A circulating current suppressing control in modular multilevel converter based unified power quality conditioner

In this paper, a circulating current suppressing control is proposed to suppress the circulating current in the modular multilevel converter based unified power quality conditioner (MMC-UPQC). In order to decrease the circulating current among the six phases of MMC-UPQC, which is resulted from the voltage difference of the six phases, an averaged phase voltage control is introduced in the UPQC control strategy. Operating principle of the proposed control is discussed. Simulation results are presented to verify the effectiveness of the proposed control method.