Control of the hybrid modular multilevel converter in motor drive applications

The modular multilevel converter (MMC) has been proved to be potential in medium and high voltage motor drive especially for fan-/blower-like loads. However, the main challenge faced by MMC in the field of motor drive is the large capacitor voltage ripple at low speeds. Currently the mainstream method to eliminate voltage ripple is to inject high frequency components. But it will increase the current stress and bring in the common-mode voltage at the motor terminals. In this paper, a hybrid modular multilevel converter is used in motor drive application to suppress the capacitor voltage ripple, and an operating strategy based on Induction Motor Field Oriented Control (IM FOC) is presented. Lower capacitor voltage ripple and no common-mode voltage can be realized. Full speed range operating of motor driving can also be achieved. Experimental results verify the effectiveness of the strategy.