正阻尼PMSG并网系统限幅间歇饱和引起的次/超同步振荡分析

风电并网所引起的次/超同步振荡研究多集中于小信号模型分析,较少考虑遭受大扰动后限幅等非线性影响。基于单边限幅的描述函数与广义Nyquist判据,对正阻尼直驱式永磁同步发电机(PMSG)限幅环节间歇饱和引起的切换型次/超同步振荡进行分析。首先给出并网PMSG状态空间简化模型并分析其小干扰稳定性;其次发现一种大扰动后并网PMSG因不对称单边d轴电流限幅间歇饱和引起的新型切换型振荡现象;再次结合并网PMSG网侧变流器的频域模型以及单边限幅的描述函数,给出含限幅环节的PMSG系统近似分析模型;最后结合广义Nyquist判据,近似分析不同限幅值和参数下的振荡频率,并解释该种振荡频率随限幅上限降低而增加的现象。     

基于在线辨识的可控串补自适应控制

以三峡-万县500kV线路可控串补(TCSC)工程为背景，以抑制互联系统低频振荡为目的，提出了基于在线辨识的自适应移相式控制器。该控制器采用Prony方法在线辨识主振荡频率，并据此修改相位补偿环节参数，以消除频率变化对控制策略的不利影响，保证输出有适当的相位；在控制器中采用自动增益调节器，可在电力系统大振荡时用大增益控制，以充分发挥TCSC抑制振荡的能力，在振荡减小后则根据在线信息自动降低增益系数。文中对该控制器与固定串补(FSC)进行了比较，比较结果证明其性能优于后者。这表明该控制器对大电网互联系统低频振荡有良好的抑制作用，对运行条件和故障形式有很好的适应性及鲁棒性。控制器达到了系统对稳定性的要求，三一万线系统的仿真研究也验证了这一点。     

Low-order dynamic equivalent estimation of power systems using data of phasor measurement units

This paper utilizes data measured by phasor measurement units (PMUs) to extract a low-order dynamic equivalent model for power system stability studies. The estimated model is a 2-order model for synchronous machines. This model has the advantage of simplicity of classical model and considerably reduces the oversimplifying error of classical model. This method offers an alternative approach to analytical model reduction techniques based on the detailed system models. The proposed method uses the synchronized bus voltage and current phasors measured by PMUs. Using post disturbance data, electrical and mechanical parameters of the equivalent generator are estimated sequentially. Furthermore, a new approach for estimation of two-machine and single machine infinite bus (SMIB) equivalent systems are presented for analysis of electromechanical oscillations. To evaluate the performance of the proposed approach, simulations are performed on a two area 13-bus test system and real measured PMU data. Simulation results show that the estimated model can represent the dynamic behavior of the studied system with good approximation.     

An optimal location of static VAr compensator based on Gramian critical energy for damping oscillations in power systems

The increase in the scale and complexity of interconnected power systems leads to multiple electromechanical oscillations. Therefore, the electric network needs to be made more stable. One type of Flexible alternating current transmission systems (FACTS) devices, namely the static VAr compensator (SVC), can be installed at buses to increase the stability margins and dampen the power system oscillations by exchanging capacitive and/or inductive load to maintain and/or control specific parameters of electrical power systems. The efficiency and performance of the SVC depend on its optimal location. Consequently, seeking the optimal placement for SVC has become a key issue. In this paper, we propose a novel method to find the optimal location for the SVC based on a two‐step approach. First, an energetic approach based on the combination of the controllability Gramian critical energy analysis with the balanced realization reduction technique is used to search for several feasible locations; then the transient stability is analyzed to compare and determine an optimal location through various test cases. The effectiveness of the proposed method has been demonstrated on the IEEE 39‐bus England power system and compared with the modal controllability index. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

PSS就地相位补偿法的模型和理论

为降低稳定器设计在实际大系统中应用的难度和现场调试的困难,提出应用于多机电力系统稳定器设计的就地相位补偿法的模型和理论。在多机电力系统中,首先推导得到稳定器对线路功率振荡贡献的直接阻尼;在此基础上,参照相位补偿的原理,提出稳定器设计的就地相位补偿设计。该方法能够保证稳定器向线路功率振荡提供正阻尼,从而有效抑制系统中的线路功率振荡。而稳定器的就地补偿设计是在附加稳定器的电力装置的局部线性化模型上进行的,无需建立多机电力系统的全系统线性化模型,故而设计简单、实用。     

Identification of the Critical Characteristics of Different Types of Voltage Sags for Synchronous Machine Torque Oscillations

Abstract—This article investigates the effects of symmetrical and unsymmetrical voltage sags on an important characteristic of torque pulsation of synchronous machines. Voltage sags may cause high torque pulsations, which can damage the shaft or equipment connected to it. Duration, magnitude,and initial point-on-wave of the voltage sag are the major characteristics that can influence the synchronous motors torque transients. The effect of the characteristics on the severity of the transient torque is clarified parametrically, and the critical characteristics of each type of voltage sag are extracted. A theoretical analysis is first presented to determine the severest conditions. In this analysis, for each type of voltage sag, the stator flux trajectory in complex coordination is traced to monitor its variation during and after sag. By this method, the effects of different sag types can easily be compared during the sag and at the sag ending instant. To justify the theoretical analysis, simulations of a typical synchronous motor are carried out that confirm the theoretical analysis.     

一起动力站过电压事故的分析

本文通过一起动力站过电压事故原因的调查,得出了两种以上有争议的相近结论.通过分析故障现象、检查结果、以前的试验报告及主要参数,提出了预防同类现象发生的措施及小发电机组的一些主要参数计算应考虑的因素和计算方法.     

扰动观察法能量损耗研究

光伏并网发电系统中,最大功率点跟踪对于提高光伏系统的效率至关重要。详细分析了扰动观察法的振荡、跟踪过程中和误判的能量损耗,并提出一种改进的扰动观察法。仿真和实验证明新方法能很好地解决振荡、跟踪精度和跟踪速度问题。     

基于Matlab的PSS的仿真分析

分析了低频振荡产生的原因以及电力系统稳定器（PSS）对低频振荡的抑制作用。利用Matlab对PSS的参数进行整定,并建立了励磁调节系统仿真模型。用3种运行方式验证电力系统稳定器抑制低频振荡的能力。仿真结果表明：整定后的电力系统稳定器对低频振荡具有良好的抑制作用。     

双馈风电机组附加控制对轴系振荡影响的评估方法

为消除绝对特征值灵敏度指标中参数量纲的影响,同时计及风速的概率分布特性对特征值灵敏度排序的影响,提出了一种累积相对特征值灵敏度(CRES)指标及其计算方法,并基于该指标定量评估了双馈风电机组附加控制(有功功率调制、虚拟惯性控制、下降控制、无功功率调制和机端电压控制)对机组本身轴系振荡阻尼的影响。CRES本质上是相对特征值灵敏度的加权和。通过引入相对特征值灵敏度消除了参数量纲的影响;在此基础上,按照转子运行状态将风速划分为若干区间,以平均风速作为该区间的典型风速,以风速落入该区间的概率作为该区间典型风速下计算所得相对特征值灵敏度的权重。时域仿真结果表明:基于CRES指标能有效地确定不同类型附加控制中影响轴系振荡阻尼的关键参数,通过对关键参数的重新整定可显著减小附加控制器对轴系振荡的不利影响和降低其对传动轴系统的转矩冲击。