Free‐weighting matrices‐based robust wide‐area FACTS control design with considering signal time delay for stability enhancement of power systems

This paper presents a free‐weighting matrix (FWM) method based on linear control design approach for the wide‐area robust damping (WARD) controller associated with flexible AC transmission system (FACTS) device to improve the dynamical performance of the large‐scale power systems. First, the linearized reduced‐order plant model is established, which efficiently considers the time delay of the remote feedback signals transmitted by wide‐area measurement systems. Then, based on the robust control theory, the design of the FACTS‐WARD controller is formulated as the standard control problem on delay‐dependent state‐feedback robust control, which is described by a set of linear matrix inequality constraints. Furthermore, in order to obtain the optimal control parameters that can endure the maximum time delay, a FWM approach is proposed to solve the time‐dependent problem of the time‐delay system. Meanwhile, an iterative algorithm based on cone complementary linearization is presented to search out the optimal control parameters. Finally, the nonlinear simulations on the 2‐area 4‐machine and the 5‐area 16‐machine test systems are performed, to evaluate the control performance of the proposed robust wide‐area time‐delay control approach. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

广域阻尼控制延迟特性分析及其多项式拟合补偿

基于广域测量系统(WAMS)的互联电网区间阻尼控制能够有效抑制区间低频振荡,提高互联系统的传输容量.采用远方反馈信号的广域阻尼控制系统需要解决的工程问题之一是研究数据传输过程中引入的延迟对控制性能的影响及其补偿方法.文中根据我国部分WAMS工程的通信延迟实测数据分析了WAMS延迟的特点,并针对广域阻尼控制设计了基于多项式拟合的预测方法补偿滞后的远方反馈信号.以一个典型的2区域4机系统为例研究了不同延迟条件对阻尼控制的影响和补偿效果.仿真表明:所提出的延迟补偿方法能够在一定延迟范围内有效地维持采用远方反馈信号的广域阻尼控制效果,为其工程应用奠定了基础.     

计及时延的互联电力系统分散式阻尼控制

针对广域互联电力系统的低频振荡问题,计及信号在广域控制回路中的时延,设计了一种分散式阻尼控制器。首先定性分析了广域控制回路中的信号时延特点,然后在计及时延的互联电力系统线性化模型基础上,使用时延依赖稳定性充分条件进行控制器的求解,最后进行了两区四机系统分散式阻尼控制器设计。在固定时延与随机时延情况下系统仿真结果表明所设计分散控制器能够有效提高系统阻尼,抑制系统低频振荡,提高互联电力系统的动态稳定性能。     

Stability and H∞ performance of multiple‐delay systems with successive delay components

This paper presents a new model for linear time‐delay systems with multiple delayed states where each delay contains finite number of successive components with different time‐varying properties, referred to as multiple‐delay system with successive time‐varying delay components (MDSSTDCs). General stability result and H_∞ performance conditions, under which the MDSSTDCs are asymptotically stable with certain H_∞ disturbance attenuation level, are derived by exploiting a general Lyapunov–Krasovskii functional and by making use of novel techniques for time‐delay systems. The result is applied to two special types of time‐delay systems frequently used in engineering applications and corresponding conditions for stability and H_∞ performance are obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

基于ε—权衡“阻尼—时滞”电力系统广域阻尼控制

在解决电力系统区间低频振荡时存在广域信号延迟问题,对系统稳定运行带来巨大影响。针对此问题,首先建立时滞电力系统降阶数学模型;然后提出一种基于权衡的思想实现广域阻尼控制,通过利用线性矩阵不等式（LMI）工具箱并借助李雅普诺夫时滞稳定性判据求解广域阻尼控制器（WADC）参数,再利用时滞分割间接方法证明系统的稳定性,并对系统阻尼特性进行分析。最后以四机两区模型为例进行仿真,结果表明在约6 s时转子角和有功功率基本趋于稳定,相比其他常用广域阻尼控制器方法有效地改善电力系统阻尼稳定性。     

Output‐feedback co‐ordinated decentralized adaptive tracking: The case of MIMO subsystems with delayed interconnections

