Highly reliable operation control for MMC-UPFC under unbalanced power grid conditions

The grid contains many negative sequence components under unbalanced conditions, which affect the safe operation of MMC-UPFC. To achieve highly reliable operation control for MMC-UPFC under unbalanced conditions, this paper proposes a decoupling control strategy that introduces the separation of positive and negative sequences. First, the working principles and mathematical model of MMC-UPFC are analyzed. Second, the instantaneous symmetric component method is introduced to separate the positive and negative sequence components of the grid. After that step, dq decoupling control strategies under positive and negative sequences are designed for the shunt side and series side, respectively, which can realize negative sequence compensation and highly reliable operation of MMC-UPFC. Simulation results are presented to verify the effectiveness and feasibility of the proposed control strategy.