Shared Capacitor Based Modular Multilevel Converter With Suppressed Capacitor Voltage Fluctuation

The capacitor voltage fluctuation suppression is essential for the reliable and safe operation of the modular multilevel converter (MMC). This article proposes a shared capacitor (SC) based MMC with suppressed capacitor voltage fluctuation, where the SC in each submodule is utilized as the power channel for three phases of the MMC. A multivariate sorting-based voltage balancing control (MVS-VBC) strategy for the SC-MMC is also proposed, which can balance the SC voltages based on the sorting of arm currents and SC voltages. The proposed SC-MMC can effectively suppress the capacitor voltage fluctuation, and accordingly improves the reliability of the SC-MMC. Simulation studies with MATLAB/Simulink are conducted and a down-scale SC-MMC prototype is also built in the laboratory. The results both confirm the effectiveness of the proposed SC-MMC, MVS-VBC strategy, and the capacitor voltage fluctuation suppression effects.