A Power Loss Optimization Method for Modular Multilevel Converters Based on Variable Control Cycle

The modular multilevel converter (MMC) can be used in lots of applications. Several researches pay attention to reducing power loss of switching device. However, few have studied the loss optimization of MMC when the actual power is less than the rated power and capacitor voltage fluctuations of submodule (SM) are relatively small. This paper analyzes the performance in details of the MMC in this condition. And then, a loss optimization method based on variable control cycle (VCC) is proposed, which increases the control cycle of the capacitor voltage balance method as well as keeps the capacitor voltage fluctuate within limits to reduce the average switching frequency and average switching loss of SMs. The simulation result confirms the feasibility of method in this paper.