基于虚拟稳态同步阻抗的VSG输出阻抗与小信号建模分析

虚拟同步发电机VSG（virtual synchronous generator）由于能够模拟同步发电机的运行特性而受到日益关注。通常而言，VSG通过下垂控制自动独立调节频率和电压，存在有功功率和无功功率易发生耦合振荡等问题，而虚拟稳态同步阻抗方案是一种能够通过调整逆变器输出阻抗特性从而抑制功率耦合振荡的有效方案。首先，介绍了基于虚拟稳态同步阻抗VSG控制策略的基本原理，分析了该方案下的VSG输出阻抗特性，发现该方案下的输出阻抗可由设定的虚拟稳态同步阻抗决定，与逆变器自身的滤波器和闭环控制器等参数无关；然后，通过建立逆变器小信号模型，得出了虚拟稳态同步阻抗可以增加VSG系统低频域特征根阻尼比，有效抑制功率耦合振荡的结论；最后，结合Matlab/Simulink仿真和实验，进一步验证了基于虚拟稳态同步阻抗的VSG控制策略理论分析的正确性。

Modeling and Analysis of VSG Output Impedance and Small-signal Based on Virtual Steady-state Synchronous Impedance

The virtual synchronous generator(VSG) is attracting increasing attention owing to its capability to simu-late the operation characteristics of a synchronous generator. In general, since the VSG automatically adjusts the frequency and voltage independently by the droop control, there exist some problems, e.g., the active and reactive powers are susceptible to coupling oscillations. Note that the virtual steady-state synchronous impedance scheme is capable of adjusting the output impedance characteristics of an inverter, thus it is an effective solution for suppressing the power coupling oscillations. In this paper, the basic principle of VSG control strategy based on the virtual steady-state synchronous impedance was introduced at first, and the VSG output impedance characteristics under this scheme were analyzed. It was found that the output impedance under this scheme can be determined by the preset virtual steady-state synchronous impedance, and it was independent of parameters such as the inverter''s filter and closed-loop controller. Then, by establishing a small-signal model of the inverter, it was concluded that the virtual steady-state synchronous impedance can increase the characteristic root-damping ratio of the VSG system in the low-frequency domain and effectively suppress the power coupling oscillations. Finally, with the combination of simulations using Matlab/Simulink and an experiment, the correctness of the theoretical analysis of VSG control strategy based on virtual steady-state synchronous impedance was verified further.