A Hybrid Nine-arm Modular Multilevel Converter Based on Half-Bridge and Unidirectional Current Full-Bridge Submodules

This paper proposed a novel hybrid nine-arm modular multilevel converter (9A-MMC) based on half-bridge submodule (HBSM) and unidirectional current full-bridge submodule (UC-FBSM). In hybrid 9A-MMC, the UC-FBSMs are employed in middle arms, while HBSMs are employed in upper and lower arms. Compared with conventional full-bridge submodule (FBSM), the number of required semiconductor devices in UC-FBSM is half of conventional FBSM, but the capability of generating negative-voltage is still preserved. The proposed hybrid 9A-MMC can extend the operation range and improve the utilization of dc-side voltage compared with standard 9A-MMC where only HBSMs are used, and this is benefit from the negative-voltage generated by UC-FBSM in middle arm of hybrid 9A-MMC. Besides, the mathematical model of hybrid 9A-MMC is also studied. The operational analyses including the principle of determining the number of SMs in per arm are discussed in this paper as well. Subsequently, the control scheme of hybrid 9A-MMC is presented. Finally, simulation and experimental results are displayed to verify the feasibility and characteristics of the proposed hybrid 9A-MMC.