A Flying Capacitor Hybrid Modular Multilevel Converter With Reduced Number of Submodules and Power Losses

This article presents a novel flying-capacitor-type hybrid modular multilevel converter (FC-HMMC) as an alternative to the traditional modular multilevel converter (MMC) for medium-voltage applications the high-voltage line-frequency switches with the low-voltage high-frequency submodule (SM)-based chain-link, the proposed hybrid solution can balance the benefits of the conventional multilevel converter and the MMC. Compared to the half-bridge MMC, the FC-HMMC can save 50% SMs, 25% devices, 37% capacitor, and 20% conduction losses, hence improving the power density and power efficiency a lot. Besides, the dc and ac sides are not coupled for this topology, which means the modulation index is not fixed. Another advantage is that the high-voltage switch operates in soft switching naturally at any modulation index or power factor, thereby reducing the power losses. Based on this characteristic, a unidirectional FC-type hybrid modular multilevel rectifier with only high-voltage diodes is proposed as well. Finally, the feasibility of the proposed topology is validated by both simulation and experiments.