Active power oscillation suppression based on parallel compensation control for grid-tied parallel VSGs system

The virtual synchronous generator (VSG) technique is rapidly developed and widely used due to the weakening of the power grid strength. In order to increase the system capacity and improve the support to power system, the parallel VSGs system receives more attention. However, due to the synchronous generator (SG)-like properties, the active power oscillation is likely to happen in the grid-tied parallel VSGs system when the reference power changes and grid frequency fluctuation happens, which threaten the safe operation of power system. Existing literatures mainly focus on the load change in islanded system, and the grid-tied system composed of parallel VSGs is lack of systematic study. To address this issue, the active power oscillation in the grid-tied parallel system is analyzed and suppressed in this paper. First, a model based on the general current loop is built to describe the interaction effects between parallel VSGs and AC grid. Second, the mechanism of active power oscillation is analyzed by deriving the resonance peak from the model of parallel system. Third, to suppress the active power oscillation and guarantee the frequency stability, a parallel compensation scheme is proposed, which is validated by the simulations and experiments.