Synchronization Control for Microgrid Seamless Reconnection

In the three-phase distribution network, the microgrid is widely used for increasing reliability and stability of the power grid. The microgrid is a small power grid that can connect to the utility grid via circuit breaker or switch at the point of common coupling (PCC). On standalone mode, the microgrid will supply power to the local loads by itself, and change to provide or consume power from the utility grid on grid-connected mode. However, during transfer from standalone to grid-connected mode, if the microgrid is reconnected without synchronization, the out-of-phase reclosing might be occur. It is a major cause that can affect to the power system due to large inrush current or overvoltage during transition mode. Thus, in order to dispose of this problem, the frequency, phase, and amplitude voltage between two grids need to synchronize before reconnection. In this paper, a synchronization control has been proposed for microgrid seamless reconnection. The additional Distributed Generator (DG) is installed at PCC and assigned to be Dispatch Unit (DU). DU is controlled by Droop Control for generating the electric power to adjust the frequency, phase, and amplitude voltage of the microgrid at PCC during the synchronization process in order to reconnect to the utility grid. The proposed method is performed by eliminating the difference of frequency, phase, and amplitude voltage during transition modes. The simulation has been performed in Matlab/Simulink.