改进下垂控制的并联逆变器小信号稳定性分析

由传统下垂控制方式构成的逆变器并联系统在受扰动时易产生振荡,当负荷发生剧烈变化时,系统的稳定性易受影响。在功率计算环节引入的低通滤波器会增大系统惯性的同时也会延缓系统响应速度。本文在传统控制方式上加入以下两项来改善效果,即功率微分项和一次函数项(功率与下垂控制系数的一次函数项)。功率微分项能明显提高系统的稳定运行性能和动态响应性能,一次函数项能有效实现下垂系数随功率变化自适应调节。     

Compensation of droop control using common load condition in DC microgrids to improve voltage regulation and load sharing

DC microgrid is one feasible and effective solution to integrate renewable energy resources, as well as to supply reliable electricity. The control objective of DC microgrids is to obtain system stability, low voltage regulation and equal load sharing in per unit. The droop control is an effectively method adopted to implement the control of microgrids with multiple distributed energy units. However in the application of low-voltage DC microgrids, the nominal reference mismatch and unequal cable resistances require a trade-off to be made between voltage regulation and load sharing. In this paper, a unified compensation framework is proposed using the common load condition in local controller, to compensate the voltage drop and load sharing errors. The voltage deviation is compensated with a P controller while the load sharing is compensated through a PI controller. An additional low bandwidth communication is introduced to share the output current information, and the average output current in per unit is generated to represent the common load condition. The performance of the proposed method is analyzed and compared with basic droop control and hierarchical structure method. The large signal stability is analyzed to define the margin of compensation coefficients. Simulations and experiments are carried out to verify the performance of the proposed method.     

基于局部电压稳定指标的裕度灵敏度分析及应用

提出一种基于局部电压稳定指标的裕度灵敏度分析新方法。以局部电压稳定指标为基础推导出负荷节点电压稳定裕度,该裕度具有确定的上、下界,且不受负荷增长方式影响;利用负荷节点电压稳定裕度有效识别了系统电压弱节点和弱节点集合;定义局部电压稳定指标的裕度灵敏度,确定与弱节点集合强相关的负荷节点,分析弱节点集合邻域节点无功波动对弱节点集合电压影响程度;最后将所提方法应用于系统无功补偿装置配置中,典型系统的仿真结果证明了所提方法的可行性和有效性。     

基于小交流信号注入的接口变换器二次控制方法

在交直流混合微网中,双向接口变换器是连接交流子网和直流子网的桥梁,对系统的安全稳定运行和功率的合理分配起着举足轻重的作用。目前,双向下垂控制方法广泛用于双向接口变换器的控制中,它是通过检测直流母线侧电压和交流母线侧频率来反映直流子网和交流子网的功率需求,进而控制功率的流动。然而,这种方法会使变换器输出的电压和频率存在偏差,同时,在实际中,每个变换器的参数和输出阻抗也不会完全相同,这也会造成功率在并联变换器之间分配不精确。为了解决以上问题,以双向下垂控制为基础,提出了小交流信号注入的新型二次控制方法,在该方法中小交流信号在并联的各变换器之间如同一种通讯信号,其频率和接口变换器输出基波电压的下垂偏置成下垂关系。该方法可以使变换器输出的电压和频率恢复到额定值,同时,可以使并联变换器之间的功率精确分配。matlab/simulink仿真结果验证了所提控制方法的有效性。     

电力系统概率小扰动稳定性研究进展

随着电力系统新能源渗透率的不断增大,考虑到新能源具有随机性强、波动性大等特征,会对高渗透率的新能源电力系统小扰动稳定性产生影响,从而制约电力系统的发展。为此,文章着重针对小扰动的来源、对电力系统的影响以及分析方法进行了总结归纳,首先简要介绍了小扰动的相关概念,后从风电等不确定新能源发电、电动汽车等新型负荷接入电网以及网络安全三方面阐述了各自对电力系统的影响,并对小扰动分析方法进行归类,分析了蒙特卡洛法(MCM)、随机响应面法(SRSM)和概率分配法(PCM)的相关原理以及研究现状。最后介绍了现阶段小扰动的抑制措施并提出了对未来电网发展方向的一些思考。     

用特征值灵敏度法分析系统参数对小干扰稳定性的影响

电力系统小干扰分析中,特征值对参数的灵敏度定量地提供了参数影响的程度和趋势。该文以某电网的典型运行方式为基础,根据特征值对任意运行参数(如PQ节点功率、PV节点电压)和网络参数(如线路阻抗、变压器分接头)的灵敏度,分析了各个系统参数对电网小干扰稳定性的影响。依据分析结果,可以通过调整系统参数来改善系统的小干扰稳定性。     

