A Supervised Capacitor Voltage Balancing Method of Modular Multilevel DC/DC Converters for Medium Voltage DC Application

In this paper, the submodule capacitor voltage fluctuation of high-frequency modular multilevel dc-dc (MMDC) converters is investigated firstly. Considering the high switching frequency and the control delay in practice, the issue of large capacitor voltage ripple in MMDC converters is revealed. Then a supervised capacitor voltage balancing method is proposed in this paper. This balancing method can avoid the continuous charging of submodule capacitors, which can reduce the voltage ripple by 61%. Finally, the theoretical analysis and proposed method is validated on a 16kV MMDC prototype.