摘要: We propose a modular multilevel converter（MMC）based three-phase four-wire（3 P4 W） split capacitor distribution static synchronous compensator（DSTATCOM）, aiming at compensating unbalanced and reactive load currents. Due to the zero-sequence current compensation, the circulating current characteristics of 3 P4 W MMC-DSTATCOM are different from conventional MMCs. Moreover, the distinct working principle of MMC would affect the features of split capacitor voltage. The decoupled positive-, negative-and zero-sequence second-order and DC components of the circulating current are deduced explicitly. Two proportional-integral controllers with dual dq transformation are employed to suppress the positive-and negative-sequence components of second-order circulating current,while quasi proportional-resonance controller is designed to eliminate the zero-sequence component. Besides, the phenomenon of the unbalanced split capacitor voltages is revealed, and fast-tracking balancing method by controlling zero-sequence current flowing through the split capacitors is provided. Digital simulation results verify the accuracy of the analysis and the feasibility of the suppression methods.