An improved submodule unified pulse modulation scheme for a hybrid modular multilevel converter

This paper presents an improved submodule unified pulse width modulation (SUPWM) scheme for a hybrid modular multilevel converter (MMC) composed of half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs). The proposed SUPWM scheme can achieve an output voltage of (2N+1) (where N is the number of submodules in each arm) levels, which is the same as that of the carrier-phase-shifted PWM (CPSPWM) scheme. Meanwhile, the proposed SUPWM scheme can alleviate the uneven loss distributions between the left leg and right leg in FBSMs of the hybrid MMC. Moreover, the capacitor voltages of the sub-modules can be well balanced without complicated closed-loop voltage balancing controllers. The validity of the proposed SUPWM scheme is verified by both the simulated and experimental results.