Re-synchronization of Distributed Generation based Universal Droop Controller

Abstract-Distributed generation (DG) inverters can operate in the islanded mode and the grid-connected mode. When these DG inverters operate in the islanded mode, they often form a microgrid. The magnitude and phase of the main grid voltage deviate from the microgrid voltage. If the microgrid is connected to the main grid under such condition, it results in a high transient overcurrent which is harmful to the system. This paper presents a new, simple and effective resynchronization mechanism for the universal droop control (UDC) DG inverters to achieve a seamless transfer from the islanded mode to the grid-connected mode. Simulation and experimental results are provided to verify the effectiveness of the proposed method. The result shows that the high transient overcurrent can be avoided and a seamless connection/reconnection to the main grid can be achieved.