Frequency Stability Assessment of Grid-forming VSG in Framework of MPME with Feedforward Decoupling Control Strategy

AbstractVirtual synchronous generator (VSG), recognized as a grid-friendly control technique, contributes to providing inertia and damping support from the grid-tied power electronic systems. However, similar to conventional synchronous generator (SG), the VSG is vulnerable to wideband oscillations, and can even become unstable when the system is subjected to a variety of disturbances. To tackle this issue, this paper proposes a magnitude-phase motion equation (MPME) for grid-forming VSG attached to weak grid. Besides, a feedback analytical method is introduced to identify the frequency dynamic stability, judged by the sign of (d/dt)/. Besides, the rate of change of frequency (RoCoF) and frequency nadir (FN) are evaluated by the two indices, i.e., d/dt and . In addition, the relationship between low-inertia-RoCoF-FN-related stability and the weak-damping-oscillation-related stability is illustrated by the feedback analysis. Moreover, in the framework of MPME, a reactive-power feedforward (PPFF) decoupling control strategy is proposed for enhancement of stability and robustness performance of the VSG-system. Finally, the proposed modeling and the reactive-power feedforward decoupling control strategy are demonstrated with the experiments.