Analysis on Circulating Current and Split Capacitor Voltage Balance for Modular Multilevel Converter Based Three-phase Four-wire Split Capacitor DSTATCOM

We propose a modular multilevel converter (MMC) based three-phase four-wire (3P4W) split capacitor distribution static synchronous compensator (DSTATCOM), aiming at compensating unbalanced and reactive load currents. Due to the zero-sequence current compensation, circulating characteristics of 3P4W MMC-DSTATCOM are different from conventional MMCs. Moreover, distinct working principle MMC would affect features voltage. The decoupled positive-, negative- second-order DC components deduced explicitly. Two proportional-integral controllers with dual dq transformation employed suppress positive- negative-sequence current, while quasi proportional-resonance controller is designed eliminate component. Besides, phenomenon voltages revealed, fast-tracking balancing method by controlling flowing through capacitors provided. Digital simulation results verify accuracy analysis feasibility suppression methods.