Transient stability hierarchical control in multimachine powersystems

The authors present the optimal transient stability control problem in a hierarchical structure for multimachine power systems. The two-level structure retains the local closed-loop controls, thereby easing its implementation on existing systems. The formulation accounts for nonlinearities and interconnections, and the optimization of the system transient performance is obtained with less computational effort. Since the computations are distributed among the many local feedback subsystems, the storage and solution times are considerably less than those required by a single overall centralized controller. This advantage becomes much stronger as the system size increases. For illustration purposes, this technique was applied successfully to a four-machine system     

Transient stability enhancement and voltage regulation of powersystems

Improvement of the transient stability and voltage regulation of a single-machine-infinite-bus power system under the effects of a symmetrical three-phase short-circuit fault is detailed. The dynamical model of the system is described. A design strategy for nonlinear controllers is considered, and the design of a nonlinear variable-structure excitation controller is described. Simulation results obtained using the nonlinear excitation controller are given, and a new nonlinear coordinated controller is proposed. Simulation results obtained by using the nonlinear coordinated controller are presented     

A hybrid neuro-fuzzy power system stabilizer for multimachine powersystems

A fuzzy basis function network (FBFN) based power system stabilizer (PSS) is presented in this paper to improve power system dynamic stability. The proposed FBFN based PSS provides a natural framework for combining numerical and linguistic information in a uniform fashion. The proposed FBFN is trained over a wide range of operating conditions in order to re-tune the PSS parameters in real-time based on machine loading conditions. The orthogonal least squares (OLS) learning algorithm is developed for designing an adequate and parsimonious FBFN model. Time domain simulations of a single machine infinite bus system and a multimachine power system subject to major disturbances are investigated. The performance of the proposed FBFN PSS is compared with that of conventional (CPSS). The results show the capability of the proposed FBFN PSS to enhance the system damping of local modes of oscillations over a wide range of operating conditions. The decentralized nature of the proposed FBFN PSS makes it easy to install and tune     

Investigations of voltage flicker in electric arc furnace powersystems

Operation of rapidly varying loads such as AC and DC arc furnaces in large industrial power systems will cause voltage flicker on the utility system. System planning will help in determining the available short-circuit duty at the point-of-common-coupling to keep the voltage flicker within acceptable limits. Perceptible flicker limit curves are useful in determining the amount of flicker in a system. Short-circuit voltage depression calculation is one technique to estimate the amount of expected flicker in a system. On-site field tests with equipment that will accurately capture multiple frequencies will aid in measuring the existing voltage flicker. The authors discuss flicker estimation and field tests as well as harmonic filter tuning effects on voltage flicker. The ultimate determination whether unacceptable voltage flicker exists in a system will be complaints from customers served by the utility system actually experiencing objectionable or noticeable flicker     

考虑极限诱导分岔的电压稳定研究

研究由于电力系统变量限制导致的极限诱导分岔对电压稳定的影响.给出了发生极限诱导分岔可能出现的条件.提出了变量达到输出极限导致极限诱导分岔时,影响系统电压稳定与否的判据,该判据改变了传统上用求解雅克比矩阵特征值的方法来判断电压稳定性,转而用收敛矩阵来判断稳定与否.对极限诱导分岔影响电压稳定进行了机理解释.研究了增大无功源对极限诱导分岔的影响.将提出的判据方法在单机和多机系统上进行了实验,数字仿真算例验证了所提出分析方法和机理解释的正确性和有效性.     

Analysis of control performance for stability robustness of powersystems

This paper presents a novel approach to analyze stability robustness of controls in power systems over a range of operating conditions. The controls considered include exciters, power system stabilizers, and governors. The analytical basis for the approach is presented. The robustness framework for power systems is formulated. Numerical results for a sample test system are obtained and compared with those obtained by conventional techniques     

考虑电压稳定约束的无功规划研究综述

随着电力市场进程的加快,系统运行不断逼近极限,电压稳定已成为影响系统安全的焦点问题,而合理的无功规划对保持系统电压稳定具有重要意义.首先解释了考虑电压稳定约束的无功规划基本概念,接着对目前基于静态和动态电压稳定约束的无功规划模型和求解方法进行总结与评述,提出了该领域需要深入研究的五个关键问题,强调了考虑安全性和经济性的无功规划是当前该领域的发展趋势,最后指出了建立基于动态电压稳定裕度的无功规划模型是避免系统电压崩溃的关键.     

