Low-Frequency Ripple Suppression for Medium-Voltage Drives Using Modular Multilevel Converter With Full-Bridge Submodules

Modular multilevel converters (MMCs) become popular in high-voltage dc transmission systems; however, their applications in medium-voltage (MV) motor drives are still limited due to the technical challenge of low-frequency voltage fluctuation. This paper proposes a new solution to address this problem. Full-bridge submodules (SMs) are used in the place of half-bridge SMs in the MMC to significantly reduce the low-frequency pulsating power in the SM capacitors in startup or low-speed motor drives. Furthermore, quasi-resonant controllers are adopted to acquire improved tracking performance for injected circulating current. Simulation and experimental results are presented and have proved the validity of the proposed method. Comparisons of efficiency and cost between the conventional and the proposed solutions further demonstrate the potential of proposed method for MV drive applications.