A Dual Modular Multilevel Converter with High-Frequency Circulating Current Injection for MV Open-End Stator Winding Machine Drives

Since its emergence in 2002, the modular multilevel converter (MMC) has been extensively addressed as a promising candidate for medium-voltage machine drives. However, the MMC application as a variable-speed drive experiences a serious challenge pertinent to its unique operating principles, resulting in wide voltage fluctuations across the MMC floating capacitors inversely proportional to the operating frequency. The high-frequency circulating current injection is the mainstream approach to suppress the capacitor voltage ripple at lower operating frequencies, however at the expense of introducing high-frequency common-mode voltage at the machine terminals. This paper adopts the high-frequency circulating current injection approach in a dual MMC topology applicable to open-winding machine drives, with the advantage of mitigating the high-frequency common-mode voltage at the machine terminals by exploiting an inherent feature in open-winding configurations. The theoretical analysis of common-mode voltage mitigation is presented in this paper supported with verification results based on MATLAB simulation.