H-Bridge MMCs with Symmetrical Half-Bridge Submodules

Recently, the announced development of modular multilevel converters (MMCs) advances the field of electric motor drive, high-voltage dc/ac transmission, and renewable generation. In particular, H-bridge MMCs benefit from a symmetrical macroscopic topology, which allows arbitrary voltage inputs/outputs at both terminals as well as bidirectional power flows. However, such flexibility necessitates the bipolar output capability of submodules, thereby excluding conventional unipolar half-bridge submodules. As a solution, this paper proposes H-bridge MMCs with symmetrical half-bridge submodules. As compared to conventional H-bridge submodules, symmetrical half-bridge submodules feature fewer semiconductor devices, reduced costs, and lower conduction losses. The proposed converters are well suited to low-voltage and/or high-current applications, where cost and power loss savings are more pronounced. Further, this paper proposes a voltage balancing scheme that allows sensorless balancing of dc voltages. Finally, simulation and experimental results validate the effectiveness and superiority of the proposed H-bridge MMCs with symmetrical half-bridge submodules.