Robust controller design for large interconnected power systems with model uncertainties based on wide-area measurement

Recently the controller using wide-area measurement systems (WAMS) signals has been suggested to accommodate the dynamic performances of large interconnected power systems. However, there is an unavoidable delay before the wide-area signals are received at the controller site. Therefore, a delay-independent robust control problem of large interconnected power systems is studied via H _∞ fuzzy control method based on wide-area measurement. First, a set of equivalent Takagi–Sugeno (T–S) fuzzy model is adopted to represent the nonlinear large interconnected power system. A wide-area state feedback decentralized H _∞ fuzzy control scheme is developed to override the various disturbances, solve the effect of model uncertainties and stabilize the large power system. The H _∞ decentralized control problem is parameterized in terms of a linear matrix inequality (LMI) problem, and the LMI problem can be solved efficiently using convex optimization techniques. Finally, the effectiveness of the proposed controller design methodology is demonstrated through simulation example. This work is supported by the National Science Foundation of China under grant 60374039, 60404007.     

Improvement of transient stability for power systems using wide-area measurement signals

With the wide application of synchronized phase measurement unit in power system, the wide-area measurement (WAM) system has enabled the use of a combination of measured information from remote location for improving transient stability. The paper focuses on a two-level hierarchical decentralized coordinated excitation control consists of multiple decentralized local fuzzy power system stabilizers (LFPSS) for each generator at the first level helped by a WAM based supervisory power system stabilizer (SPSS) at the secondary level for wide-area power system transient stability enhancement. In order to eliminate the inherent nonlinearities in the power system model and enable the model to be applicable to power system control, first, a direct feedback linearization compensator acting through the local excitation machine is proposed. Then, the T-S fuzzy model is employed to approximate the system model. Based on the T-S fuzzy model, the LFPSS is designed. And the SPSS is proposed to apply the remote signals from the WAM systems. For taking consideration of the time delays introduced by remote information’s transmission in WAM systems and overcoming their impacts on control performance, the authors develop a delay-independent H _∞ robust control technique. Some new robust stability criteria in terms of LMI are derived by Lyapunov stability theory incorporating LMI techniques. Simulation examples demonstrate that the decentralized coordinated robust control has better transient stability performance in the face of transmission time delays, severe variations of operating point and faults in various locations.     

基于WAMS的电网稳定控制中的时滞问题及一种控制策略

基于广域测量系统(WAMS)的大电网稳定控制是目前学术和工程界的研究热点。在WAMS环境中,一个不容忽视的问题就是PMU信号传输和处理过程中时滞的影响。介绍了同步相量测量技术和以此为基础的广域测量系统的四种结构,分析了PMU信息对区域电网控制的影响,在此基础上针对PMU信息滞后的特点提出了一种闭环区间阻尼控制策略。     

基于模糊控制的广域阻尼控制器设计

针对互联电力系统低频振荡问题,提出了一种用广域反馈信号作为附加稳定信号的励磁控制器的设计方法。广域信号传输存在的通信时滞用模糊控制方法进行补偿。描述了确定模糊推理规则的方法,首先分析模糊逻辑控制器的输入量和理想输出量,根据输入量和输出量之间的关系确定模糊论域、隶属度函数和模糊推理规则,从而建立模糊逻辑控制器。用Matlab/Simulink软件对4机2区域系统进行仿真,测试模糊广域阻尼控制器性能。仿真结果表明,所设计的控制器能补偿通信过程中存在的较大时滞,增加互联电力系统阻尼。仿真结果验证了模糊控制具有较好的鲁棒性和适应性。     

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.     

不健全广域信息下时滞非线性鲁棒综合控制器设计

同步相量测量单元(PMU)在电力系统中的广泛应用为基于广域测量系统(WAMS)的广域控制提供了实现条件。由于远方反馈信息的不健全和时滞影响，基于广域信息的闭环电力系统将是一个时滞非线性系统。针对这种时滞非线性系统，结合逆系统理论和鲁棒H￥控制理论，提出不健全广域信息下考虑时滞影响的非线性鲁棒综合控制器的设计方法。首先，应用逆系统方法将强非线性电力系统进行线性化，然后，根据广域信息的不确定性，推导具有干扰输入的时滞线性系统模型，最后，应用线性矩阵不等式(LMI)理论设计该线性系统的鲁棒反馈控制律，进而得到原非线性电力系统的最终控制规律。时域仿真结果表明，当考虑广域信息的不健全和时滞影响时，非线性鲁棒综合控制器仍具有较小的系统过渡时间、振荡次数及振荡幅度，能大幅度增加系统的故障临界切除时间。     

