电力系统微分代数模型的奇异性和暂态电压稳定

将电力系统微分代数模型的奇异性与暂态电压稳定相联系,用动态负荷模型逼近静态负荷模型,以消除原微分代数方程模型中的奇异性。在2机单负荷3节点系统和新英格兰39节点系统中构造算例,证实了系统在原奇异点附近具有暂态电压崩溃的特征,从而微分代数方程的奇异性可以作为暂态电压崩溃的一种机理解释。此外,还研究了动态负荷模型时间常数、负荷功率和负荷成分对暂态电压稳定性的影响。研究结果表明具有恒功率或恒电流负荷特性且负荷响应较快的系统在重载下易发生电压崩溃。上述结论对研究暂态电压稳定的机理、电压稳定和功角稳定的关系、电力系统微分代数方程模型的理论和仿真分析具有一定的参考价值。     

A generalized approach to the analysis of voltage stability in electric power systems

In this paper a new method for analysing the voltage stability problem in electric power systems is presented. The approach starts with a linearized model in state space form of a multi-machine power system, then rigorous voltage stability conditions are derived on the basis of a suitable aggregated model of the original system capable of retaining the dynamics of voltages at generator and load nodes.The approach allows a systematic individualization of all the dynamic factors which affect voltage instability phenomena and suggests the appropriate representation which has to be adopted for each dynamic component of the system.The validity and usefulness of the suggested method are illustrated by carrying out simulation studies on a sample power system.     

一种模拟负荷动态恢复特性的连续潮流模型

电力系统电压稳定监视与控制需要准确模拟负荷的电压响应特性。负荷在故障后的动态恢复特性是中长期电压失稳或电压崩溃的直接原因。该文提出一种模拟负荷动态恢复特性的连续潮流模型,将负荷功率的时域恢复特性等效转化为负荷静态电压模型中系数的连续变化。文中分别给出ZIP多项式和幂函数2种负荷模型的系数参数化方法,并推导和给出稳定临界点的灵敏度计算公式。负荷恢复型连续潮流可作为一种新的电压失稳故障识别方法。应用该模型在IEEE118节点系统,结果表明负荷恢复型连续潮流可模拟故障后负荷功率的动态恢复过程,识别失稳故障并给出可供预防控制用的灵敏度信息。     

Simulation of load shedding as a corrective action against voltage collapse

The evolution of a lot voltage collapse scenarios on large power systems can be alleviated by controlled load shedding associated with rearrangement of generator outputs. Dynamic simulation of power system mid-term voltage response is required to adequately determine the impact of load shedding actions and to design appropriate control systems. The dynamic simulation must take into account load-voltage behaviour, transformer tap changer controls and limits, generator overexcitation limiters, automatic generation control and system protective devices. This paper demonstrates the impact of load shedding as a corrective action through simulation of the system dynamic response to a disturbance. Whilst load shedding can stabilise a system, rigorous techniques are required to identify the magnitude and location of shedding. The application of voltage modal analysis in combination with the determination of reactive power margins in resolving this problem is demonstrated.     

电力系统动态元件特性对电压稳定极限的影响

电力系统电压稳定性问题本质上属于动态问题,因此分析电压稳定问题必须考虑系统中主要动态元件的特征,文章以简单系统为例通过分析与计算研究了负荷,发电机及其调节系统等动态元件特性对小干扰电压稳定极限的重要影响,说明了基于常规潮流雅可比矩阵奇异性和Ｐ－Ｖ曲线拐点等电压稳定静态分析方法的不严格性。     

基于模糊逻辑的电力系统电压崩溃警报系统

文中建立了一个既考虑静态传输能力极限又考虑动态负荷特性的电压崩溃警报系统,给出不同级别的警报,指出电压崩溃将有可能发生。警报级别越高,电压崩溃发生的可能性越大。系统故障和负荷缓慢增长都可引发电压崩溃,文中针对后者。该系统通过模糊逻辑实现,擅长处理不确定性和非线性问题。考虑了引起电压崩溃的2个主要因素:传输能力极限和负荷动态特性,前者由线路稳定因子LQP表示,后者由dQ/dt和dP/dt指示。经模糊系统得到动态电压稳定指数(DVSI),并划分成不同的警报级别,即电压稳定水平VSL。其可行性和有效性由IEEE 39节点系统验证,动态负荷为电动机。     

