Control strategy for microgrid under three-phase unbalance condition

Microgrid (MG) is generally developed at utility terminal which contains lots of unbalanced loads and distributed generations (DGs). The interaction between MG and the unbalance loads or DGs will degrades the control performance of interfaced inverter in MG and dramatically leads to MG voltage unbalance. In this paper, a negative-sequence compensation based three-phase voltage unified correction strategy is proposed. While MG operates in islanded mode, a positive virtual impedance control is used to eliminate the negative voltage resulted from the negative-sequence current, and then a positive-sequence voltage control loop and negative- sequence control loop are used to improve the inverter control performance. While MG operates in grid-tied mode, the inverter operates as a negative-sequence current source to compensate the negative-sequence currents of loads to guarantee the point of common coupling (PCC) voltage balance. By using the proposed strategy, the voltage control performance of inverter can be improved; the MG power quality can be enhanced significantly. Simulation and experimental results verify the effectiveness of the proposed method.