Improved Modular Multilevel Converter Topology for Low Voltage Variable Speed Drives

Modular Multilevel Converters (MMC) are becoming increasingly popular for HVDC applications and in medium voltage grids and drives. On the contrary, in high-speed low-voltage drives MMCs are typically not considered a good option due to their relatively low power density. In this paper, a new topology is proposed, enhancing the MMC by coupling upper and lower arm sub-modules via Dual Active Bridge (DAB) converters, leading to a sensible reduction of the sub-module capacitance whilst keeping low control complexity. The resulting topology is applied to a high-speed low voltage permanent magnet drive, analyzing the drive startup and its practical operation. Finally, the theoretical claims are validated with simulation results. © 2020 IEEE.