Contrastive Analysis of Stability of Cascade System With Voltage Source Converter

The DC side voltage stability is a prerequisite for the stability of the cascade system with voltage source converter (VSC). Compared with the small signal analysis method based on the state space model, the small signal analysis method based on the impedance model has a simple modeling process and clear physical meaning. The negative impedance characteristic of the constant power load (CPL) will reduce the effective damping of the system, resulting in system instability. In this paper, two-port small signal models of VSC and CPL are established respectively, and the small signal stability of the VSC and CPL cascade system in strong grid and weak grid is evaluated based on the impedance ratio criterion. In addition, the influence of CPL power and VSC DC side capacitance on the stability of the cascade system is analyzed. According to the stability analysis, the corresponding simulation case is designed to verify the accuracy of the analysis method.