考虑电压稳定约束的无功规划研究综述

随着电力市场进程的加快,系统运行不断逼近极限,电压稳定已成为影响系统安全的焦点问题,而合理的无功规划对保持系统电压稳定具有重要意义。首先解释了考虑电压稳定约束的无功规划基本概念,接着对目前基于静态和动态电压稳定约束的无功规划模型和求解方法进行总结与评述,提出了该领域需要深入研究的五个关键问题,强调了考虑安全性和经济性的无功规划是当前该领域的发展趋势,最后指出了建立基于动态电压稳定裕度的无功规划模型是避免系统电压崩溃的关键。     

考虑双馈异步风电机组无功极限的静态电压稳定概率评估

风电机组中双馈异步发电机(DFIG)恒电压运行时具备一定无功调压能力。为了准确评估含DFIG风电机组的电力系统电压稳定性,得到更为精确的临界功率或负荷裕度的统计信息,构建了考虑DFIG风电机组恒电压运行的无功极限的静态电压稳定概率分析模型,并采用蒙特卡罗法结合内点法加以求解。模型中将风电场接入节点作为PV节点,考虑了风机网侧变换器的注入无功功率,分析了风速随机性和相关性对风电机组注入无功功率和系统电压稳定性的影响。IEEE 118和300节点标准系统的计算结果验证了所提模型和方法的有效性。     

电压下降时同步电动机的动态稳定极限

利用同步电机的状态方程，研究了同步电动机在电压下降时的动态过程。经过多次迭代，分别得到了当电压下降为不同值时，同步电动机保持动态稳定的极限时间；以及不同的机组惯性常数和电机的励磁状态对动态稳定极限时间的影响；最后得出了一些有用的结论。     

电压稳定极限曲面法向量在分布式电源选址中的应用

随着分布式能源在电网中比重加大,合理地选择其安装地点对提高电力系统电压稳定性有重要意义。针对传统的失稳模式参与因子对极限诱导分岔失效的缺陷,提出了一种基于节点注入功率空间的电压稳定极限曲面法向量指标用于分布式电源选址。通过理论分析证明了该指标指导选址的合理性。在IEEE39节点系统测试结果验证了其正确性。与传统方法相比,法向量指标可以较好地处理鞍节点分岔和极限诱导分岔两种主要的失稳模式,具有更大的适用范围。     

Determination of load shedding to provide voltage stability

A computationally simple algorithm is developed for studying the load shedding problem in emergencies where an ac power flow solution cannot be found for the stressed system. The proposed algorithm is divided into two sub-problems: restoring solvability sub-problem and improving voltage stability margin (VSM) sub-problem. Linear optimization (LP)-based optimal power flow (OPF) is applied to solve each sub-problem. In restoring solvability sub-problem, rather than taking restoring power flow solvability as direct objective function, the objective function of maximization of voltage magnitudes of weak buses is employed. In VSM sub-problem, the traditional load shedding objective is extended to incorporate both technical and economic effects of load shedding and the linearized VSM constraint was added into the LP-based OPF. Case studies with a real 682 bus system are presented. The simulation results show that the proposed load shedding algorithm is effective, fast in finding the load shedding scheme to solve the problem of restoring solvability and improving VSM.     

OLTC对含DG电力系统静态电压稳定极限的影响

在静态范围内利用三元分析法阐述了OLTC动作引起的Pmax－、Vcr－曲线的变化,研究了在接入分散,电源的电力系统中,OLTC变比调整对其静态电压稳定极限的影响,并采用两机系统进行了仿真分析得出,OLTC变比变化改变了系统的最大传输功率稳定极限Pmax和临界电压稳定极限Vcr,影响了电力系统稳定运行范围;由于分散电源在配电网的接入,OLTC变比变化对Pmax和Vcr的影响程度不同。     

