Abstract：Modular multilevel converter has emerged as a more viable solution over conventional voltage source converters for applications in high voltage direct current transmission due to its modular structure, which leads to high number of voltage levels resulting in low switching frequency and near sinusoidal voltage waveforms. The traditional full-bridge MMC submodule is able to generate 0、1 voltage levels to the output. This paper proposes a new submodule topologies which can generate 4 voltage levels of 0、1、2、3. Therefore, under the condition that the converter needs to achieve the same level of output, the number of needed submodules on new submodule based MMC is only 2/3 of the half bridge submodule based MMC, which can reduce the size of converter significantly. Meanwhile, the number of IGBT switches is reduced by 1/6 compared to half bridge submodule based MMC system. The nearest level modulation (nearest level, modulation, NLM) and modified voltage balancing algorithm is proposed for the new topology and is validated by Matlab/Simulink simulations. The validate of the new submodule and the proposed method is verified by simulation results.
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2017, Vol. 18 
