阻尼振荡的GNF统一潮流控制器设计

在现代电力系统中,统一潮流控制器(UPFC)是调节电压和潮流的有效手段。该文提出一种用遗传算法优化参数的基于径向函数单一神经元的神经网络(RBFNN)和TS模糊控制策略综合而成的统一潮流控制器设计方案,TS模糊控制策略应用非线性规则设计了更为有效的控制器,使用RBFNN避免了产生控制器的训练样本,同时利用GA全局优化TS模糊控制的参数,从而提高系统的暂态稳定性。经验证,该方案比传统的PI控制策略具有更好的系统振荡阻尼性能。     

统一潮流控制器的GNF控制策略设计

统一潮流控制器UPFC(Unified Power Flow Controller)是现代电力系统中调节电压和潮流的有效手段。提出了一种由径向基函数神经网络RBFNN(Radial Basic Function Neuro-Network)和TS(Takagi-Sugeno)模糊控制策略综合而成的统一潮流控制器控制策略设计方案,即遗传神经模糊综合控制GNF(Genetic Neural Fuzzy)。利用TS模糊控制策略实时更新RBFNN参数,同时采用多机系统中的转速信号ITAE指数作为适应度函数。利用遗传算法GA(Genetic Algorithm)优化TS模糊控制策略系数以及辅助阻尼信号参数．提高了系统的暂态稳定性。经验证,该方案比传统的PI控制策略具有更好的系统振荡阻尼性能,改善了系统的动态品质。     

利用多端统一潮流控制器阻尼多模态振荡

研究了多机系统中使用统一潮流控制器(UPFC)抑制电力系统多模态振荡的可行性.首先推导了作为UPFC概念延伸的多端统一潮流控制器(MUPFC)的非线性动态模型和线性化的Phillips-Heffron模型.利用UPFC和MUPFC具有多个控制回路的特点,提出在其多个控制回路上附加多个阻尼控制器来阻尼多模态振荡.通过模态分析,采用可控性指标对系统中的各个弱阻尼模态选取有效的控制回路,并设计了附加阻尼控制器.仿真结果表明,通过该方法确定的在一个UPFC或MUPFC上设置的多个附加阻尼控制器能够成功实现对电力系统多模态振荡的抑制.     

Power system damping enhancement using unified power flow controller (UPFC)

The Unified Power Flow Controller (UPFC) can inject voltage with controllable magnitude and phase angle in series with a transmission line. It can also generate or absorb controllable reactive power. UPFC is expected to be able to damp power system oscillations more effectively than power electronics devices such as SVG and TCSC. In this paper, a control system design of a UPFC for power system damping enhancement based on the eigenvalue control method is proposed. It is made clear that the best design method for the power system damping enhancement is to determine steady‐state values of the UPFC control variables and the control parameters of the UPFC such as gains and time constants simultaneously, because the controllability of UPFC depends on the steady‐state values of UPFC and the power flow condition. The effectiveness of the proposed control system taking into account UPFC inverter ratings is verified by digital time simulation. Furthermore the effects of the input signals to the UPFC controller on small‐signal stability and transient stability enhancement are studied, and it is made clear that UPFC controllers using global information are more effective for power system damping enhancement than those using local information because global information has stronger observability for power system oscillations than local information. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 35–47, 2000     

Comparison of different robust control methods in design of decentralized UPFC controllers

The unified power flow controller (UPFC) integrates properties of both shunt and series compensations, and can effectively alter power system parameters in such a way that increases power transfer capability and enhances system stability. In practice, simple proportional–integral (PI) controllers are used to control the UPFC. However, the PI control parameters are usually tuned based on classical or trial-and-error approaches and as such, they are incapable of obtaining good dynamic performance for a wide range of operating conditions and various loads in power systems. Hence, in this article robust control approaches are proposed based on the quantitative feedback theory (QFT), H_∞ loop-shaping and μ-synthesis, to design UPFC controllers (power-flow and DC-voltage regulator). The three mentioned methods are compared with each other and a supplementary damping controller is developed to improve damping power system oscillations. Here, a single-machine infinite-bus (SMIB) power system, installed with a UPFC (with system parametric uncertainties) is considered as a case study. The system parametric uncertainties are obtained following 40% simultaneous alterations in parameters and load from their typical values. The simulation results indicate satisfactory verifications of the robust control methods in dealing with the uncertainties considered. When the above three methods and the PI controller are compared in performance in several time-domain simulation tests, the results show clear superiority of the three methods over the PI controller, with the QFT presenting the best performance amongst the three robust control.     

