A Six-Arm Symmetrical Six-Phase Hybrid Modular Multilevel Converter with Unidirectional Current Full-Bridge Submodules

Abstract

Multiphase converter complexity is one of the concerns that restrict the widespread utilization of multiphase machines. One of the developmental trends to alleviate the converter complexity is reducing passive and active component counts. In this regard, several examples have been reported in the literature for modular multilevel converter (MMC) topologies with a reduced component count for six-phase medium-voltage motor drives. A three-leg nine-arm MMC (9A-MMC) with half-bridge submodules has been proposed with a 25% reduction in the number of employed components, compared to the standard six-leg twelve-arm MMC, however with limited output voltage magnitude. To enhance the dc-link voltage utilization, hybrid designs of the 9A-MMC have been recently suggested with a combination of half-bridge and bidirectional/unidirectional current full-bridge submodules (FB-SMs) in each leg. For further structural reduction, this article proposes a two-leg six-arm hybrid MMC with half-bridge and unidirectional current FB-SMs for symmetrical six-phase machines. The proposed architecture achieves a further reduction in component count, reducing the implementation complexity without compromising the delivered power. Detailed illustrations, analysis, and operational concepts of the proposed topology are presented. To quantify its pros and cons, the proposed topology is assessed versus other existing alternatives in the literature. Simulation and experimental results are presented to validate the concept and effectiveness of the proposed architecture.