A simplified method for controlling the Modular Multi-level Converter energy based on modified Carrier Phase-Shift Modulation

In Modular Multilevel Converter (MMC), each sub-module requires a voltage control loop for stabilizing capacitors voltage based on the traditional Carrier Phase-Shift Modulation(CPSM), with the number of sub-modules increases, control becomes more and more complex, this article propose a simplified control method to stabilize capacitors voltage based on simplified model of modular multilevel converter and modified Carrier Phase-Shift Modulation, in the simplified model, the upper arm and lower arm can be regarded as one sub-module with high switching frequency. This paper analyses the dynamic model of energy stored in the upper and lower arm, designed the upper and lower arm energy controller to maintain the energy of the upper and lower arm stable. With the modified Carrier Phase-Shift Modulation, the energy can distribute to each submodules without the need the arm current direction. This method solves the drawbacks each sub-module requires a separate voltage controller in the conventional Carrier Phase-Shift Modulation(CPSM), only two controllers is being used in one phase. This method greatly simplify the structure of the control system. Simulation results verify the proposed control method.