A Control Strategy for Star-Channel Modular Multilevel Converter in Variable-Speed Motor Drive Application

Recently, a star-channel modular multilevel converter (MMC) was proposed for zerolow-fundamental-frequency operation. However, it is companied by two potential issues in practices: the star-channel branch suffers from submodule capacitor voltage deviations and the entire-speed-range operation for motor drive is not confirmed. This paper investigates the control degrees of freedom, and proposes control algorithms for star-channel branch and main arms. These control algorithms cascaded with advanced motor controls form the overall control scheme for drive system. Simulation and experimental results show that the star-channel MMC along with the proposed algorithms successfully maintain the SM capacitor voltages, and achieves the variable speed operation from standstill to rated speed.