Harmonic circulating current injection based power loss optimization control of bottom switch/diodes for modular multilevel converters

Power loss management is one of the most significant challenges for reliability improvement of modular multilevel converters (MMCs). In the MMC, the bottom switch/diode in each submodule (SM) normally takes the maximum power loss. In this paper, a power loss optimization control (PLOC) for MMCs is proposed, where the maximum power losses in the bottom switch/diode of each SM can be effectively reduced through injecting optimum second-order harmonic current into the circulating current of MMCs, and accordingly the reliability of MMCs can be improved by the proposed PLOC. Simulation results with PSCAD software and experimental results with a 1 kW MMC platform are provided to confirm the validity of the proposed PLOC for MMCs.