平均成本下垂控制策略在分布式发电中的应用

提出了一种线性分布式电源功率分配方案,在微电网孤网运行时可节约总的发电成本。基于(分布式电源)各自的平均发电成本,通过调整分布式电源下垂率实现成本的节约。与现有的基于非线性成本下垂策略相比,所提方案使用下垂曲线,在减少总成本方面取得了良好的性能。该方案以可调度及不可调度下垂控制的分布式电源微网进行了实验。实验结果证明了在不同的运行情况下,所提方案具有高效和良好的特性。     

基于负荷裕度的在线电压稳定指标

提出了一种基于PMU同步测量数据的负荷节点有功极限和无功极限快速计算方法,在此基础上分别给出电压崩渍的有功裕度指标和无功裕度指标.该方法基于系统的当前运行点,采用π型电路模型对复杂网络进行在线参数辨识,在此基础上推导了负荷的有功裕度和无功裕度的快速计算方法,然后采用基于节点功率的电压稳定指标进行电压稳定判别.该方法能明确区分是由于有功过载还是无功缺乏所引起的电压失稳,并且具有良好的单调性和线性,能够为电压稳定的在线控制提供准确的参考依据.在IEEE 118节点系统中的仿真证明了该方法的有效性.     

基于多智能体一致性的微电网自适应下垂控制策略

利用智能体间的分布式通信,提出了一种基于多智能体一致性的自适应下垂控制策略,用于解决传统下垂控制中频率和电压偏差、系统稳定性和功率分配精度的问题。在传统下垂控制基础上,建立了有功功率分配、有功-频率和无功-电压的二阶动态模型。在考虑通信延迟的基础上,利用无领导的一致性控制分布式电源的有功出力满足传统下垂控制的要求;利用含虚拟领导者的一致性修正传统下垂控制中的频率和电压偏差;通过Lyapunov直接法验证了系统的渐进稳定性,故而解决了传统控制中有功下垂系数对系统稳定性的影响问题;分析了通信扰动对控制结果和稳定性的影响。通过仿真验证了所提策略的有效性。     

基于连续潮流模型的直流配电网负荷裕度分析

直流配电网由于能灵活接纳分布式电源和直流负荷,是未来智能配电网的发展趋势。随着直流配电网中负荷需求的不断增加,系统会由于静态电压失稳而崩溃。因此,研究直流配电网的负荷裕度对保障系统安全可靠运行至关重要。该文首先建立直流配电网的潮流模型,并将含双有源桥DC-DC变换器的潮流模型嵌入到直流配电网潮流模型中,提出了基于连续潮流法的直流配电网负荷裕度计算方法。通过两类典型的拓扑结构的直流配电网仿真,结果表明直流配电网在减小网络损耗和提高供电能力方面明显优于交流配电网,而且DC-DC变换器变比增加有助于负荷裕度提升。     

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.     

Transient stability output margin estimation based on the energy function method

In this paper, a new method of estimating the critical generation margin (CGM) in power systems is proposed based on transient stability diagnostics. The proposed method can directly compute the stability limit output for a given fault based on the transient energy function method (TEF). Since CGM can be directly obtained by the limit output using estimated P‐θ curves and is easy to understand, it is more useful than the conventional critical clearing time (CCT) of the energy function method. The proposed method can also estimate CGM as a negative value, which means instability in the present load profile, and so a negative CGM can be directly used as a restriction on generator output. The accuracy and fast solution ability of the proposed method are verified by applying it to a simple 3‐machine model and IEEJ EAST10‐machine standard model. Furthermore, the usefulness of the method for severity ranking of transient stability for various fault cases is discussed by using CGM. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 10–19, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.21035     

基于附加电量的直流微电网动态稳定控制策略

直流微电网的低惯性问题以及遭受扰动后分布式电源与负荷短时保持功率恒定引入的负阻尼,均会削弱直流电压的动态稳定性.对此深入探讨了直流微电网的动态稳定机理,从电量的角度赋予系统稳定判据物理意义.首先基于直流微电网的伏安特性,分析系统运行点的移动轨迹与稳定运行约束条件.其次,基于直流微电网的状态方程,推导系统的电量模型,分析各端换流器具备的暂态电量对系统稳定运行的影响机理,并结合稳定运行条件,提出基于附加电量的直流微电网的动态稳定裕度及判据.然后,基于直流微电网的动态稳定裕度,通过改进储能侧换流器的电压下垂控制,提出基于附加电量的直流微电网电压动态稳定控制策略,并分析其对直流电压暂态过程的影响.最后,搭建多端直流微电网仿真系统,验证所提电压动态稳定判据的正确性,以及附加电量对直流微电网动态稳定的支持能力.     

