Transient stability simulation of wind generator expressed by two‐mass model

Recently, wind power generation is increasing worldwide. In wind power stations, induction machines are mostly used as generators. Since induction generators have a stability problem similar to the transient stability of synchronous machines, it is important to analyze the transient stability of power systems including wind generators. Although there have been some reports analyzing the transient stability problem, wind turbine and wind generator are, in most cases, modeled as a one‐mass shaft system having total inertia constant. This paper presents simulation analyses of transient stability of power system including induction generator which is expressed by a two‐mass shaft model and analyzes an effect of shaft system modeling on the transient stability characteristics. Simulations are performed by PSCAD/EMTDC in this study. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(3): 27–37, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20394     

基于阻抗法的大规模风电场等值方法研究

大规模风电场的馈入会导致电力系统出现新的振荡稳定性问题。目前,大多数研究都将风电场等效为单个风机进行振荡稳定性分析。然而,该方法忽略了风电场内部的动态交互作用,可能会造成不准确的分析结果。通过矩阵变换,将一个具有M台永磁同步发电机(PMSG)的风电场分解为一个对角矩阵,每个对角矩阵表示等效的PMSG子系统。在此基础上,利用矩阵摄动理论,建立了基于阻抗法的风电场降阶模型,充分考虑了风电场的拓扑结构和内部动态特性。所提出的风场等值方法能够在保证精度的同时很大程度降低解析建模的复杂程度,适用于大规模风电场并网的振荡稳定性分析。通过仿真验证了所提方法的有效性。     

多故障暂态稳定约束最优潮流的轨迹灵敏度法

将暂态稳定约束最优潮流(transient stability constrained optimal power flow,TSC-OPF)计算过程分解为潮流、暂态稳定及轨迹灵敏度、降阶二次规划最优潮流3个子问题的交替求解。在迭代过程中,根据潮流和暂态稳定计算得到状态变量和代数变量时变轨迹;由此判断系统的稳定性,并计算失稳时刻状态变量和初始时刻代数变量对发电机有功和无功功率的轨迹灵敏度;据此将暂态稳定约束最优潮流问题转化以发电机有功和无功功率增量为独立变量的降阶二次规划最优潮流问题;求解这个二次规划模型得到发电机有功和无功功率增量。通过这种交替求解,最终能寻找到满足暂态稳定约束的最优潮流解。以此为基础,提出了不受故障类型和模式影响的多故障处理方法。新英格兰10机39节点和UK 20机100节点系统的计算结果表明,所提方法在计算精度和速度方面具有一定优势。     

考虑暂态稳定的风电穿透功率极限计算模型

为保证风电并网系统的稳定性,建立考虑暂态稳定的模糊随机机会约束规划模型计算风电穿透功率极限。针对风电出力和负荷的不确定性,模型中将两者作为模糊随机变量处理;模型中考虑暂态稳定约束时,根据发电机有功出力和转角的关系,通过时域仿真分析将系统的暂态稳定约束转化为发电机的出力限制约束。采用数学优化方法和时域仿真法相结合来求解所提模型。最后通过在IEEE14节点上仿真分析,证明了暂态稳定约束是风电穿透功率极限的关键约束条件之一。     

Derivation of dynamic equivalents for stability analysis

A method of deriving a reduced-order equivalent model for stability studies of interconnected power systems is presented. Where the system under study is composed of a main system and interconnected subsystems, this method gives an equivalent model to each subsystem with fewer generators, so that, as far as the transient behaviour of the main system is concerned, the computing cost is greatly reduced by using these equivalents instead of the original subsystems.A numerical example applied to a 930 bus and 369 machine system shows that the reduction obtained by this method is quite effective with no loss of response accuracy.     

Method for identifying coherent generators

A method for identifying coherent generators in a power system is presented. The method is based on the property of equal acceleration for coherent machines and requires only the admittance matrix of the system and the moment of inertia of the generators. An expression is developed for the coherency index between any two generators in a power system, and, based on the value of this index, coherency or otherwise of the generators is established. A method of obtaining the dynamic equivalent of a coherent group is also described. The method of coherency identification and equivalencing is illustrated using a 12-machine sample system. The validity of the method is demonstrated by comparing the transient stability study results of the original system with those obtained for the reduced-order model of the system. The proposed method is computationally simple and fast and requires less memory.     

