Reduced loss modulation based capacitor voltage non-sorting balancing control for full-bridge MMC

From the perspective of reduced loss modulation, the concepts of essential and additional switching actions are presented, and a capacitor voltage non-sorting balancing control is proposed on this basis. The relevance among the operation modes, switching action modes and the losses are analyzed, such as the conduction loss, essential and additional switch losses of full-bridge modular multilevel converter (MMC). Combining with loss relevance and the principle of as low as possible of capacitor voltage fluctuation, the criteria to choose and judge essential and additional switch action modes are specified. Finally, two capacitor voltage non-sorting balancing control strategies for full-bridge MMC are given. Through the PSCAD/EMTDC based simulation, it is validated that the proposed control strategy can meet the demand of static and dynamic operation of HVDC power transmission system, and the switching frequency can be significantly reduced.