Research on the seamless transfer strategy with real-time phase angle difference adjustment for VSG

With the problem of existing transfer strategy's dependence on grid phase information, an on/off-grid transfer strategy with real-time phase angle difference adjustment was proposed. By calculating the corresponding phase angle difference with the reference power, the phase angle between the inverter output voltage and filter capacitor voltage was adjusted within rather a short time gap, so that the on/off-grid transfer is realized without pre-synchronization. The proposed strategy helps to enhance the control of the grid over the distributed sources, making them serves the grid better. The unified double-loop control was used to avoid instability problem during the transfer process. The simulation model was built to verify the correctness and the reliability of the strategy.