Impact of FACTS controllers on the stability of power systems connected with doubly fed induction generators

The increasing power demand has led to the growth of new technologies that play an integral role in shaping the future energy market. Keeping in view of the environmental constraints, grid connected wind turbines are promising in increasing system reliability. This paper presents the impact of FACTS controllers on the stability of power systems connected with wind energy conversion systems. The wind generator model considered is a variable speed doubly fed induction generator model. The stability assessment is made first for a three phase short circuit without FACTS controllers in the power network and then with the FACTS controllers. The dynamic simulation results yield information on (i) the impact of faults on the performance of induction generators/wind turbines, (ii) transient rating of the FACTS controllers for enhancement of rotor speed stability of induction generators and angle stability of synchronous generators. EUROSTAG is used for executing the dynamic simulations.     

计及风电场集电网络等值模型的仿真研究

以双馈感应发电机组构成的风电场为研究对象,考虑了风力发电机与集电网络的等值,提出两种模型,研究了单机加权等值与等功率损耗结合模型,降阶变尺度等值与并联化结合模型。针对风电场机组参数完全相同的算例,利用PSCAD/EMTDC建立了风电场的不同等值模型,对风速扰动和PCC处发生电压跌落故障下的风电场暂态特性进行了比较分析,研究结果验证了等值模型的正确性。     

Impact of Wind Integration on Transient Voltage Stability in Regional Grid

With the increasing development of wind power,the scale of wind farms and unit capacity of wind turbines are getting larger and larger,and the impact of wind integration on power systems cannot be igno...     

含不同风电机组的风电电网仿真研究

为了研究包含恒速异步风力发电机和双馈异步风力发电机的风电场对电网的影响,应用Matlab 7.0建立了含不同风电机组的风电场动态模型。分析了风电场对电网暂态稳定性的影响,风电机组电压恢复情况,有功、无功变化情况,以及不同风电机组的低电压穿越能力。仿真结果表明：双馈异步风力发电机变速平稳、低电压穿越能力较强,有利于优化电能质量;当电网发生故障时,应针对不同的风电机组采取不同的控制策略以提高电力系统稳定性。     

考虑多控制环耦合的并网逆变器非线性建模及仿真分析

随着新能源发电技术的快速发展和电力电子化设备的规模化应用,电力电子化已成为新型电力系统的重要发展趋势。并网逆变器作为新能源接入电网的重要接口,其暂态稳定性对电力系统的稳定可靠运行尤为重要。并网逆变器具有多控制环耦合与强非线性的特征,因此建立其非线性数学模型是分析其暂态稳定性的重要基础。然而,已有的研究大多是基于小信号建模或只考虑单一控制环节的简化非线性建模,不能完全表征并网逆变器在大扰动条件下的暂态响应。因此,充分考虑并网逆变器多控制环耦合特性,建立其全阶非线性暂态模型,包含功率下垂控制环、锁相环,电压电流双闭环控制。为了便于模型应用,采用奇异摄动法推导了非线性降阶模型。利用Matlab/Simulink时域仿真和RT-Lab实时仿真,验证了全阶模型和降阶模型在小扰动和大扰动下的准确性。在非线性降阶模型的基础上进行线性化,并利用小信号方法分析了系统参数对稳定性的影响。所建立的并网逆变器非线性暂态模型具有较高的模型精度和实用性,可为电力电子化电力系统的暂态稳定性分析提供数学模型基础。     

双馈风力发电机组系统接入与稳定运行仿真

分析了包含大量异步风力发电机组的风电场并网运行后对电力系统静态和动态稳定性的影响。从系统接入和稳定运行的角度研究了双馈风力发电机组及普遍采用的定子磁链定向矢量控制策略在提高风电系统稳定性方面的优势与不足。以实际机组为例在PSCAD/EMTDC平台上建立了仿真模型,结果表明双馈风力发电机组在风速发生变化时不仅能够以变速恒频方式运行并追踪最大风能,且电网电压也比传统鼠笼式风力发电机组更为稳定。在系统发生最严重的三相接地故障时,风电场具有更好的暂态稳定性。     

风电接入对海上油田平台电网稳定性的影响

孤立电网接入风电可以节约燃料,降低运行成本。受风电特性的影响,风电穿透功率使电网在节约燃料的同时,也对电网稳定性造成了很大的影响。文章建立了包括燃气轮机在内的电网模型和多极永磁同步风力发电机模型,评价了由燃气轮发电机供电的海上油田平台孤立电网接入风电时的电网稳定性,并通过仿真研究了该海上油田平台孤立电网接入风电的最大穿透功率。PSCAD/EMTDC的仿真结果和中国海洋石油总公司建造的海上风力发电站的成功并网均表明,文中的平台电网能保持电网频率和负荷电压在规定的范围内。     

基于PSS/E的风电系统暂态仿真研究

大容量风电场的接入对电力系统稳定提出了新的挑战。以GE 1.5 MW双馈感应发电机组成的风电场为研究对象,采用电力系统分析软件PSS/E仿真和分析了风速波动对风电场和系统的影响,比较了风电场和常规电厂对电力系统暂态过程中的不同影响。     