Exact decentralized output‐feedback Lyapunov‐based designs of direct model reference adaptive control (MRAC) for linear interconnected delay systems with MIMO subsystems are introduced. The design process uses a co‐ordinated decentralized structure of adaptive control with reference model co‐ordination which requires an exchange of signals between the different reference models. It is shown that in the framework of the reference model co‐ordination zero residual tracking error is possible, exactly as in the case with SISO subsystems. We develop decentralized MRAC on the base of a priori information about only the local subsystems gain frequency matrices without additional a priori knowledge about the full system gain frequency matrix. To achieve a better adaptation performance we propose proportional, integral time‐delayed adaptation laws. The appropriate Lyapunov–Krasovskii type functional is suggested to design the update mechanism for the controller parameters, and in order to prove stability. Two different adaptive DMRAC schemes are proposed, being the first asymptotic exact zero tracking results for linear interconnected delay systems with MIMO subsystems. Copyright © 2005 John Wiley & Sons, Ltd.     

Multi‐objective optimization power control for code division multiple access systems

In code division multiple access (CDMA) communication systems, the communication channel is usually corrupted with time‐varying interferences, which include channel fading, multiple access interference, round‐trip delay, and noise. Power control is an important issue for CDMA systems to achieve higher communication link quality and better system capacity under time‐varying interferences. In the previous studies, most of power control algorithms only considered the user's target signal‐to‐interference‐and‐noise‐ratio (SINR) to maintain quality of service. In this study, a multi‐objective optimization method is proposed for power control design in CDMA systems. With a shadow system and an h _∞ filter to compensate for the round‐trip delay, the proposed power control scheme can simply adjust transmission power to achieve the best compromise between several objectives, such as minimization of SINR deviation, minimization of power consumption, and minimization of the system outage. Several simulation results are given to confirm the performance of the proposed power control scheme. Copyright © 2013 John Wiley & Sons, Ltd.     

基于线性矩阵不等式理论的广域电力系统状态反馈控制器设计

应用基于同步相量测量单元的广域测量系统进行广域控制时,反馈信号的传输时延是不能忽略的。作者根据实际电力系统的特点构造了部分状态含时延的状态反馈控制器,应用线性矩阵不等式理论提出了时滞依赖的稳定性条件,根据该条件不仅能得到保证系统稳定的控制器,而且可以得到保证系统稳定的最大允许时间延迟。最后以4机系统为例,用时域仿真的结果说明所得控制器的性能及该方法的有效性。     

Design of unknown‐input reduced‐order observers for a class of nonlinear fractional‐order time‐delay systems

This paper considers the design of reduced‐order state observers for fractional‐order time‐delay systems with Lipschitz nonlinearities and unknown inputs. By using the Razumikhin stability theorem and a recent result on the Caputo fractional derivative of a quadratic function, a sufficient condition for the asymptotic stability of the observer error dynamic system is presented. The stability condition is obtained in terms of linear matrix inequalities, which can be effectively solved by using existing convex algorithms. Numerical examples and simulation results are given to illustrate the effectiveness of the proposed design approach.     

Adaptive reconfigurable control of systems with time‐varying delay against unknown actuator faults

This work is concerned with the problem of delay‐dependent adaptive fault‐tolerant controller design against unknown actuator faults for linear continuous systems with time‐varying delay. Based on the online estimation of possible faults by discontinuous adaptation law, identification parameters of the adaptive state feedback controller are updated autonomously to compensate the fault effects on the delayed system. For the first time, a convex combination idea and a projection‐type adaptive approach are combined organically to derive the main results. A set of new delay‐dependent reconfigurable stabilization criteria, which guarantee the stability of closed‐loop systems in both fault‐free and faulty cases, is established in terms of linear matrix inequalities. Two numerical instances for linear delayed systems and the linearized model for the lateral motion of Boeing 747 are respectively simulated to illustrate the superiority and the effectiveness of the presented adaptive delay‐dependent results. Copyright © 2013 John Wiley & Sons, Ltd.     

