考虑频率耦合效应的虚拟同步发电机序阻抗建模

中低压配电网的线路阻抗呈现时变特征，使得基于虚拟同步发电机VSG (virtual synchronous generator)算法的分布式发电单元和电网阻抗产生交互作用，出现系统失稳。阻抗模型是一种基于外特性的建模方法，是研究分布式发电系统稳定性的有效手段之一。考虑到VSG系统存在着频率耦合特性，首先阐述了VSG系统的频率耦合原因,采用谐波线性化的方法建立包含功率外环和频率耦合效应的完整VSG序阻抗模型。再从阻抗测量和并网交互两个角度分析了频率耦合效应对VSG输出阻抗特性的影响。仿真结果验证了模型的准确性和适应性，表明所建立的阻抗模型能准确反映VSG的二倍频频率耦合特征。

Sequence Impedance Modeling of Virtual Synchronous Generator Considering Frequency Coupling Effect

Due to the time-varying characteristics of line impedance of medium- and low-voltage distribution network, interactions exist between the virtual synchronous generator (VSG) algorithm based distributed power generation units and grid impedance, leading to system instability. The impedance model is a modeling method based on external characteristics, which is one of the effective methods to study the stability of distributed power generation systems. Considering the frequency coupling characteristics of a VSG system, the reasons for the frequency coupling of the VSG system are explained at first, and the method of harmonic linearization is used to establish a complete VSG sequence impedance model including the power outer loop and frequency coupling effect. Then, the influences of frequency coupling effect on the output impedance characteristics of VSG are analyzed from the aspects of impedance measurement and grid-connected interaction. Simulation results verify the accuracy and adaptability of the established impedance model, showing that it can accurately reflect the double-frequency frequency coupling characteristics of VSG.