Capacitor Voltage-Balancing Control for Flying-Capacitor MMC without Current Sensors

This paper proposes a submodule (SM) capacitor voltage balancing control scheme for the flying-capacitor modular multilevel converter (FC-MMC), where current sensors are not used. From the SM capacitor voltages and the half-arm insertion index, the DC and AC circulating currents are estimated, instead of measurement. In addition, the half-arm current direction is determined as well. Due to no use of current sensors, the cost of the system is reduced and the communication requirements between the arm controllers and the main controller are decreased. The viability of the proposed voltage-balancing control scheme for the FC-MMC has been verified through simulation and experimental results.