A study on voltage collapse mechanism in electric power systems

A mechanism of the dynamic phenomenon of voltage collapse is presented from the physical point of view. It is shown that an iterative reaction of voltage drop between a dynamic load and the system network can cause voltage collapse. The dynamic phenomenon of voltage collapse is analyzed on a simple power system model which includes a synchronous motor. Dynamic equations describing the mechanism of voltage collapse caused by a very small disturbance are derived, and the physical explanation of the voltage collapse mechanism is presented in detail for the case when the system is operating near the bifurcation point and its linearized system matrix has a very small negative eigenvalue. It is shown that an iterative reaction of voltage drop between a dynamic load and the system network can cause voltage collapse     

一种有效的电力系统电压崩溃控制

对于两台发电机母线和一个负荷母线组成的简单电力系统，在负荷母线的无功功率逐渐变化时，会发生亚临界，超临界Hopf分岔和鞍结点分岔，并导致混沌现象和电压崩溃现象，但通过在鞍结分岔平衡点设计的线性状态反馈控制器可以在无功功率的一定范围内消除这些现象，并使系统受扰偏离平衡点后迅速回到平衡点，且该控制器只需用到发电机角速度和负荷母线电压幅值两个状态量，因此，该控制器简单实用，另外对该控制器设计过程中的有关问题进行了讨论，数值仿真说明了该控制器的有效性。     

受端电网静态/动态无功补偿综合优化

提出了一种可同时考虑静态与动态无功补偿的无功补偿优化模型.在对负荷裕度的概率分析的基础上用最小二乘法构造电压崩溃的概率模型.对电压崩溃动态过程进行概率分析,对暂态和稳态过程中对电压稳定和电压质量有所影响的因素进行经济量化,提出了稳态运行费用和暂态运行费用的总和最小为目标函数的无功补偿综合优化模型.在此基础上通过动态仿真与静态分析相结合的方法逐步迭代求解最优补偿容量.华南某电网实际算例中的应用表明,综合无功补偿优化的结果具有最小的年运行费用和最大的故障后负荷裕度,可以显著改善受端系统运行的经济性和安全性.     

电力系统电压稳定性研究综述

对国内、外电压稳定性的研究现状进行了概述,特别介绍了电压失稳现象的根本原因,形成机理,系统动态模型及负荷建模等方面的最新研究成果,还介绍了电压稳定性破坏的防范措施。     

ANALYSIS OF POWER CONVERTER CONTROL USING NEURAL NETWORK AND RULE-BASED METHODS

ABSTRACT

Current-controlled voltage source inverters offer substantial advantages in improving motor system dynamics for high-performance ac drive systems. The controller switches follow a set of reference current waveforms. Fixed-band hysteresis and sinusoidal-band hysteresis controllers have been studied. The first part of this paper develops neural network and fuzzy logic based current-controlled voltage source inverters. The models and learning techniques have been investigated by simulation. The implementation of neural networks is described and simulation results are presented. In the second part of this paper, the new UPS (uninterruptible power supply) with fuzzy logic compensator is proposed. Proposed fuzzy logic compensator is used to prevent voltage drop from nonlinear load. The total harmonic distortion (THD) of proposed scheme is better than that of conventional deadbeat control method for linear and nonlinear load. In the third part of this paper, the application of fuzzy control to DC-DC converters operating at finite switching frequency is studied. Several control methods currently used for buck, boost and buck/boost converters are compared to the fuzzy converter control. Simulation results for several control methods are presented. The simulations show that the fuzzy control method has better dynamic performance and less steady state error.     

Effects of cascaded voltage collapse and protection of many induction machine loads upon load characteristics viewed from bulk transmission system

As is well known, two of the fundamental processes which give rise to voltage collapse in power systems are the on‐load tap changers of transformers and the dynamic characteristics of loads such as induction machines. It is well established that, of these two, the former makes for a slower collapse while the latter makes for a faster collapse. However, in realistic simulations, the load levels of the induction machines are not uniform and it may be expected that some of the loads will collapse first, followed by the collapse of the loads which did not go into instability during the preceding collapses. In such situations, the overall equivalent collapse behavior viewed from the bulk transmission level becomes somewhat different from the simple collapse driven by one aggregated induction machine. This paper studies the process of cascaded voltage collapse among many induction machines by time simulation, in which the load distribution on a feeder line is modeled by several hundred induction machines and static impedance loads. It is shown that in some cases voltage collapse actually cascades among induction machines, with the macroscopic load dynamics viewed from the upper level resulting in a slower collapse than expected from the aggregated load model. We also show the effects of machine protection of induction machines, which results in slower collapse. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(2): 19–27, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20894     

电驱动车辆中发电机与动力电池组的匹配

为了实现电驱动车辆最佳动力性的设计目标,延长发电机和蓄电池的使用寿命,对发电机与蓄电池的匹配进行了研究。通过分析电驱动车辆动力驱动系统的结构特点及功率流控制,对所选发电机进行了负载特性试验,对蓄电池进行了充放电特性试验,在此基础上提出了发电机与动力电池组匹配的原则及计算方法,并在驱动系统的台架试验阶段验证了该方法的正确性和可行性。     

