An Improved Low-Frequency Ripple Suppression Method for Modular Multilevel Converter in Variable-Speed Motor Drive Application

This paper focuses on the application of Modular Multilevel Converter (MMC) in motor drive. In MMC-based drives, the large submodule capacitor voltage ripple at low speed has been a major challenge. An improved voltage ripple suppression method based on the high-frequency common-mode voltage and circulating current injection is proposed, which adjusts the amplitude of the injected voltage and current as the output frequency varies. As a result, the amplitude of the injected circulating current is reduced, leading to better use of injection. The feasibility of the proposed method is validated by the simulation results.