Analysis of Conducted EMI for Sub-Modules in Modular Multilevel Converter

Modular multilevel converter (MMC) is stacked by numerous sub-modules (SMs) which contain many stray capacitances. As a result, the analysis of conducted electromagnetic interference (EMI) is very complicated. In this paper, the SMs in the symmetrical position of the upper and lower bridge arms are regarded as a group, And a conducted EMI model is developed to elaborate the common mode (CM) interference mechanism of each group. Then the CM current components of each group are separated by sweep frequency analysis and source extraction methods. The results are consistent with the theoretical analysis. Accordingly, proper strategies are given to reduce EMI according to the role of different SM group. Finally, the simulation results tested from a MMC grid-connected inverter system are conducted to confirm the validity of the analysis.