Novel submodule voltage balancing topology for hybrid modular multilevel converters

A hybrid modular multilevel converter (HMMC) topology based on a bidirectional diode clamp circuit is proposed in this paper. The proposed topology ensures that the voltages at the ends of the capacitance between the two leads of each sub-module in the same phase are clamped to be equal to each other through the diode clamp circuit. The balancing process through the diode clamp circuit is bidirectional, which is only achieved by the diode clamp circuit. This topology has two advantages when compared with the traditional voltage balance control method. First, the framework used for controlling the entire structure is simplified while the link controlling the voltage balance is eliminated. Second, the control schemes used for the voltage balance are simplified, and the number of the corresponding high-frequency voltage sensors is reduced. Hence, the complexity of the system control is decreased, and communication is realized more easily. When compared with other voltage balancing circuits, the proposed circuit achieves bidirectional equalization and reduces the usage of the inductors. Then, the hardware cost is reduced. Finally, the feasibility of the proposed converter is verified by simulation results given in MATLAB/Simulink.