Application of adaptive Lyapunov-based UPFC supplementary controller by neural network algorithm in multi-machine power system

In this paper, a new adaptive unified power flow controller (UPFC) based on the Lyapunov method and neural network structure is presented. The corresponding energy function is derived for the single machine infinitive bus system with classic generator model representation. Damping control strategy to improve transient behavior of the system is determined by considering the dynamic modeling of the UPFC. The Lyapunov-based controller is extended to interconnected power system by considering the two-machine equivalent model and the center of inertia concept. The recurrent neural network (RNN) with back propagation algorithm is also used to overcome the uncertainty issues and also to consider the more detailed power system. The designed Lyapunov-RNN-based controller is applied to the interconnected power system between the Esfahan–Yazd region transmission network in Iran power system. The performance of the proposed controller is compared with other different controllers by applying some disturbances in the system. Finally, simulation results are presented and the effectiveness of the proposed method for power system stability enhancement is discussed as well.     

Design of an ANN tuned adaptive UPFC supplementary damping controller for power system dynamic performance enhancement

A supplementary damping controller for a unified power flow controller (UPFC) is designed for power system dynamic performance enhancement. To maintain a good damping characteristic over a wide range of operating conditions, the gains of the UPFC supplementary damping controller are adapted in real time, based on online measured transmission line loadings (active and reactive power flows). To speed up the online gain adaptation process, an artificial neural network is designed. A major feature for the proposed adaptive UPFC supplementary damping controller is that only physically measurable variables (active and reactive power flows over the transmission line) are employed as inputs to the adaptive controller. To demonstrate the effectiveness of the proposed adaptive UPFC supplementary damping controller, computer simulations are performed on a power system subject to a three-phase fault. It is concluded from the simulation results that the proposed adaptive UPFC supplementary damping controller can yield satisfactory dynamic responses over a wide range conditions. The electromechanical mode with an oscillation frequency around 0.78 Hz has been effectively damped by the proposed damping compensators.     

Optimal location and signal selection of UPFC device for damping oscillation

Unified power flow controller (UPFC) is used for controlling the real and reactive power in transmission line and bus voltage simultaneously and independently. An additional task of UPFC is to increase transmission capacity as result of power oscillation damping. The effectiveness of this controller depends on its optimal location and proper signal selection in the power system network. A residue factor has been proposed to find the optimal location of the UPFC controllers and eigenvalue analyses are used to assess the most appropriate input signals (stabilizing signal) for supplementary damping control of UPFC to damp out the inter-area mode of oscillations. The proposed residue factor is based on the relative participation of the parameters of UPFC controller to the critical mode. A simple approach of computing the residue factor has been proposed, which combines the linearized differential algebraic equation model of the power system and the UPFC output equations. While for signal selection a right-half plane zeros (RHP zeros) and Hankel singular value (HSV) is used as tools to select the most receptive signal to a mode of the inter-area oscillation. The placements of UPFC controllers have been obtained for the base case and for the dynamic critical contingences. The effectiveness of the proposed method of placement and selection of signals are demonstrated on practical network of TNB 25 bus system of south Malaysian network and New England 39 bus system.     

Two separate continually online-trained neurocontrollers for a unified power flow controller

The crucial factor affecting the modern power systems today is load flow control. The Unified Power Flow Controller (UPFC) provides an effective means for controlling the power flow and improving the transient stability in a power network. The UPFC has fast complex dynamics and its conventional control is based on a linearized model of the power system. This paper presents the design of neurocontrollers to provide better damping during transient and dynamic control. Two separate neurocontrollers are used for controlling the UPFC, one neurocontroller for the shunt inverter and the other for the series inverter. Simulation studies carried out in the PSCAD/EMTDC environment is described and results show the successful control of the UPFC and the power system with two neurocontrollers. Performances of the neurocontrollers are compared with the conventional proportional plus integral controllers for system oscillation damping under different operating conditions for large disturbances.     

