Seamless Transfer Control Strategy for Three-phase Inverter in Microgrid

In this paper, a seamless transfer control strategy for three-phase inverter in microgrid is proposed to reduce the impact of grid-injection current during the grid-tied transient period, and to restrain the dc side voltage fluctuation during the islanding transient period. To improve the transient response, a soft-start virtual impedance and single loop current feedback control is proposed to transfer between the islanding mode and the grid-tied mode seamlessly. During the grid-tied transfer transient period, weighted average and phase advance control of the reference output voltage is presented to introduce into power droop control loop, and soft-start virtual impedance and single loop current feedback control is also introduced in order to reduce the impact of the inverter output current and the grid-injection current. Otherwise, while the inverter cuts off the grid, the single loop current feedback control is only introduced to accelerate the discharge of the grid current, and to restrain the dc side voltage fluctuation due to the imbalance of instantaneous current. Simulation and experiments verify the effectiveness of the proposed method.