Hybrid linearization of a power system with FACTS devices for a small signal stability study: Concept and application

This paper deals with a hybrid linearization method of a power system with flexible AC transmission system (FACTS) devices. The linearized power system model provides useful information, which is necessary for the small signal stability study and the controller design. Although the algebraic linearization method provides an accurate and parameterized linear system, it may incur computation burdens for the large power system especially with multiple FACTS devices. The numerical identification of linearized system by utilizing input–output numerical data is highly versatile. However, quite amount of valuable information may be not fully utilized. In this paper, a hybrid method in which the algebraic and the numerical linearization technique are combined is presented. While both the power system and the FACTS devices are separately linearized by using algebraic method, the interaction terms between the power system and FACTS devices are numerically identified by adopting the quadratic optimization technique. The proposed hybrid linearization technique is tested on the WSCC system in which one thyristor-controlled series capacitor is installed. Both eigenvalue analysis and time-domain simulation results verify that the proposed method can effectively identify the linearized model of the power system with FACTS devices.     

含UPFC的灵活交流输电系统最优潮流控制

潮流计算和无功优化计算是电力系统非常重要的计算,两者都包括在电力系统最优潮流（OPF）问题中,灵活交流输电系统（FACTS）的出现需要对传统的潮流计算进行修正,利用遗传算法探讨了含统一潮流控制器（UPFC）的灵活交流输电系统最优潮注控制问题,计算机仿真表明,该方法可有效解决含UPFC的灵活交流输电最优潮流控制。     

Planning of multi-type FACTS devices in restructured power systems with wind generation

Many electrical power systems are changing from a vertically integrated entity to a deregulated, open-market environment. This paper proposes an approach to optimally allocate multi-type flexible AC transmission system (FACTS) devices in restructured power systems with wind generation. The objective of the approach is to maximize the present value of long-term profit. Many factors like load variation, wind generation variation, generator capacity limit, line flow limit, voltage regulation, dispatchable load limits, generation rescheduling cost, load shedding cost, and multilateral power contracts are considered in problem formulation. The proposed method accurately evaluates the annual costs and benefits obtainable by FACTS devices in formulating the large-scale optimization problem under both normal condition and possible contingencies. The overall problem is solved using both Particle Swarm Optimization (PSO) for attaining optimal FACTS devices allocation as main problem and optimal power flow as sub optimization problem. The efficacy of the proposed approach is demonstrated for modified IEEE 14-bus test system and IEEE 118-bus test system.     

Assessment of techno-economic contribution of FACTS devices to power system operation

In contemporary power system studies, the optimal allocation and utilization of Flexible AC Transmission System (FACTS) devices are important issues primarily due to their cost. In this study four types of FACTS devices (Static VAr compensator (SVC), Thyristor-Controlled Series Capacitor (TCSC), Thyristor-Controlled Voltage Regulator (TCVR), and Thyristor-Controlled Phase Shifting Transformer (TCPST)) are optimally placed in a multi-machine power system to reduce the overall costs of power generation. The placement methodology considers simultaneously the cost of generated active and reactive powers and cost of selected FACTS devices for a range of operating conditions. The optimal power flow (OPF) and genetic algorithm (GA) based optimization procedure are employed to solve the allocation task. The net present value (NPV) method is used to assess the economic value of the proposed methodology. In addition to net reduction in generation cost allocated FACTS devices increased power transfer across the network and improved damping of electromechanical oscillations.     

Optimal sizing of SSSC controllers to minimize transmission loss and a novel model of SSSC to study transient response

In this paper, based on steady-state models of flexible AC transmission system (FACTS) devices, the sizing of static synchronous series compensator (SSSC) controllers in transmission network is formed as an optimization problem. The objective of this problem is to reduce the transmission losses in the network. The optimization problem is solved using particle swarm optimization (PSO) technique. The Newton–Raphson load flow algorithm is modified to consider the insertion of the SSSC devices in the network. Numerical examples, illustrating the effectiveness of the proposed algorithm, are introduced. In addition, a novel model of a three-phase voltage source converter (VSC) that is suitable for series connected FACTS a controller is introduced. The model is verified by simulation using Power System Blockset (PSB) and Simulink software.     

