A MMC-SST based power quality improvement method for the medium and high voltage distribution network

A modular multilevel converter based solid state transformer (MMC-SST) is proposed in this paper. By adopting the modular multilevel converter as the grid-connected converter at the high voltage (HV) side, the proposed MMC-SST can be applied to the high voltage level, and to comprehensively deal with the power quality problems in the High and medium voltage distribution networks. The topology and the operating characteristics of MMC-SST are analyzed, and the control strategies of the input stage, the isolation stage and the output stage of the MMC-SST are designed separately. A case study is carried out to verify the good performance of the proposed MMC-SST on the power quality improvement of the distribution network.