An adaptive switching scheme for uncertain discrete time‐delay systems

In this paper, an adaptive switching control algorithm is proposed for the stabilization of uncertain discrete‐time systems with time‐varying delay. It is assumed that the time delay is unknown and time varying, nonetheless bounded with a known bound. It is supposed that the system is highly uncertain, and that a set of controllers are designed (off‐line) to stabilize the system in the whole uncertain parameter space; subsequently, a switching scheme is developed to stabilize the uncertain time‐delay system. A thorough stability analysis for the uncertain time‐delay system under the mentioned control scheme is provided. Furthermore, an upper bound on the allowable rate of change of the system parameters and delay is obtained. Simulation results are presented to show the efficacy of the proposed switching scheme. Copyright © 2008 John Wiley & Sons, Ltd.     

H∞ filtering for continuous‐time singular systems with time‐varying delay

This paper focuses on H_∞ filter design for continuous‐time singular systems with time‐varying delay. A delay‐dependent H_∞ performance analysis result is first established for error systems via a novel estimation method. By combining a well‐known inequality with a delay partition technique, the upper bound of the derivative of the Lyapunov functional is estimated more tightly and expressed as a convex combination with respect to the reciprocal of the delay rather than the delay. Based on the derived H_∞ performance analysis results, a regular and impulse‐free H_∞ filter is designed in terms of linear matrix inequalities (LMIs). A numerical example is given to demonstrate the merits of the proposed method. Copyright © 2010 John Wiley & Sons, Ltd.     

Midterm stability evaluation of wide‐area power system using synchronized phasor measurements

In recent years, the PMU (Phasor Measurement Unit) has received a great deal of attention as a synchronized measurement system of power systems. Synchronized phasor angles obtained by the PMU provide valuable information for evaluating the stability of a bulk power system. The aspect of instability phenomena during midterm tends to be more complicated, and the stability analysis using the synchronized phasor measurements is effective in order to keep a complicated power system stable. This paper proposes a midterm stability evaluation method for the wide‐area power system using synchronized phasor measurements. By clustering the power system to some coherent groups, step‐out is predicted on the basis of an aggregated two‐machine equivalent power system. The midterm stability of a longitudinal power system model of Japan's 60‐Hz systems constructed by a hybrid‐type power system simulator is practically evaluated using the proposed method. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(1): 25–32, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10274     

基于Pade近似的广域电力系统关键模态时滞轨迹分析

采用广域阻尼控制可有效地提高大型互联系统的动态性能,但广域信号传输带来的时滞对广域电力系统关键模态产生显著影响,从而改变闭环系统稳定性,因此关键模态时滞变化轨迹分析对于广域阻尼控制设计具有重要理论意义。首先采用Pade近似方法将时滞环节转化为状态空间表达式,从而建立考虑时滞环节的电力系统线性化模型;之后建立时滞对电力系统机电模态的影响关系模型;采用Arnoldi特征值计算方法研究时滞对区间振荡模态、局部振荡模态和时滞相关模态的影响规律。以四机两区域系统和New England系统为测试系统,仿真结果表明该方法能够较准确地求解上述模态随时滞变化趋势,从而验证了该方法的有效性。     

南方电网广域阻尼控制系统及其运行分析

广域控制是新一代大电网调控技术的发展方向.南方电网公司为提升区域间振荡阻尼,研发并安装了广域阻尼控制系统.该系统由位于6个500 kV站点的相量测量单元(PMU)、位于2个直流整流站的控制子站、位于总调的控制中央站以及广域控制和高压直流(HVDC)输电系统的接口组成,利用2回大容量直流的调制来改善电网动态稳定性.文中介绍了广域阻尼控制系统的设计思路、总体概况、系统的开环试运行情况,详细分析了2次闭环大扰动试验的结果.运行与试验表明该系统完全达到了增强区域间振荡阻尼的设计目的.     