Impact of a FACTS controller on reliability of composite power generation and transmission system

This paper proposes an optimization model to use in composite power system reliability evaluation method incorporating the impact of FACTS devices. The conventional dc flow-based linear programming model used in composite system reliability evaluation method is converted into a non-linear optimization model to include the impact of FACTS devices on reliability of power system. The proposed model is tested on 24-bus IEEE-reliability test system (RTS). Annualized reliability indices are calculated using the model and compared with the indices calculated without considering FACTS devices.     

Power system with multi-type FACTS devices states estimation based on predictor–corrector interior point algorithm

This paper addresses a state estimation problem of power systems incorporating various flexible alternating current transmission system (FACTS) devices. Static var compensators, thyristor controlled series compensators, and unified power flow controllers are considered since they represent various kinds of FACTS devices. By considering constraints of system buses and devices, the estimation problem can be formulated as a nonlinear optimization with constraints. An algorithm based on predictor–corrector interior point is applied to solve the problem. The IEEE 14- and 118-bus systems modified by incorporating FACTS devices are used as test systems to verify and demonstrate the effectiveness of the proposed algorithm. Numerical results indicate that the proposed algorithm performs better than the primal dual interior point based method even the presence of bad measurement data.     

Allocation of multi-type FACTS devices using multi-objective genetic algorithm approach for power system reinforcement

This paper presents a novel approach to find optimum locations and capacity of flexible alternating current transmission systems (FACTS) devices in a power system using a multi-objective optimization function. Thyristor controlled series compensator (TCSC) and static var compensator (SVC) are the utilized FACTS devices. Our objectives are: active power loss reduction, new introduced FACTS devices cost reduction, voltage deviation reduction, and increase on the robustness of the security margin against voltage collapse. The operational and controlling constraints, as well as load constraints, are considered in the optimum allocation. A multi-objective genetic algorithm (MOGA) is used to approach the Pareto-optimal front (non-dominated) solutions. In addition, the estimated annual load profile has been utilized in a sequential quadratic programming (SQP) optimization sub-problem to the optimum siting and sizing of FACTS devices. IEEE 14-bus Network is selected to validate the performance and effectiveness of the proposed method.     

含STATCOM的双馈风电场无功协调补偿策略

双馈异步发电机(DFIG)可以参与系统无功功率的调节,但其无功补偿作用有限,为了实现DFIG的恒功率因数模式运行,仍需要多种无功补偿装置(如FACTS装置、固定电容器)间的无功协调补偿。针对无功补偿装置不同的补偿特性,本文提出了一种含STATCOM的无功协调补偿策略,适用于解决风速波动期间STATCOM和固定电容器对无功的协调补偿问题,其根据并网点电压通过闭环反馈灵活整定风电场所需无功参考值,按照与集电母线的电压差将参考值进行不同母线间的分配,并按照磁滞控制策略进行无功补偿装置之间的协调控制。PSCAD/EMTDC下的算例仿真表明,所提无功协调补偿策略在暂稳态情况下均具有良好的补偿效果。     

大型发电机组调速器的非线性最优PSS

提出了一种大型水电站调速系统的非线性最优电力系统稳定器(PSS)的原理和技术.该技术的关键是采用了状态-动态-测量(SDM)的反馈方法.计算机仿真和动模实验证明,利用该方法推导出的水电站调速系统非线性最优PSS(GNOPSS)控制规律能够显著提高远距离输电系统的安全稳定性,其效能价格比远超过多种FACTS设备,且与FACTS设备的效果是叠加的,不发生矛盾.该研究成果同样适用于大型火电机组的汽门开度调节系统.     