A robust adaptive voltage and speed regulator for multimachine power systems

In this paper, the transient stability and voltage regulation of multimachine power systems are simultaneously addressed in a multivariable and nonlinear framework. Power systems are nonlinear, large-scale and made of highly coupled generators having a wide range of operating points. Decentralized nonlinear adaptive controllers which continuously update their parameters to compensate for changes in operating points are proposed. The design method is based on a new power system model recently introduced by the authors. The main characteristic of the new model is that interactions between generators and changes in operating conditions are represented by time-varying parameters. The parameters have fixed parts, which depend on the steady-state active and reactive power delivered by each generator, and time-varying parts modelling the interactions between generators, which are treated as disturbances. More importantly, the new model permits the formulation of a control design scheme, which consists of applying the input-output linearization method and stabilizing the resulting partially linear system by a linear control law. The fixed linear gains are computed from an algebraic Riccati equation and considerably attenuate the disturbance effects. An adaptive law derived from the Lyapunov stability method ensures that the controller parameters are bounded and that the generator signals converge asymptotically to steady-state values. The robustness of the controller is used to compensate for the disturbances, while its adaptive nature is used to compensate for load variations that induce operating-point variations. A four-machine power system is used to assess the effectiveness of the multivariable regulator. Simulation results show that good performance in closed loop is achieved.     

电压稳定临界参数的异步接替求取策略

在负荷导纳模型潮流算法基础上.提出了一种基于负荷导纳动态步进的静态电压稳定临界参数的异步接替求取策略.策略1:功率极大值点的快速求取策略.通过跟踪求取逼近过程中的戴维南等值阻抗.并将其对应导纳模值累计于该计算点的负荷导纳值后进行下一次计算,可从初始点快速、不等步地过渡到临界点附近,获得最接近临界点的功率极大值点.策略2...     

N-1故障后系统小干扰电压稳定极限点计算

构建了负荷采用三阶感应电动机并联恒阻抗表示的电力系统短期电压稳定分析数学模型,并推导出负荷增减的表示方法.根据系统小干扰方程状态矩阵特征值为零的特点,提出了计算小干扰电压稳定极限点的数学模型,以求得N-1故障后系统从当前运行状态到电压稳定极限点需增减的负荷.通过对发电机稳态方程中功角的三角函数项引入辅助变量,将极限点计算模型转化为关于未知量的线性或二次函数,进而可采用最优乘子牛顿法计算极限点,以解决极限点处系统稳态方程雅可比矩阵奇异带来的收敛困难.IEEE9节点系统和IEEE39节点系统的计算结果表明该方法能够可靠地收敛到N-1故障后系统的小干扰电压稳定极限点.     

Surge protection of high voltage shunt capacitor banks on AC powersystems survey results and application considerations

A survey of power utilities has been carried out to obtain data on high-voltage shunt capacitor bank surge protection practices which presently exist. The questionnaire sought answers to questions relating to voltage rating, size of bank, number of banks, installation practices, switching arrangements, and the application of surge arresters for overvoltage protection. A summary of the results of the survey is presented along with some general comments and conclusions on the findings. The high rate of return on the survey indicates the widespread interest of utilities in surge arrester protection of high voltage shunt capacitor banks. It does not appear to be common practice among electric utilities to apply surge arresters to shunt capacitor banks for overvoltage protection. Where surge arresters are applied, they are often used to protect other equipment, such as transformers and circuit breakers, against overvoltages during capacitor switching     

Impact of the exciter voltage limit to small signal stability region of a three-bus power system

We investigate the influence of non-differential components to the power system small signal stability region in this paper. A method named unified expression function (UEF) is introduced to describe the piecewise, continuous and non-differential function in the small signal stability study. It converts non-differential points of the original function to poles of the UEF’s derivative function. Then the derivative at those poles can be approximated by UEF’s left-hand or right-hand derivative limits according to the requirement. Based on this method, impact of the exciter voltage limit to power system small signal stability region is then deeply discussed using a simple three-bus power system. We find that the exciter voltage limit can change elements of the system Jacobian matrix so as to cause jump of the system critical eigenvalue. As a result, two new Hopf bifurcation boundaries and a new instability hole emerge in the small signal stability region. When the exciter voltage limit varies, the new instability hole and the new Hopf bifurcation boundaries will change significantly. It makes the topological characteristics of the small signal stability region much more complicated. Since there are many non-differential components in power systems, they should be correctly considered in power system stability studies.