智能电网环境下分布式阻尼控制器设计

智能电网以广域测量系统作为支撑,通过信息的相互关联来有效控制电网稳定运行。在智能电网环境下,针对广域互联电力系统的低频振荡问题,利用分布式网络控制的灵活特性,研究设计一种计及时延的分布式阻尼控制器。考虑将测量信息作为阻尼控制器的输入信号,只涉及到本地及相邻通信节点的信息,进而基于图论新颖法对分布式阻尼控制器输入信号的通信拓扑特性进行描述。在设计广域系统中控制器时考虑到了远程信号的传输时延,并利用其时延依赖稳定性这一充分条件。最后运用到四机两区系统的仿真对比结果,显示本文提及的分布式阻尼控制器不仅使系统阻尼得到有效提高,还体现出局部与区域间低频振荡以及传输线功率振荡的可抑制性,增强了融合电力信息系统的稳定性。     

Optimization and coordination of wide-area damping controls for enhancing the transfer capability of interconnected power systems

This paper proposes systematic procedures to design wide-area damping controls (WADCs) in large interconnected power systems. An efficient model reduction method is first introduced, based on the pseudo-random binary signal (PRBS) probing technique and the prediction error identification algorithm (PEM). Then, the comprehensive controllability concept, as well as its calculating method, is proposed for properly locating the supplementary damping controllers. Further, an improved modal performance index is adopted as the measure of the stabilizing effect. With various constraints taken into account to meet practical engineering requirements, finally, the optimized and coordinated tuning of WADC parameters under various operation scenarios is achieved by a constrained nonlinear programming algorithm. The proposed approach has been tested on a practical 437-machine, 2791-node interconnected power system and the simulation results have demonstrated its high effectiveness in damping inter-area oscillations and enhancing across-region transfer capabilities.     

A robust centralized SMES controller design based on WAMS considering system and communication delay uncertainties

It is well known that the communication delay due to the phasor measurement in wide area monitoring system (WAMS) as well as various system operating conditions such as heavy line flows and unpredictable network structures, may deteriorate the wide-area stabilizing control effect. To overcome this problem, the inverse input and output multiplicative model is proposed to represent unstructured uncertainties due to system operations and communication delay in the robust centralized damping controller design of superconducting magnetic energy storage (SMES) based on WAMS. The structure of centralized controller for SMES is the practical 1st-order lead/lag compensator. To automatically tune the control parameters, the optimization problem based on the enhancement of damping performance and system robust stability margin is achieved by particle swarm optimization. Simulation studies in the West Japan six-area interconnected system confirm that the proposed robust SMES centralized controller is superior to the conventional SMES centralized controller in terms of damping performance and robustness against system and time delay uncertainties.     

A small‐gain approach for adaptive output‐feedback NN control of switched pure‐feedback nonlinear systems

This paper investigates the problem of adaptive output‐feedback neural network (NN) control for a class of switched pure‐feedback uncertain nonlinear systems. A switched observer is first constructed to estimate the unmeasurable states. Next, with the help of an NN to approximate the unknown nonlinear terms, a switched small‐gain technique‐based adaptive output‐feedback NN control scheme is developed by exploiting the backstepping recursive design scheme, input‐to‐state stability analysis, the common Lyapunov function method, and the average dwell time (ADT) method. In the recursive design, the difficulty of constructing an overall Lyapunov function for the switched closed‐loop system is dealt with by decomposing the switched closed‐loop system into two interconnected switched systems and constructing two Lyapunov functions for two interconnected switched systems, respectively. The proposed controllers for individual subsystems guarantee that all signals in the closed‐loop system are semiglobally, uniformly, and ultimately bounded under a class of switching signals with ADT, and finally, two examples illustrate the effectiveness of theoretical results, which include a switched RLC circuit system.     

考虑广域信息时延影响的H∞阻尼控制器

广域控制策略可以有效提高广域分布互联电力系统的动态性能,但是广域控制信号传输时延会对控制器产生负面影响,并且日趋复杂的系统结构及接近稳定极限的运行条件对控制器的鲁棒性能提出了更高的要求。该文在考虑信号传输时延的情况下建立了电力系统状态空间模型,并应用H∞回路成形及规范互质分解技术对上述模型进行了鲁棒镇定控制器设计。得到的控制器不仅具有很强的鲁棒性能,同时可使闭环系统容忍更大的时延。以时域仿真结果说明了所得控制器的性能及方法的有效性。