Abstract: In order to solve the problem that it is difficult to determine the adjustment parameters in the multi-objective protection control, this paper introduces the weight factors of active power fluctuation and AC current fluctuation, and constructs a linear weight expression. In order to obtain the optimal weight factor, this paper analyzes in depth the restrictions of modular multilevel converter(MMC)system safe operation conditions on weight selection,establishes a weight optimization selection model. Based on the above analysis, this paper proposes a multi-objective coordinated control strategy for MMC, which aims to suppress active power fluctuations and coordinate the imbalance of AC current. The strategy considers the maximum allowable current of the system and the maximum allowable voltage fluctuation of the bridge arm capacitor, and does not require additional control elements to suppress overcurrent and bridge arm voltage overvoltage. The simulation experiment demonstrates the feasibility and effectiveness of the proposed strategy.

Key words: modular multilevel converter, AC side asymmetric fault, coordination control, power fluctuation, asymmetric three-phase current