基于FACTS的现货市场阻塞解决方法研究

在电力市场环境下,利用柔性交流输电系统FACTS(FlexibleACTransmissionSystem)设备解决网络阻塞问题,获取更大的经济效益已经越来越引起人们的重视。提出基于FACTS的现货市场阻塞解决方法。从安全域的角度分析了引入FACTS控制作用解决阻塞问题的机理,建立了含FACTS控制作用的潮流和最优潮流模型,并用算例进行了分析。研究结果表明,FACTS的控制作用可以有效地解决网络传输阻塞问题,降低购电成本,避免由于网络输电阻塞引起节点电价的震荡。     

State-variable control of shunt FACTS devices using phasor measurements

This paper addresses the problem of state-variable stabilizing control of power system using shunt FACTS devices. This stabilizing control is activated in the transient state of a power system and is supplementary with respect to the main steady-state control of a FACTS device. Stabilizing control laws have been derived for a non-linear multi-machine system model using direct Lyapunov method with the aim to maximize the rate of energy dissipation during power swings and therefore maximization of damping. The proposed control strategy is executed by a non-linear multi-loop controller with rotor angles and speed deviations of synchronous generators used as the input signals. The input signals, obtained from a phasor measurement system, are necessary only from a small area around the controlled shunt FACTS device. Validity of the proposed state-variable control has been confirmed by computer simulation for a small multi-machine test system.     

面向目标的FACTS设备智能预估控制方法(一)

一种新的ＦＡＣＴＳ设备的多目标优化控制方法,即ＦＡＣＴＳ设备的智能预估控制方法综合了预测控制和逆系统控制的优点,将确定ＦＡＣＴＳ设备最优控制信号的过程分解为先对ＦＡＣＴＳ设备的候选输出进行筛选作业,以求得ＦＡＣＴＳ设备的最优输出,然后再根据最优输出反演计算ＦＡＣＴＳ设备的实际控制信号这样两个子过程。在各个子过程中,人工神经网络技术和模糊推理方法被分别用于解决不同的问题。文中还以先进的静止无功发生器     

Optimal location and setting of SVC and TCSC devices using non-dominated sorting particle swarm optimization

In this paper, a new method for optimal locating multi-type FACTS devices in order to optimize multi-objective voltage stability problem is presented. The proposed methodology is based on a new variant of particle swarm optimization (PSO) specialized in multi-objective optimization problem known as non-dominated sorting particle swarm optimization (NSPSO). The crowding distance technique is used to maintain the Pareto front size at the chosen limit, without destroying its characteristics. To aid the decision maker choosing the best compromise solution from the Pareto front, the fuzzy-based mechanism is employed for this task. NSPSO is used to find the optimal location and setting of two types of FACTS namely: Thyristor controlled series compensator (TCSC) and static var compensator (SVC) that maximize static voltage stability margin (SVSM), reduce real power losses (RPL), and load voltage deviation (LVD). The optimization is carried out on two and three objective functions for various FACTS combinations considering. For ensure the robustness of the proposed method and gives a practical sense of our study, N − 1 contingency analysis and the stress of power system is considered in the optimization process. The thermal limits of lines and voltage limits of load buses are considered as the security constraints. The proposed method is validated on IEEE 30-bus and realistic Algerian 114-bus power system. The simulation results are compared with those obtained by particle swarm optimization (PSO) and non-dominated sorting genetic algorithms (NSGA-II). The comparisons show the effectiveness of the proposed NSPSO to solve the multi-objective optimization problem and capture Pareto optimal solutions with satisfactory diversity characteristics.     

Genetic algorithm-based fuzzy multi-objective approach to congestion management using FACTS devices

This paper investigates a novel optimization-based methodology for placement of Flexible AC Transmission Systems (FACTS) devices in order to avoid congestion in the transmission lines while increasing static security margin and voltage profile of a given power system. The optimizations are carried out on the basis of location, size, and number of FACTS devices. Thyristor Controlled Series Compensator (TCSC) and Static Var Compensator (SVC) are two FACTS devices which are implemented in this investigation to achieve the determined objectives. The problem is formulated according to Sequential Quadratic Programming (SQP) problem in the first stage to accurately evaluate static security margin with congestion alleviation constraint in the presence of FACTS devices and estimated annual load profile. In the next stage a Genetic Algorithm (GA)-based fuzzy multi-objective optimization approach is used to find the best trade-off between conflicting objectives. The IEEE 14-bus test system is selected to validate the proposed approach.     

