Analysis of Common Mode Voltage and Current in MMC Flexible DC System with AC Side Grounding Method

Employing the third harmonic injection modulation method can improve the DC voltage utilization rate for MMC. The third harmonic injection will generate the third common-mode voltage at the DC side of the MMC-based DC distribution network. This paper analyzes the MMC of three harmonic voltage. A common-mode equivalent network model of a multi-terminal DC distribution network is established. When the neutral grounding mode on ac side is adopted in the multi-terminal DC distribution network, the equation between neutral grounding impedance and common-mode current and voltage is derived. Finally, it is verified on the PSCAD simulation program.