Modeling of D-Q Small-Signal Impedance of Virtual Synchronous Generator

Virtual synchronous generators (VSGs) are widely employed as power sources in three-phase AC power electronic system. In order to analyze the small-signal stability of VSG, it is imperative to construct its analytical model. However, the impedance-based small-signal modeling issue of VSG is seldom discussed in existing works. To fill this gap, this paper conducts a full analytical model for the dq- frame small-signal output impedance of VSG, considering the dynamics of droop mechanism and virtual inertia. The small-signal model of power stage, external power control loop and internal voltage and current controllers are derived successively. Then, the accuracy of the analytical model is validated by measurement results in SABER. Based on the generalized Nyquist Criterion (CNC), the stability of VSG working in grid-connected mode is analyzed using this proposed impedance model. Finally, simulation results verify the analysis.