Output Impedance Modeling and Parameter Disturbance Stability Analysis of Photovoltaic Virtual Synchronous Generator

This paper studies the stability of grid-forming inverter under strong and weak grid when the control parameters of virtual synchronous generator (VSG) are changed. Based on the influence of filter parameters, voltage and current double closed-loop parameters and other factors, the output impedance model of virtual synchronous generator in d-q rotating coordinate system was established by small signal analysis method, and its analytical expression was derived. The Bode diagram of output impedance was used to compare and analyze its influence on the impedance characteristics of various frequency bands and the stability of grid connection. Short-circuit ratio (SCR) definition is used to simulate strong and weak grid characteristics by changing the inductance of the grid line, and to change the output impedance by changing the key parameters of VSG control. Finally, the conclusion that the virtual synchronous machine is easy to lose stability in weak grid is verified by simulation.