Self-Stability and Induced-Stability Analysis for Frequency and Voltage in Grid-Forming VSG System With Generic Magnitude–Phase Model

The frequency and voltage stability of grid-forming virtual synchronous generator (GFM-VSG) grid-tied system becomes significant in inertia and damping support when GFM-VSG is attached to the power network. In this article, we propose a generic open-loop system model for the frequency–voltage induced-stability analysis, where the dynamics of rate of change of frequency (RoCoF) is a dynamic process that acts on the rate of change of voltage and then, in turn, reacts on RoCoF. In addition, frequency self-stability is evaluated by magnitude–phase feedback analytical model, where the frequency dynamics are identified by the interaction between RoCoF and frequency bias (FB). Also, it is found that inertia is the origin of occurrence of low-frequency oscillation, which induces a natural phase bias between RoCoF and FB. It is found that GFM-VSG can operate stably in weak grid but cannot operate well in ultrastrong grid condition. Finally, theoretical analysis is validated by simulations and experiments.