Implicit Sequence Impedance Model and Improved Virtual Impedance Design Method for Grid Forming Converters

Abstract

The control of virtual synchronous generator (VSG) has been widely used because it can improve the stability of the grid connection of new energy. The analysis of its grid connection stability and performance improvement have also become research hot spot. Firstly, in this paper, considering the influence of the VSG voltage and current double closed-loop comprehensively, an implicit grid-forming sequence impedance model were proposed. Secondly, the output impedance characteristics of VSG before and after the improvement were compared and analyzed. The influence of different system parameters on the system stability were systematically analyzed.Based on the theoretical analysis results, an improved design method of virtual impedance was proposed to improve the stability of the system. Finally, the validity of the theoretical analysis was verified through experiments.

Keywords: Distributed energy sourse, VSG, Converter stability analysis, Sequence impedance model, Virtual impedance