Power flow control approach to power systems with embedded FACTS devices

This paper focuses on developing an approach to steady-state power flow control of flexible AC transmission systems (FACTS) device-equipped power systems. Based on a power-injection model of FACTS devices and an optimal power flow model, a novel versatile power flow control approach is formulated, which is capable of implementing power flow control incorporating any FACTS device flexibly. Different from existing FACTS device control approaches, the active and (or) reactive power injections are taken as independent control variables. Therefore, using this method, Jacobian matrix need not be changed, although various FACTS devices possess different physical models and different control parameters. Furthermore, it enables the integration of FACTS devices into the existing power system analysis and control programs efficiently. Physical limits of the FACTS devices are also considered in the model. Numerical results on a reduced practical system and a 1500-bus practical system with various FACTS devices are presented to illustrate the vigorousness of the proposed approach.     

OPF with SVC and UPFC modeling for longitudinal systems

This paper presents a formulation of the Optimal Power Flow problem with an explicit modeling of Static Var Compensator (SVC) and Unified Power Flow Controller (UPFC) devices. The optimization problem is solved by using Sequential Quadratic Programming, where two convergence criteria and four different methods are studied to solve the quadratic subproblems. The proposed model is integrated in an object-oriented based decision support platform for competitive power markets. Validation of the method and practical applications to real longitudinal systems are discussed, where FACTS location and a UPFC-based interconnection are described. Results show the impact of SVC and UPFC FACTS technologies in the physical and economic behavior of a real system.     

UPFC状态反馈精确线性化潮流控制策略

统一潮流控制器(unified power flow controller,UPFC)传统线性控制器的性能可能因运行点的大范围变化而恶化,针对该问题提出了一种基于微分几何状态反馈精确线性化理论的UPFC非线性潮流控制策略。通过选择李雅普诺夫型输出函数、适当的非线性坐标变换和状态反馈将UPFC的5阶非线性系统完全转化为一个线性系统,然后采用线性极点配置方法设计了UPFC内部潮流控制器。IEEE 118节点系统的仿真对比结果表明,所提UPFC潮流控制策略改进了传统PI控制近似线性化的缺陷,有效适应了UPFC控制范围的大幅度变化,在提高电力系统暂态稳定性方面的效果明显优于传统PI控制。此外,该控制策略设计过程可以应用于所有基于电压源型换流器(voltage source converter,VSC)的柔性交流输电系统(flexibleAC transmission system,FACTS)装置。     

基于极大极小值原理的UPFC控制器设计

统一潮流控制器(UPFC)是一个多功能柔性交流输电系统(FACTS)装置,而电力系统的运行条件经常变化,如何协调设计UPFC的多控制通道并确保电力系统大范围稳定是一个难点。文中以特征值尽可能位于远离虚轴的左半平面为目标函数,将阻尼控制器的参数优化问题转化为一个极大极小值优化问题,并通过一种两种群遗传算法加以求解,以适应电力系统运行条件的大范围变化。与传统的控制器设计方法相比较,文中所提出的方法具有设计简便、智能化程度高、控制器适应性好的优点。以新英格兰测试系统为例,设计了UPFC控制器以抑制系统中可能发生的低频振荡。时域仿真结果表明基于极大极小值原理设计的UPFC控制器能适应宽广运行条件的变化,确保系统的大范围稳定。     

Multi-objective PID controller tuning for a FACTS-based damping stabilizer using Non-dominated Sorting Genetic Algorithm-II

Design of an optimal controller requires optimization of multiple performance measures that are often noncommensurable and competing with each other. Design of such a controller is indeed a multi-objective optimization problem. Non-Dominated Sorting in Genetic Algorithms-II (NSGA-II) is a popular non-domination based genetic algorithm for solving multi-objective optimization problems. This paper investigates the application of NSGA-II technique for the tuning of a Proportional Integral Derivate (PID) controller for a Flexible AC Transmission System (FACTS)-based stabilizer. The design objective is to improve the damping of power system when subjected to a disturbance with minimum control effort. The proposed technique is applied to generate Pareto set of global optimal solutions to the given multi-objective optimization problem. Further, a fuzzy-based membership value assignment method is employed to choose the best compromise solution from the obtained Pareto solution set. Simulation results are presented and compared with a conventionally designed PID controller under various loading conditions and disturbances to show the effectiveness and robustness of the proposed approach. Finally, the proposed design approach is extended to a multi-machine power system to damp the modal oscillations with minimum control efforts.