Low Frequency Oscillation Analysis of VSG Grid-Connected System

Due to that VSG (virtual synchronous generator) simulates the operation characteristics of SG (synchronous generator), similar stability issue that is common in traditional power system may also exist in VSG grid-connected system. In this paper, the low frequency oscillation of VSG is studied, with the influence of reactive power control and dq-axis voltage control considered especially. Firstly, a small signal model of VSG with voltage/current double closed loop control and active/reactive power control is developed. Based on the model, the low frequency oscillation of VSG is explored. It is identified that the low frequency oscillation mode is dominated by virtual rotor motion, which is similar as that in SG. Further, participation factor analysis and parameter sensitivity analysis reveal that the reactive power loop and dq-axis voltage control have much influence on the damping of the low frequency oscillation. Finally, simulated results are presented to verify the analytical results.