Evaluation of isolated three-phase AC-DC converter using Modular Multilevel Converter topology

This paper discusses an isolated three-phase AC-DC converter using Modular Multilevel Converter (MMC) topology for a medium voltage application. The MMC at a primary stage of an isolated AC-DC converter directly obtains the high frequency AC voltage from the three-phase AC voltage of the commercial frequency. In addition, the proposed system obtains the low total harmonic distortion (THD) in the input current and maintains the cell capacitor voltage at constant. The comparative evaluations of the system design based on the rated voltage of switching devices are considered. In particular, the numbers of cells and switching devices, the electrostatic energy of the DC capacitors, the THD of the input current and device losses are evaluated when high rated voltage devices: 2.5-kV IGBTs, 3.3-kV IGBTs and 3.3-kV SiC-MOSFETs are applied to the proposed system.