一种适用于小干扰分析的在线负荷建模方法

负荷模型对小干扰稳定分析影响很大,然而目前的负荷建模方法利用大扰动的响应数据建立负荷模型,由于负荷具有时变性,大扰动时刻建立的负荷模型不能等效于替他时刻的负荷模型,故不适用于其他时刻的小干扰稳定分析。为解决上述问题,基于子空间法提出一种适用于小干扰分析的在线负荷建模方法。首先选择时时存在的类噪声信号作为辨识信号,并采用子空间法在线辨识负荷的状态空间模型,旨在通过在线建模解决由负荷时变性导致负荷模型不准确的问题。但是子空间法建立的负荷状态空间模型并不是实际负荷的状态空间模型,二者存在未知的线性变换,采用解析的方法证明了上述未知线性变换不影响小干扰分析的结果,从而说明所提出的负荷建模方法适用于小干扰分析。最后,在10机39节点系统验证了方法的有效性。     

基于子空间辨识和遗传算法的多回直流协调阻尼控制器设计

提出了一种多回直流协调阻尼控制器的设计方法,用子空间辨识法对系统降阶建模,用遗传算法进行参数寻优,并对时滞系统稳定性进行了评估。首先利用基于Prony分析的主模比指标计算法选择直流控制器的广域输入信号,通过仿真得到扰动下系统输入输出数据,基于数据对系统进行子空间辨识,得到系统开环状态空间方程。其次将控制器加入开环系统得到闭环系统状态空间方程,以多种运行方式下的系统最小阻尼比最大化为优化目标,针对闭环系统状态空间方程,用遗传算法对控制器参数进行协调优化。采用基于自由权矩阵的时滞稳定性判据,分析含有多回直流协调控制器的广域电力系统的时滞稳定性。最后以南方电网为例,对多回直流协调阻尼控制器进行仿真,仿真结果表明,通过该方法所得到的多回直流协调阻尼控制器能够较好地提高电网阻尼水平,并满足时滞系统稳定性的要求。     

基于MIMO辨识的复杂系统多控制器最优设计

由于互联电网低频振荡的全局性质,各种阻尼控制器必须协调设计,但对于实际大规模电网,作为设计基础的系统模型难以获取,提出了一种基于辨识的最优协调设计方案.通过注入的带宽信号(0.1～3 Hz,已包含整个机电振荡模式频率范围)激发动态稳定控制相关的系统特性,采用预测误差方法(PEM)辨识得到复杂系统的多输入多输出(MIMO)降阶模型.通过引入额外的状态量和输出量改进传统的线性最优控制设计方法,使其控制器结构中可包含领先一滞后环节,而不仅仅是比例环节,并给出了扩展后的系统方程及控制器参数计算方法.上述方案通过2条直流线路的调制控制器设计进行了验证,其中MIMO降阶模型辨识时曲线拟合度可达80%以上.     

基于同伦变换的VSC-HVDC分散协调鲁棒阻尼控制器设计

针对含柔性直流的区域互联电力系统低频振荡,提出一种基于同伦变换的有功、无功分散协调控制方法。首先,通过数字子空间状态空间系统辨识算法辨识出系统多输入多输出(multiple input multiple output,MIMO)状态空间模型,并对系统进行振荡模态分析。其次,基于线性矩阵不等式鲁棒控制理论,设计出集中MIMO附加鲁棒控制器。最后,应用同伦变换将集中MIMO鲁棒控制器转化为分块对角化的结构,从而得到多个低阶单输入单输出鲁棒控制器。仿真验证表明,该文所设计的有功、无功相协调的分散鲁棒控制器能有效抑制低频振荡,控制器阶数低,无耦合,鲁棒稳定性强,在严重故障情况下能充分利用基于电压源换流器的直流输电的有功和无功调制能力,并且在信号丢失时能保持较好的阻尼性能。     