采用广域测量信号的互联电网区间阻尼控制

在大型互联电力系统中，区间模式的低频振荡是限制传输能力的严重瓶颈之一，而经典阻尼控制(如PSS)因限于局部测量不能很好地解决这个问题。迅速发展的广域测量系统能在全网范围内精确测量和高速传递机组相对功角和角频率等量，使得采用广域测量信号构成全局性的区间阻尼控制系统成为可能，进而为提高互联电网的功角稳定性和传输容量提供了契机。文中在一个简单的2区4机电力系统中，研究了采用广域测量信号实现励磁控制器区间阻尼控制环节的设计原理、实现方法和仿真效果，说明了基于广域测量系统的区间阻尼控制能有效抑制区间低频振荡和提高互联系统的传输容量，而且可工程实现。同时就设计适用于复杂电力系统的广域阻尼控制系统提出了一些关键性理论和实际问题，以供进一步深入研究。     

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.     

计及时滞丢包综合特性的电力系统小干扰稳定分析与控制

广域测量系统(WAMS, wide-area measurement system)给提高大规模互联电网的小干扰稳定性提供了新的手段。本文针对其中普遍存在的时滞丢包现象,用数学期望的方法建立了其统一的数学模型,推导出考虑丢包的等效时滞,从而量化了丢包对小干扰稳定的影响。基于此模型,结合状态观测器和时滞依赖状态反馈鲁棒控制,充分考虑时滞的随机性,进行附加阻尼控制器设计。以两区四机系统和某大电网为算例,对不同的丢包率和时滞以及按照不同模型进行仿真,仿真结果验证了模型的正确性。所设计的阻尼控制器能够充分考虑时滞丢包的综合特性,有较好的鲁棒性,这对抑制区域间振荡和应用广域测量系统有着重要的意义和参考价值。     

一种简单实用的分散非线性励磁控制方法

基于广域测量系统（WAMS）提供的电力系统惯量中心（COI）数据,建立了COI参考坐标系下完全解耦的发电机模型,并根据Lyapunov理论和反步法思想,提出了一种简单实用的分散非线性励磁控制设计方法。该方法原理简单,仅有的3个控制器参数设置非常容易;此外,需要WAMS传送至发电机的控制信号只有3个,降低了信道拥堵的可能性。新英格兰测试电力系统（NETPS）中的仿真结果表明,这种非线性励磁控制器不仅对发电机参数、运行状态和负荷类型具有良好的鲁棒性,而且允许COI信号存在时滞,允许时滞的类型和范围基本能覆盖正常情况下的WAMS数据延时。     

计及广域测量系统时滞影响的TCSC控制器设计

在广域电力系统的环境下，基于相量测量单元技术的广域测量系统将引入不可忽略的时滞，这将对基于广域测量系统测量信号的广域控制器带来影响，从而对电力系统的动态特性产生重大的影响。分析了广域测量系统的通信延迟时间对可控串联电容补偿器(TCSC)非线性控制器稳定特性的影响，基于线性矩阵不等式理论设计了TCSC控制器以提高电力系统对时滞的不敏感性，线性和非线性时域仿真结果验证了所设计的TCSC控制器的有效性。     

交直流互联系统鲁棒自适应直流功率调制

设计了应用于交直流互联电力系统的直流功率调制的非线性鲁棒自适应控制器。该控制器基于驱动各互联区域电网的惯量中心至统一平衡点的设计思想，采用广域测量系统的全局信号，用以阻尼交直流互联系统的区域间功率振荡。采用反步法设计的自适应鲁棒控制规律使控制器对未知参数具有自适应性，对模型误差、扰动和平衡点变化具有较强的鲁棒性。仿真结果表明，与传统的线性直流功率调制控制器相比，该控制器对联络线的功率振荡具有优良的阻尼性能，可显著提高输电极限，而且能很好地适应运行点的变化。     

广域保护(稳控)技术的现状及展望

在电网保护控制中,稳控系统是基本定位于常规保护及数据采集和监测控制系统/能量管理系统(SCADA/EMS)之间的系统保护控制手段,是互联大电网不可少的保护措施.1965年北美大停电后,开始了这类系统装置的开发应用,到80年代已积累了不少的实际运行经验.各大电网的规划、运行、调度均对这类系统的功能及运行提出了明确的要求.随着计算机技术及通信技术的发展,新一代的稳控技术正在形成,这就是基于广域测量系统及在线动态安全分析的广域保护.广域测量系统已经在北美运行5年以上,而基于广域测量系统的稳定控制及其它应用也逐渐在实际电网中有一些试运行的成果.     