Analytical Comparison of Static and Dynamic Reactive Power Compensation in Isolated Wind–Diesel System Using Dynamic Load Interaction Model

This article presents static and dynamic reactive power compensators together for a self-excited induction generator and synchronous generator based isolated hybrid power system. Reactive power is required for excitation of the induction machine and for load under steady-state and transient state operations in an isolated hybrid power system. For small perturbation of load reactive power and input wind power, the use of a dynamic compensator alone may give better voltage stability but at a high cost; in contrast, the static compensator reduces the cost on compromising with the voltage stability. The proper rating selection of both compensators used may give the optimum solution between the voltage stability as system performance and cost of compensation. The fixed costs and voltage profiles are compared for the different participations of the fixed capacitor bank and STATCOM. The interaction of the dynamic load model is also introduced to make the system more reliable and hence a new power balance equation is derived. A 10% step disturbance in the dynamic load model as well as wind power input is considered for the system study. Four different cases designed for unique participation of static and dynamic reactive power compensators are presented. The analytical comparison is based on cost, rating selection, and voltage stability under transient condition.     

交流输电系统的分岔与仿真研究

为提高系统电压稳定水平,防止电压崩溃事故的发生,基于非线性动力系统的分岔理论,使用通用分岔分析软件AUTO2000对一个典型的3节点系统进行电压稳定的分析,得出了系统在3种不同发电机模型下的分岔点数值。研究发现,不同发电机模型的系统经历的分岔过程不同,说明系统的电压稳定性随着发电机模型的不同而不同。但系统在到达鞍节点分岔前,都因为发生了Hopf分岔而失稳,因此Hopf分岔才是系统失稳的原因。研究还发现跟踪Hopf分岔点开始的极限环曲线可见系统还会经历一系列其它复杂分岔:环面折叠分岔、倍周期分岔和环面分岔;在不同的发电机模型下,系统因为不同的动态分岔点而失稳。时域仿真验证了此结论。     

微机励磁控制系统实时测量技术

介绍了同步发电机微机励磁控制系统基本运行参量的实时测量技术，包括发电机机端电压测量、系统电压测量、有功功率和无功功率测量、励磁电流和励磁电压测量以及发电机频率测量等。所介绍的各种测量技术均经实践考验，特别适用于大、中型同步发电机微机励磁调节器。     

On influence of load modelling for undervoltage load sheddingstudies

This paper explores the influence of load models on decisions of undervoltage load shedding in power systems. A controlled load rejection can be used as an emergency countermeasure to avoid widespread blackout when system voltages are unstable. In this paper, dynamic simulations of a small power system using both static and dynamic load models are presented. When using a static load model, the system includes an explicit model of a transformer with load tap changer. The aim is to demonstrate how different load models influence the analysis and calculation of the amount of load needed to be shed to stabilise the system voltage     

NEURAL NETWORK APPROACH TO DYNAMIC VOLTAGE STABILITY PREDICTION

ABSTRACT

The application of artificial neural network (ANN) on dynamic voltage stability analysis is presented. Two ANN models have been utilized, in which the first ANN model is used to classify the power system as to whether it is dynamically stable or unstable. Then the second ANN model is used for the dynamically stable system to predict the voltage magnitudes at load busbars. Both ANN models are based on the multiperceptron model, and the training is done using the error back propagation scheme. The training set patterns are generated by carrying out dynamic simulations, using induction motor and constant P-Q load models. This paper highlights the method for selection of the optimum number of training sets so as to minimise the time taken in the ANN learning process. The performance of the ANN models have been tested and shown to give good results.     

一种电压薄弱负荷节点群的戴维南等值参数跟踪方法研究

提出了用戴维南等值参数对电压薄弱负荷节点群进行监视的一种方案。静态分析中,采用连续潮流法确定负荷节点电压——负荷参数曲线;在负荷变化率相同情况下,根据电压幅值变化量确定电压薄弱负荷节点;考虑低电压水平与电压崩溃的关系,提出电压幅值变化率作为电压薄弱负荷节点分群所观察信息,考虑地理因素,将电压薄弱负荷节点模糊聚类分群;将每个电压薄弱负荷节点群中典型节点电网侧戴维南等值参数跟踪。提出基于潮流的仿真计算方法进行戴维南等值参数跟踪,观测电压薄弱负荷节点群的电压稳定裕度。该方法在IEEE 118节点系统上验证了其有效性。