基于改进子空间模型辨识法的交直流系统降阶模型在线辨识

广域测量系统(WAMS)的发展使得交直流系统模型在线辨识成为可能。基于加快辨识速度以及准确自适应定阶的考虑,提出了改进子空间辨识方法。通过交直流系统机侧、网侧最佳控制点以及最佳观测点的选择确定输入输出信号点,并在输入点注入带通信号以激发低频振荡模态,从而得到系统振荡模态的输出响应信号。改进子空间方法可同时根据输入输出信号得到系统降阶模型,而多种故障条件下Kalman预估器的估计信号与实际信号的接近程度则可验证方法的鲁棒性。8机36节点交直流系统的仿真结果表明,该方法能够准确、有效辨识出交直流系统降阶模型,为交直流系统中央协调阻尼控制器的设计奠定了基础。     

基于子空间法的电网暂态频率扰动惯量估计

针对暂态频率扰动下传统惯量估计方法受扰动发生时刻和惯性响应持续时间判断敏感而导致估计误差偏大的问题,文章提出基于子空间法的电网惯量估计思想。通过分析暂态频率扰动发生前、惯性响应及一次调频响应各阶段的电网频率响应模型的冲激响应特征,获得各阶段的电网惯量统一性表达,并将各阶段电网频率响应模型作为相同待估计系统,应用子空间法进行系统模型参数辨识,最终估计出电网惯量。通过算例分析验证了文章方法对电网惯量估计的有效性及精确性。     

数字PI控制器的参数辨识及实验验证

风电机组控制系统中PI控制器较多,需要辨识各PI控制器的参数。针对数字PI控制器,基于可辨识性理论,直接应用PI控制器不同状态的输入/输出数据,分析PI控制器参数的可辨识性,得到了其参数可唯一辨识的结论,并据此设计了PI参数辨识的具体算法。在此基础上,根据电机转速控制实验装置实测的数据,运用可辨识性分析步骤中的参数辨识算法,辨识得到高精确度的PI参数。在施加脉冲群干扰试验和振荡波干扰试验条件下,算法也能准确地辨识PI控制器参数,具有良好的鲁棒性,验证了理论分析的正确性和辨识方法的可行性。     

随机数据驱动下的机电振荡参数在线提取与阻尼调制(一):基于ORSSI的模态参数在线辨识

随机响应数据蕴含丰富的动态信息,从随机响应数据可提取机电振荡特征参数、进行小干扰稳定分析。该文在环境激励电力系统随机响应特征分析基础上,提出了基于在线递归随机子空间辨识法(on-line recursive stochastic subspace identification,ORSSI)的电力系统小干扰稳定性在线评估方法。ORSSI辨识算法利用LQ分解取代了传统SSI算法中的奇异值分解过程,有效地提高了计算速度,同时通过引入Givens旋转变换,替代数据更新后Hankel矩阵LQ分解过程,实现了延伸观测矩阵在线更新,在保证计算精度的同时提高了机电小干扰稳定评估的实时性。基于IEEE 16机68节点系统和某实际系统的仿真,验证了文中方法的可行性和有效性。     

基于迭代PRONY算法的传递函数辨识

该文介绍了一种辨识电力系统降阶线性模型的方法：通过迭代方法来提高传统Prony分析的精度，并利用特定的输入信号，使Prony分析可以进行传递函数辨识。将其用于电力系统稳定器(PSS)设计过程中传递函数的辨识，不仅可辨识出系统的降阶模型，同时还可估计系统的初始状态。由于这些传递函数中包含系统中其它机组及控制器的信息，故利用该方法进行PSS设计，便于实现多机协调控制，极大地扩展了此方法在实际系统中的应用范围。文中最后通过2个算例验证了该方法的有效性。     

采用IMC-PID增强超临界机组功率控制的鲁棒性

介绍了一种机组协调控制系统,其在汽轮机主控回路中采用基于闭环辨识模型的IMC-PID方法,采用该方法解决火电机组功率振荡的问题。该方法首先通过闭环回路的设定值阶跃扰动试验,对测取的试验数据进行频率响应特性辨识,估计闭环控制过程中的频率响应矩阵和变换函数矩阵,用最小二乘法计算得出被控对象的模型。然后基于辨识出的模型,通过使用内部模型控制(IMC)方法,设计出汽轮机主控回路的鲁棒 PID 控制器。火力发电厂现场实际应用表明:汽轮机主控采用IMC-PID 控制器后,具有较好的鲁棒性,能够较好地抵御各种电网的外扰及发电过程内扰的影响,避免机组功率振荡。     