采用时滞广域测量信号的区间低频振荡阻尼控制器设计

针对电力系统区间低频振荡问题,基于广域测量系统和柔性交流输电系统技术,提出了一种采用时滞广域测量信号的电力系统阻尼控制器设计方法。该方法结合时滞依赖状态反馈鲁棒控制和状态观测理论,实现了广域电力系统的时滞输出反馈鲁棒控制。以四机两区域电力系统为例,设计了晶闸管可控串联补偿(TCSC)附加阻尼控制器。小信号分析和时域仿真结果都表明:所设计的控制器能显著抑制区间低频振荡,并且具有时滞不敏感性和运行条件鲁棒性。     

计及时滞影响的水轮发电机调节系统的广域H∞控制

研究了水轮发电机调节系统的广域H∞控制,探讨利用线性矩阵不等式（linear matrix inequality,LMI）进行H∞控制器设计的方法及步骤。除计及时滞影响外,还考虑了外部扰动和建模误差等不确定因素。以联接到远方系统的水轮发电机为例,进行了存在广域测量系统（wide area measurement system,WAMS）时滞影响的水轮发电机调节系统的H∞控制器设计。仿真及分析表明,所设计的控制器在一定范围内具有对时滞的不敏感性,可以抑制外部干扰,保持电力系统的动态稳定。     

考虑广域测量时滞的广义预测电网阻尼控制

针对大型电力系统模型的复杂性和时变性使得离线计算结果可靠度不高的问题,利用广域测量条件下数据实时同步高速采集的优点,将广义预测控制理论应用于电网阻尼控制系统,提出一种适用于广域测量条件的电力系统阻尼控制器设计方案,以实现系统的实时监测、滚动优化和反馈控制。该方案引入预估补偿器以克服远方反馈信号的时滞对控制性能的影响;通过在线辨识参数不断修正广义预测控制器模型和预估器参数进行优化控制,达到改善互联电网阻尼、抑制低频振荡的目的。基于EPRI 36节点系统和国内某实际电网的仿真试验结果证实了控制方法的有效性。     

Design of power system stabilizer using observer/sliding mode, observer/sliding mode-model following and H∞/sliding mode controllers for small-signal stability study

This paper presents a power system stabilizer (PSS) for a small-signal stability study using three kinds of controllers to solve the problem of the unmeasurable state variables in the conventional sliding mode control (SMC): first the observer/sliding mode control (O/SMC), second the observer/sliding mode-model following control (O/SM-MFC) and third the H_∞/sliding mode control (H_∞/SMC). The values of the output vector are obtained by measuring angular velocity only and can eliminate the need to measure all the state variables in the conventional SMC-PSS. The estimated control inputs are derived by Lyapunov's second method that keeps the system stable. The effectiveness of the proposed controller is verified by linear time-domain simulation under normal load operation and under parameter variation of the AVR gain K_A.     

A study on robust adaptive modulation controller for TCSC based on COI signal in interconnected power systems

This paper proposes a novel robust adaptive modulation controller (RAMC) for thyristor controlled series capacitor (TCSC) in interconnected power systems to damp low frequency oscillation. The main idea of the controller is to drive the area centers of inertia (COI) to a stable equilibrium point and keep system synchronization. COI-coordinate-based model is derived first. Then RAMC for TCSC is derived using back-stepping method with COI dynamic signals from WAMS. The new controller performance is tested through a three-area power system and the simulation results show clearly that the new controller using COI signals has superior performance as compared with the conventional controller.     

考虑时滞影响的电力系统广域集中励磁控制

针对电力系统区间低频振荡问题,构建了广域集中励磁控制(wide-area centralized excitation control,WCEC)框架。在充分考虑时滞影响的前提下,根据时滞输出反馈鲁棒控制理论设计了WCEC。广域测量系统实时测量反映区间低频振荡的状态变量,并将其传送至WCEC进行计算分析,WCEC把全局控制信号传送给相关机组的励磁系统,以此阻尼电力系统区间低频振荡。4机2区域电力系统的频域分析和时域仿真表明,WCEC在较宽的时滞区间内提高了系统的阻尼值,能够快速有效地抑制区间低频振荡,并且具有对运行状况的鲁棒性和对时滞类型的不敏感性。     

互联电力系统模糊负荷频率控制器的优化设计

通过建立一个改进了的带修正因子的模糊（ｆｕｚｚｙ）控制表的数学表达式和一个综合性能指标，提出了一种互联电力系统分散Ｆｕｚｚｙ负荷频率控制器的自动优化设计方法。对一个两区域互联电力系统的数字仿真结果表明：所设计的分散Ｆｕｚｚｙ负荷频率控制器具有良好的控制性能。