Synchronization Process and a Pre-synchronization Method of the Virtual Synchronous Generator

Virtual synchronous generator (VSG) is the concept of controlling the grid-connected inverters to mimic conventional synchronous generators (SGs), and it is considered to be a promising method to enhance the grid inertia and power regulation ability when the renewable energy has a high penetration rate in the grid. In this paper, the power frequency characteristic and the synchronization mechanism of the VSG are analyzed in detail, and a modified pre-synchronization method is proposed. Compared to the existing methods, the proposed method in this paper regulates the VSG frequency by resetting its active power reference according to the local load and eliminates the phase deviation by feedback control of the virtual power, thus the phase angle of the VSG in standalone mode is in accordance with the steady operation point in grid-connected mode and the dynamic power adjustment can be avoided when the VSG connect to the grid. A 30kV A VSG prototype was developed and tested in the laboratory, and the effectiveness of the proposed method is verified with the simulation results based on Matlab/Simulink results based on the VSG prototype.