负荷激励下的互联系统振荡稳定性在线辨识

电力系统振荡稳定性辨识的传统方法是利用人工扰动试验或外加激励信号激发系统的,这种方法妨碍了电力系统正常运行.因此,以负荷随机波动为激励信号辨识电力系统振荡稳定性被认为是实现电力系统在正常工况下"全天候"振荡监测的途径.本文首先指出了电力系统在线辨识需要解决的若干关键问题,然后提出并证明了负荷波动作为激励信号的可行性,并将子空间算法应用于电力系统MIMO模型的辨识.为了大幅度减小辨识模型阶次,根据模式解耦性提出了互联电力系统的区域分割辨识方案.最后,以一个8机4区域电力系统为例,对所提方案进行了验证,证明该方法可以准确地识别出电力系统的特征值及模态振型.     

Optimal expansions of multivariable ARX processes on Laguerre bases via the Newton–Raphson method

In this article, an optimal linear MIMO system approximation by using discrete‐time MIMO autoregressive with exogenous input (ARX) model is proposed. Each polynomial function of the MIMO ARX model associated with the inputs and with the outputs is expanded on independent Laguerre orthonormal basis. The resulting model is entitled MIMO ARX–Laguerre model. The optimal approximation of which is ensured once the poles characterizing each Laguerre orthonormal basis are set to their optimal values. In this paper, a new method to estimate, from input/output measurements, the optimal Laguerre poles of the MIMO ARX–Laguerre model is proposed. The method consists in applying the Newton–Raphson's iterative technique in which the gradient and the Hessian are expressed analytically. The proposed algorithm is tested on a numerical example and on a benchmark system. Simulation results show the effectiveness of the proposed optimal modeling method. Copyright © 2015 John Wiley & Sons, Ltd.     

基于状态观测器的电力系统阻尼控制

研究了基于状态观测器的电力系统阻尼控制器设计方法.建立了包含4阶发电机模型和3阶励磁系统模型的多机电力系统线性化状态方程,并计算出其矩阵A的特征值和系统阻尼比.通过观察系统的阻尼强弱,根据所要求配置的极点,采用全维和降维状态观测器方法,求出观测器增益和系统反馈增益进行反馈控制.该方法的优点在于不需要测量系统的所有状态变量.在4机2区算例中,求出2种观测器的综合闭环系统的零输入响应,通过比较估测值与实际值的变化情况,验证了该方法改善电力系统阻尼特性的有效性.     

Neural network–based direct adaptive robust control of unknown MIMO nonlinear systems using state observer

This paper focuses on the problem of adaptive robust tracking control for a class of uncertain multiple-input and multiple-output (MIMO) nonlinear system. Unlike most previous research studies, model dynamics, disturbances, and state variables are unknown in this paper. A novel observer-based direct adaptive neuro-sliding mode control approach is proposed of which the only required knowledge is the system output. By incorporating the Adaptive Linear Neuron (ADALINE) neural network (NN) into the conventional sliding mode observer, the proposed observer has favorable performance. In the controller, a radial basis function (RBF) NN is constructed to approximate the unknown equivalent control laws and the estimation of the sliding surface is applied as the input. A gain-adaptation sliding mode term is designed to enhance the robustness of the control system. Besides, the free parameters of the ADALINE NN and the RBFNN are updated online by adaptive laws to obtain optimal approximation performance. Finally, the comparative simulations are given to show the effectiveness and merits of proposed scheme.     

Feedback stabilization for AC/DC power system with nonlinear loads

In view of the nonlinearity of loads and HVDC in power systems, the M derivative, M bracket and multi-input multi-output (MIMO) feedback linearization based on nonlinear differential algebraic system (NDAS) are introduced into the design of nonlinear controller for parallel AC/DC power system. Bronovsky normal form for NDAS is derived when the M relative degree of NDAS is less than its dimension and certain designated conditions are satisfied. The control laws of both the excitation system and the rectifier current control for AC/DC system are studied in depth which combine the input-output linearization technique and zero dynamics design theory for NDAS. The simulation for a single-machine infinite bus system (SMIBs) with parallel AC/DC transmission lines shows that the nonlinear control (NLC) strategy is able to improve system dynamic performance for a variety of system operating conditions.     