基于LMI方法的VSC-HVDC多重模型阻尼控制器设计

电压源换流器式高压直流输电(VSC-HVDC)具有快速功率调整特性,结合相应附加小信号阻尼控制策略可以提高系统的低频阻尼能力。基于线性矩阵不等式(LMI)的优化方法为电力系统阻尼控制提供了新的设计途径。文中采用2步LMI优化方法,在建立系统多个运行点小信号模型基础上分别设计单一模型和多重模型运行点阻尼控制器,以改善系统阻尼特性。在PSASP中对3机系统的时域仿真分析表明,基于多重模型的阻尼控制器具有较强的适应性,可在大范围运行条件下向系统提供足够的阻尼。     

抑制区域间低频振荡的UPFC模糊滑模控制器

低频振荡是区域互联电力系统面对的重要问题。从暂态能量的角度对区域间低频振荡进行了分析,并以暂态能量函数下降为目标,分析了统一潮流控制器(UPFC)抑制区域间低频振荡的原理。进而设计了UPFC抑制区域间低频振荡的模糊滑模控制策略。该策略采用区域联络线电气量作为输入信号,构造滑模控制的切换函数,然后通过模糊控制器输出控制信号,改变UPFC串联侧输出电压,抑制低频振荡。该方法兼具滑模控制与模糊控制的优点,经四机两区域系统仿真分析,验证了所提抑制策略的有效性。     

UPFC的外层控制器设计

根据UPFC分层控制设计原理,设计外层控制器为内层控制器提供参考信号,从而完成构建综合考虑内部动态和外部系统影响的UPFC控制体系。首先建立含UPFC的系统模型,并构造了修正能量函数。在此基础上基于控制Lyapunov函数法构造了外层控制器。在四川电网上进行的仿真表明,所提出的外层控制器能够有效改善川渝电网的动态性能,提高暂态稳定性。     

UPFC抑制电力系统低频振荡的参数优化研究

为研究统一潮流控制器(UPFC)用于抑制电力系统低频振荡的效果,采用PID控制策略设计了UPFC,并利用遗传算法(GA)和粒子群算法(PSO)分别对UPFC参数进行了优化。对含UPFC的单机无穷大系统进行仿真,仿真结果显示,UPFC对阻尼电力系统低频振荡起到一定的作用,经过参数优化后系统的暂态变短,相关量的波动降低,且粒子群优化算法用于抑制阻尼电力系统低频振荡的效果优于遗传算法。     

基于Normal Form方法的UPFC多个功能控制器间交互影响分析

统一潮流控制器(UPFC)的重要特点之一就是它具有的多控制功能,包括潮流控制、电压控制和稳定性控制等等。然而时域仿真研究表明统一潮流控制器的多个控制器之间可能存在着较强的交互影响。本文研究了规范型(Normal Form)方法用于分析UPFC控制器间的交互影响问题的可能性,并引入一非线性交互指标定量地指示出控制器间的交互强弱程度。所提方法应用到新英格兰10机39节点系统,并通过时域仿真验证了所提规范型理论分析方法的有效性。     

Control algorithms for control of real and reactive power flows and power oscillation damping using UPFC

This paper investigates the application of multivariable control technique to multi-input multi-output (MIMO) non-linear problem of a power transmission system with UPFC. The main objective is to achieve effective independent control of real and reactive power flows with zero dynamic interactions. Towards achieving the objective, feed-back linearization control (FBLC) scheme is implemented in the laboratory for the control of UPFC. A two-bus power system with UPFC has been built in laboratory and the control implementation has been carried out using DSP TMS320LF2407A. Both power flow control and power oscillation damping issues are addressed. The excellent correlation between simulation and experimental results using a laboratory test system establish the validity of the proposed scheme. Although the power stage of the developed laboratory system is a scaled down model and has limited ratings, the FBLC controller can be used equally effectively in a more realistic system set up by appropriate scaling factors for the fed-back signals of currents and voltages and for initiating the inverter voltages. The proposed controller enables UPFC to independently control the real and reactive power with absolute decoupling. Also it is found that the overall performance of the system with the proposed controller is far superior to that using conventional cascade PI control structure.     