Capability curve based enhanced reactive power control strategy for stability enhancement and network voltage management

Reactive power has become a vital resource in modern electricity networks due to increased penetration of distributed generation. This paper examines the extended reactive power capability of DFIGs to improve network stability and capability to manage network voltage profile during transient faults and dynamic operating conditions. A coordinated reactive power controller is designed by considering the reactive power capabilities of the rotor-side converter (RSC) and the grid-side converter (GSC) of the DFIG in order to maximise the reactive power support from DFIGs. The study has illustrated that, a significant reactive power contribution can be obtained from partially loaded DFIG wind farms for stability enhancement by using the proposed capability curve based reactive power controller; hence DFIG wind farms can function as vital dynamic reactive power resources for power utilities without commissioning additional dynamic reactive power devices. Several network adaptive droop control schemes are also proposed for network voltage management and their performance has been investigated during variable wind conditions. Furthermore, the influence of reactive power capability on network adaptive droop control strategies has been investigated and it has also been shown that enhanced reactive power capability of DFIGs can substantially improve the voltage control performance.     

基于I-V下垂控制的直流微电网动态特性分析与改善

本文对孤立直流微电网动态特性进行了分析,并提出了改善策略.在孤网条件下,电压主要靠系统中基于储能的DC/DC变换器进行控制,因此多DC/DC变换器动态特性即可反应系统全局的动态特性.本文中各DC/DC变换器采用I-V下垂控制,并以负载的变化量为输入,变换器输出电流、占空比及母线电压为状态变量对多DC/DC变换器进行了大信号模型的建立.基于上述模型,本文对输出电流动态特性的影响因素进行了根轨迹分析,最后提出自适应P控制策略以提高直流微电网中的动态特性.最后通过仿真对提出的模型及控制策略进行了验证.     

基于二次锥优化的辐射状配电网静态电压稳定裕度计算

负荷裕度计算是评估配电网静态电压稳定性的有效手段。结合辐射状配电网的特点,提出了基于二次锥优化方法的负荷裕度计算方法。在建立含DG辐射状配电网负荷裕度计算数学模型的基础上,通过变量代换将该模型向锥优化标准形式转化,实现负荷裕度优化模型的快速计算。以IEEE-33节点系统作为算例,将二次锥优化方法与传统连续潮流法比较,验证了负荷裕度的二次锥优化模型的正确性以及二次锥优化方法的高效性。     

注入功率空间上电力系统小扰动稳定域的实用边界

基于注入功率空间上小扰动稳定域的定义,提出了多机电力系统小扰动稳定域的实用边界计算方法.首先分析了二机电力系统小扰动稳定域的特点,发现其边界具有固定的规则形状;然后,引入分群和二机等值的方法,对多机系统先分群和等值,再搜索Hopf分岔集.由于全部分群子空间上的Hopf分岔集和原系统的Hopf分岔具有映射关系,所以等值简...     

基于奇异熵TLS-ESPRIT算法的微电网小信号稳定性分析

针对微电网的小信号稳定性进行了研究。基于奇异熵和TLS-ESPRIT算法,提出了一种能直接从微电网运行数据中提取其小信号稳定模态的方法。该方法利用有效信号和噪声在奇异熵方面的显著差异来准确识别信号模态的阶数,有效抑制噪声干扰,并利用TLS-ESPRIT算法精确提取信号模态信息。仿真结果表明,所提方法较传统的Prony算法在计算复杂度和精度方面都具有明显的优势,且该方法能有效识别微电网在并网或孤网运行模式下的小信号稳定模态。     

风电场小干扰稳定研究

为了降低风电场并入电网对电力系统的小干扰稳定可能带来的影响,建立了双馈感应发电机数学模型和桨距角控制模型,根据小干扰稳定理论,在PSAT平台上对风电场接入一个单机无穷大系统和WSCC 3机9节点系统进行特征值计算和小干扰稳定分析。仿真算例分析结果表明,与风电机组强相关的振荡模式阻尼特性良好,系统振荡稳定。