Arm inductance selection principle for modular multilevel converters with circulating current suppressing control

With circulating current suppressing control, the dominating second-order circulating current in a modular multilevel converter (MMC) can be effectively decreased, and the arm inductance requirement based on the circulating current is thus largely reduced. This paper investigates the extent to which the arm inductance can be reduced. The circulating current at switching frequency is first explored, which is found to be a limitation for arm inductance selection when the circulating current suppressing control is implemented. The theoretical relationship between switching frequency circulating current and arm inductance is further deduced, and the arm inductance selection principle is proposed. Finally, the theoretical analysis is verified by the experiment.