A Decoupled Circulating Current Suppressing Strategy For Modular Multilevel Converter

Modular multilevel converters (MMC) have an inevitable double-frequency circulating current between phases because of the three-phase parallel structure. This leads to extra power loss of the converter. The traditional circulating current suppression strategy suppresses the double-frequency content by superimposing the circulating current suppression signal into the reference of upper and lower arms. Due to the addition of the suppression signal, the upper-and lower-arm modulation reference waves are distorted. That affects the quality of output waveform on AC voltage. This paper proposes a decoupled circulating current suppressing strategy which suppresses the circulating current without affecting the output waveform on the AC side. Simulation and experiment results show the effectiveness of the proposed strategy.