Impact of the Leakage Inductance on the Reflected Wave Phenomenon in MMC based Motor Drives

With a growing number of silicon carbide (SiC) devices used in the modular multilevel converter (MMC) based medium voltage motor drive systems, the reflected wave phenomenon (RWP) under high dv/dt needs to be studied. In this paper, the voltage reflection in the MMC based motor drives is analyzed with a focus on the impact of the leakage inductance of the arm inductors. A seven-level MMC built with 1.7 kV SiC MOSFETs is modeled and simulated. The simulation results show that the leakage inductance of the arm inductors helps reduce the dv/dt at the MMC output but increases the voltage stress on the arm inductor windings and the load. A simple method is proposed to mitigate dv/dt and voltage overshoots applied to the machine windings. Presented simulation and experimental results validate the proposed method.