基于小脑模型神经网络-比例积分微分控制的异步风力发电机组软并网控制系统建模与仿真

分析了利用晶闸管进行软并网的原理;采用改进的小脑模型神经网络与比例积分微分并行控制方法对风力发电的异步发电机并网过渡过程进行了研究;利用Matlab/ Simulink平台建立了仿真控制模型。不同风速下风电机切入电网的仿真结果验证了文中所提出控制方案的正确性：采用该控制方案可将并网冲击电流控制在额定电流的2倍以内,且该软并网系统具有较好的稳定性、实时性。     

风电机组对电力系统暂态稳定性影响分析

风电机组作为环境友好型发电的最大来源在电网中的规模日益扩大,必将影响电力系统的稳定性。文章首先对比了恒速异步(CSWT),双馈变速(DFIG)及直驱同步(DDSG)等市场上广为应用的三种风电机组的结构,分析了各个机组的降阶数学模型;通过一款基于Matlab的电力系统分析工具箱PSAT研究了不同故障持续时间下的风电机组暂态稳定性和系统暂态稳定性,对三种机组及其系统的暂态稳定性进行了分析对比;最后讨论了风力发电机组参数对机组暂态稳定性的影响,得知,发电机参数Rr的增加和Xr、Xs的减小有利于恒速风电机组暂态稳定性的提高,Xm、Rs对机组暂态稳定性影响不明显。     

风电场柔性直流输电的故障穿越方法对风电机组的影响

柔性直流输电(VSC-HVDC)系统是大型风电场并网的较好选择,当发生交流系统故障时,故障穿越控制器可维持该系统的稳定性。然而,控制器会对风电机组造成一定影响。针对大型风电场VSC-HVDC系统接入的故障穿越问题,文中首先在PSCAD/EMTDC中建立了含有普通异步/双馈风电场详细模型的两端VSC-HVDC系统仿真模型,并验证了升频法和降压法两种典型的故障穿越方法。然后进一步研究了不同类型风电机组在不同的故障穿越方法下的特性和差异,从而得出风电场VSC-HVDC系统的故障穿越方法对风电机组的影响规律。研究得出的结论可以为不同类型的风电机组接入VSC-HVDC系统时故障穿越方法的选择提供一定的参考依据。     

大容量风电场接入电网的暂态稳定特性和调度对策研究

给出了异步风力发电机组的动态仿真数学模型和含风电场的电力系统暂态稳定分析方法，与国内大型电力系统分析软件相联接，实现了含风电场的电网动态稳定分析及其工程应用。结合风电场接入系统实例，分析了大容量风电场接入系统后电网的暂态稳定特性，提出了保证风电场和电网安全稳定运行的风电场安全容量的概念。探讨了通过控制负荷侧功率因数、采取动态无功补偿装置、加强网架结构、故障 后切除风电机组等措施改善电网暂态稳定水平、提高风电场安全容量的办法。通过计算风电场不同开启容量下最大可调出力及对应风速的关系，提出了风电场接入系统后的电网调度对策，采取该调度策略，可以提高风电场的接入系统容量。     

基于储能的直驱风力发电系统的功率控制

随着风力发电的电网穿透率的增加,风电系统与电网之间的相互影响也越来越大。风电系统输出功率的波动性和间歇性对电网的电能质量及其稳定性将产生较大的影响;与此同时,电网故障也会给风电系统带来一系列的暂态过程,甚至会危及到风电系统的安全运行。本文针对基于储能的并网永磁直驱风力发电系统的运行特点,提出了一种可行的综合控制策略,在使风电系统输出较为平滑的功率的同时,还具有较强的低电压穿越能力,使风电系统基本不受电网故障的影响。仿真结果很好地证明了所提出的控制策略的正确性和有效性。     

Wind turbine Generator modeling and Simulation where rotational speed is the controlled variable

To optimize the power produced in a wind turbine, the speed of the turbine should vary with the wind speed. A simple control method is proposed that will allow an induction machine to run a turbine at its maximum power coefficient. Various types of power control strategies have been suggested for application in variable speed wind turbines. The usual strategy is to control the power or the torque acting on the wind turbine shafts. This paper presents an alternative control strategy, where the rotational speed is the controlled variable. The paper describes a model, which is being developed to simulate the interaction between a wind turbine and the power system. The model is intended to simulate the behavior of the wind turbine using induction generators both during transient grid fault events and during normal operation. Sample simulation results for two induction generators (2/0.5 MW) validate the fundamental issues.