MMC Coordinated Control Strategy for Maximum Power Output Under Asymmetric Voltage Sag

Aiming at the problems of asymmetric voltage sag on the AC side of flexible DC transmission system, such as the power fluctuation and three-phase current imbalance during the operation of modular multilevel converter (MMC), a MMC coordinated control strategy for maximum power output under asymmetric voltage sag is proposed in this paper. Taking the coordinated control of suppressing the fluctuation of active power and outputting the three-phase balance current as objective, a linear weighted analytical formula is constructed to determine the regulation parameters according to the variation law of the operation characteristics of MMC system with the regulation parameters under asymmetric voltage sag, and then the maximum active power is outputted while ensuring that the outputted peak current of MMC system is within the maximum allowable working range; The proposed strategy not only expands the active power output capacity, but also improves the overall control and protection performance of the system. Finally, the effectiveness of the proposed method is verified through simulation and experiment.