deviation by controlling a number of control variables while satisfying certain equality and inequality constraints. This article presents a newly developed meta-heuristic approach, chaotic krill herd algorithm (CKHA), for the solution of the ORPD problem of power system incorporating flexible AC transmission systems (FACTS) devices. The proposed CKHA is implemented and its performance is tested, successfully, on standard IEEE 30-bus test power system. The considered power system models are equipped with two types of FACTS controllers (namely, thyristor controlled series capacitor and thyristor controlled phase shifter). Simulation results indicate that the proposed approach yields superior solution over other popular methods surfaced in the recent state-of-the-art literature including chaos embedded few newly developed optimization techniques. The obtained results indicate the effectiveness for the solution of ORPD problem of power system considering FACTS devices. Finally, simulation is extended to some large-scale power system models like IEEE 57-bus and IEEE 118-bus test power systems for the same objectives to emphasis on the scalability of the proposed CKHA technique. The scalability, the robustness and the superiority of the proposed CKHA are established in this paper.     

基于电力电子开关实现的新型用户端混合性无功补偿技术

柔性交流输电系统（FACTS）技术的出现,为提高电网的可控性与可靠性提供了更新更有效的方法,已经成为近年来电力系统所研究的前沿课题之一。静止无功补偿器（SVC）和可控串联补偿器（TCSC）做为FACTS装置中应用最广泛的重要组成成员,是提高电力系统稳定性最有效的工具。因此,研究SVC与TCSC在电力系统中的应用具有非常重要的理论意义和实用价值。本文研究TCSC、SVC的特性,推导出它们的参数模型。通过Matlab软件,建立了SVC与TCSC两种FACTS装置的仿真模型。TCSC为串联补偿装置,通过连续改变其等效阻抗,从而改变输电线路上的串补程度;SVC为并联补偿装置,改善系统的功率因数。通过改变晶闸管的触发角,对晶闸管进行控制。     

基于SVG的风电场接入局域电网的电压稳定性分析

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。     

直驱式风电机组并网动态性能研究

提出发电机侧整流器采用直接电流控制方式,用以稳定直流侧电压、使发电机侧高功率因数运行,减小发电机损耗;电网侧逆变器对有功、无功功率解耦控制,使风机运行在最大功率点,保证系统以单位功率因数并网,减少并网电流谐波,提高并网电能质量。与传统的控制方式相比,该控制方式具有控制结构简单,发电机侧功率因数高,动态响应快等优点。     

新型双馈风力发电机有功功率平滑控制策略研究

针对由于风能的不确定性、风力发电机的大惯性以及风力发电系统的响应延迟性等造成的风力发电机输出有功功率在一定范围内有波动的问题,提出了一种新型双馈风力发电机有功功率平滑控制策略。该控制策略在全风速范围内采用变浆与变速协调控制策略,并在其基础上增加了一个有功功率误差控制环节,将转子电压辅助控制指令值作为反馈量加入原来的转子电压控制指令值,通过控制SPWM脉冲发生器来实现风力发电机定子输出有功功率的平滑控制。Matlab/Simulink仿真结果表明,与传统有功功率控制策略相比,该新型有功功率平滑控制策略有效抑制了双馈风力发电机输出有功功率的波动。     

Voltage stability evaluation of power system with FACTS devices using fuzzy neural network

Voltage stability has been a major concern for power system utilities because of several events of voltage collapses in the recent past. With the developments of flexible ac transmission system (FACTS) devices, power system performance has improved. This paper proposes an approach based on fuzzy neural network to calculate loadability margin of the power system with static synchronous compensator (STATCOM). A multi-input, single output fuzzy neural network is developed. Kohonen self-organizing map is employed to cluster the real and reactive loads at all the buses to reduce the input features, thus limiting the size of the network and reducing computational burden. Uncertainties of real and reactive loads, real and reactive generations, bus voltages and STATCOM parameters are taken into account by transforming them into fuzzy domains using combination of different nonlinear membership functions. A three-layered feed-forward neural network with fuzzy input variables is developed to evaluate the loadability margin. All ac limits are considered. The proposed methodology is applied to IEEE-30 bus and IEEE-118 bus systems. The proposed methodology is fast and accurate as compared to the conventional techniques. This method can also be used for online calculation of the voltage stability of the large power systems.