统一潮流控制器的多变量控制设计

通过一实例,讨论报告了统一潮流控制器的多个控制器之间存在的交互影响及在负交互影响下,多个控制器设计安排的不合理性。文中建议对统一潮流控制器应设计１个多变量控制器来完成其具有的多个控制功能。并给出了这样１个多变量控制设计的成功实例。     

Stabilizing control of variable impedance power systems: Applications to variable series capacitor systems

In future electric power systems, it will be very important to utilize existing ac networks more effectively with the help of power electronics technology. It has become clear that various types of apparatus utilizing such power electronics technologies as variable series capacitors (VSrC) and high-speed phase shifters (HSPS) can improve transient stability and damping in one-machine, infinite-bus power systems. This paper presents a novel control scheme for variable impedance apparatus such as VSrC and HSPS devices in multi-machine power systems. First, this paper describes a comprehensive approach for control design of VSrC and HSPS apparatus. The proposed control scheme is based on the energy function of multi-machine power systems. The controllers are designed so that the time derivative of the energy function has a smaller negative value than that without controllers. In this sense, the present method assures the improvement of first-swing stability and damping. Next, the proposed control scheme is applied to VSrC apparatus. Digital simulations and eigenvalue analysis are conducted for a three-machine loop system and a five-machine radial system to demonstrate the effectiveness of the proposed method. The results make it clear that the proposed controllers for VSrC can significantly improve both the transient stability and the steady-state stability of power systems.     

A Lyapunov theory based UPFC controller for power flow control

Unified power flow controller (UPFC) is the most comprehensive multivariable device among the FACTS controllers. Capability of power flow control is the most important responsibility of UPFC. According to high importance of power flow control in transmission lines, the proper controller should be robust against uncertainty and disturbance and also have suitable settling time. For this purpose, a new controller is designed based on the Lyapunov theory and its stability is also evaluated. The Main goal of this paper is to design a controller which enables a power system to track reference signals precisely and to be robust in the presence of uncertainty of system parameters and disturbances. The performance of the proposed controller is simulated on a two bus test system and compared with a conventional PI controller. The simulation results show the power and accuracy of the proposed controller.     

Power flow model/calculation for power systems with multiple FACTS controllers

This paper presents a new procedure for steady state power flow calculation of power systems with multiple flexible AC transmission system (FACTS) controllers. The focus of this paper is to show how the conventional power flow calculation method can systematically be modified to include multiple FACTS controllers. Newton–Raphson method of iterative solution is used for power flow equations in polar coordinate. The impacts of FACTS controllers on power flow is accommodated by adding new entries and modifying some existing entries in the linearized Jacobian equation of the same system with no FACTS controllers. Three major FACTS controllers (STATic synchronous COMpensator (STATCOM), static synchronous series compensator (SSSC), and unified power flow controller (UPFC)) are studied in this paper. STATCOM is modeled in voltage control mode. SSSC controls the active power of the link to which it is connected. The UPFC controls the active and the reactive power flow of the link while maintaining a constant voltage at one of the buses. The modeling approach presented in this paper is tested on the 9-bus western system coordinating council (WSCC) power system and implemented using MATLAB software package. The numerical results show the robust convergence of the presented procedure.     

Application of static var system auxiliary controllers to improve the transient performance of series compensated long transmission lines

The paper presents a comparative assessment of the static var system (SVS) bus frequency and line reactive power auxiliary controllers for the transient performance enhancement of series compensated long transmission lines. A new controller, namely, the combined reactive power and frequency (CRPF) auxiliary controller, has been developed and incorporated in the static var control system located at the middle of the transmission line. The series compensation is provided at the sending end of the line. The application of the auxiliary controllers considerably enhances the system damping and the unstable system modes are stabilized. A digital computer simulation study has been performed to compare the effectiveness of the auxiliary controllers under disturbance conditions and the superiority of the (CRPF) auxiliary controller has been established over the other auxiliary controllers.