An improved modular multilevel converter with DC fault blocking capability

In contrast to the conventional half-bridge based MMC (HB-MMC), the full-bridge based MMC (FB-MMC) has the advantage of dc fault blocking capacity, but at the costs of increased power semiconductor devices and power losses. This paper proposes a hybrid modular multilevel converters (MMC) comprising of half half-bridge and half full-bridge sub-modules. The proposed topology takes the advantages of dc fault blocking capability of FB-MMC with less semiconductor devices and lower power losses than the FB-MMC. Comparative studies on power losses for different circuit configuration are conducted. Detailed pre-charge scheme for the proposed Hybrid MMC are designed and verified by simulations. Experiment results are provided to demonstrate the feasibility and validity of the proposed Hybrid MMC under normal operation and dc fault condition.