Enhanced Hybrid Modular Multilevel Converter With Improved Reliability and Performance Characteristics

This paper proposes an enhanced hybrid modular multilevel converter (MMC), which utilizes a combination of half-bridge submodules (HBSM) and at least one full-bridge submodule (FBSM). In the proposed structure, FBSMs work with half of the HBSMs nominal voltage in each arm. Due to the presence of FBSMs, HBSMs switching frequency drops significantly, which reduces the converter power loss compared to half-bridge based MMCs. Furthermore, because of redundant FBSMs, (2N + 1)-modulation can be employed to generate the output voltage without increasing the circulating current, thus, the converter performance is improved notably. Besides, with the redundant FBSMs, the converter can continue its operation even if a fault occurs in one of HBSM switches. All the control procedure is accomplished using model predictive control strategy and performance of the proposed converter is verified by several simulation and experimental studies. The obtained results confirm the feasibility of the proposed scheme in reducing the converter loss, improving its performance and fault-tolerant operation.