Capacitor voltage balancing and current control method of modular multilevel converter based on generalised averaging approach

To solve the capacitor voltage balancing problem of modular multilevel converter (MMC) under carrier phase-shifted modulation, MMC is modelled by generalised averaging approach. The quantitative relation between the capacitor voltage of submodule and other operating parameters is derived, and the corresponding balancing method is proposed which can make each capacitor voltage to track the reference value. According to the average model of MMC, a current controller is designed, which is suited to the voltage balancing method and can decouple the active and reactive currents. The effectiveness of the voltage balancing method and the current control method is verified by simulation results.