State-variable approach to analysis of power systems including HVDC convertors

A new method is presented for the analysis of power systems including static convertors. The basic feature of the proposed method is that the state equations of each component of a power system can be written separately by considering fictitious sources at their terminals. The values of these sources are calculated from a general algebraic connection equation, applied to any practical system bus and derived by using Kirchhoff's laws. Any model of the system components is easily incorporated using this technique and the response of the whole system is recorded at the expense of less computer time and memory.     

Robust nonlinear adaptive backstepping excitation controller design for rejecting external disturbances in multimachine power systems

This paper proposes a new approach to design a robust adaptive backstepping excitation controller for multimachine power systems in order to reject external disturbances. The parameters which significantly affect the stability of power systems (also called stability sensitive parameters) are considered as unknown and the external disturbances are incorporated into the power system model. The proposed excitation controller is designed in such a way that it is adaptive to the unknown parameters and robust to external disturbances. The stability sensitive parameters are estimated through the adaptation laws and the convergences of these adaptation laws are obtained through the negative semi-definiteness of control Lyapunov functions (CLFs). The proposed controller not only provides robustness property against external disturbances but also overcomes the over-parameterization problem of stability sensitive parameters which usually appears in some conventional adaptive methods. Finally, the performance of the proposed controller is tested on a two-area four machine 11-bus power system by considering external disturbances under different scenarios and is compared to that of an existing nonlinear adaptive backstepping controller. Simulation results illustrate the robustness of the proposed controller over an existing one in terms of rejecting external disturbances.     

计及非线性负荷的AC/DC系统控制策略

详细研究了带非线性负荷的交直流并联系统发电机励磁控制和直流系统控制,将M导数、M括号以及MIMO微分代数系统反馈线性化技术应用到交直流并联多机系统非线性控制器设计中,提出了具有微分代数形式的零动态设计.通过合理选择输出量作为坐标变换量,得到微分代数系统模型的Bronovsky标准形式.针对一个含有AC/DC的多机系统进行仿真, 研究结果表明,所设计的非线性控制器与传统的PID控制器相比具有较好的阻尼特性, 该控制器能进一步提高系统的动态稳定性.     

A New Design of Wide-Area MIMO Coupling Robust HVDC Supplementary Controller

A new multi-input multi-output (MIMO) robust coordination approach for the controller design of multi-infeed high voltage direct current (HVDC) system is proposed. This design will enhance the damping of certain low frequency oscillation mode. The dominant mode ratio (DMR) is applied to choose the appropriate feedback signals, while time delay of wide-area signals is considered. The Total Least Squares-Estimation on Signal Parameters via Rotational Technique (TLS-ESPRIT) algorithm serves in identifying the MIMO system model. To reach the best control effect and disturbance suppression level, the mixed H₂/H_∞ robust theory with regional poles placement is introduced to design the controller. The new MIMO design approach avoids system decoupling in complex situation, and it uses the interactions of different control loops to enhance the system's stability when most MIMO HVDC controllers are designed by decoupling strategy. Simulation results of a multi-infeed HVDC system validate the control effect and robustness of the proposed method.     

除氧系统模糊控制器的设计与实现

结合某炼油厂动力站除氧系统改造工程项目，以除氧系统的计算机控制为例，介绍了模糊控制器的设计与实现。除氧系统具有多输入多输出、大滞后、时变性、非线性等一系列特点，除氧器的水位和压力相互影响，是一强耦合系统，其精确数学模型难以建立。为了达到除氧目的，必须保证水位和压力的恒定，而常规的基于PID算法的控制器很难保证运行指标。为此，提出了一种基于模糊控制理论的多维模糊控制器的设计方法，并设计了除氧器压力和水位模糊控制器。为了消除多台除氧器并联工作时相互间的影响，控制各除氧器平稳运行，结合人工控制经验设计了智能控制器，其控制效果达到了预期要求。文中提出的模糊控制器，其设计过程简单，易于工程实现，适用于同类多输入多输出模糊控制器的设计。