By setting up a mathematical model of a three-phase three-wire modular multilevel converter (MMC)

the correspondence relationship between the AC side current

circulating current and neutral point potential of DC side and the different components of arm voltages is obtained and the harmonics contained in the above-mentioned electrical quantities in symmetric steady-state are analyzed. A decoupled control method of AC side current

the AC component of circulating current and the neutral point potential of DC side is proposed. Simulation results show that the control method proposed is simple and effective

the decoupled control of AC side current

the AC component of circulating current and the neutral point potential of DC side is verified

and the electrical quantities of different arms remain symmetric

contributing to long-term stable operation of MMC.