A novel Modular Multilevel Converter topology with auxiliary voltage clamping circuit for high voltage motor drive

The conventional Modular Multilevel Convertor (MMC) couldn´t operate in low frequency for high voltage motor drive, because of the cell capacitor voltage fluctuation increasing severely with frequency decreasing. This paper presents a new back-to-back topology of MMC with auxiliary voltage clamping circuit for motor drive. The auxiliary circuit use soft-switch strategy to transfer energy between the cell capacitors to balance their voltage. The simulation results show the new MMC topology inverter could keep the capacitor voltage stable in very low frequency operation and could make motor to run from standstill to rated speed smoothly.