Hybrid Modular Multilevel Converter with Reduced Capacitor Voltage Fluctuation

In this paper, a novel hybrid modular multilevel converter (MMC) with reduced capacitor voltage fluctuation is proposed. Compared with traditional MMC based on flying-capacitor submodules (FC-SMs), it replaces the top and bottom FC-SMs with the three-level flying-capacitor converter, and inserts a full-bridge submodule in the ac side. The operating principle and capacitor voltage fluctuation suppression method of hybrid MMC are analyzed in detail, which shows that the hybrid MMC can suppress the voltage fluctuation and eliminate the influence of injecting high-frequency components. Moreover, considering the feature of FC-SM, a novel hybrid capacitor voltage control is proposed, which can reduce the number of PI controllers and sorting complexity. Finally, the accuracy of the proposed topology and corresponding control design is confirmed by simulation results.