Current control for unbalance capacitors voltage STATCOM

Static compensation (STATCOM) gets more popular as the flexible AC transmission (FACTS) devices increase. The transformerless STATCOM has low cost and concentrates the research interests, however, the capacitors voltage unbalance problem will deteriorate its performance with more harmonics and over current/voltage faults. This paper presented one current control strategy to solve this problem. Firstly, the conventional DC voltage and current loop are implemented with decoupled method to control the active and reactive power for the symmetry system. Secondly, with adjusting the voltage angle, the unbalance phase voltages are impaired. Thirdly, the PWM redundant states replacement method is adopted to avoid the unbalance capacitors voltage in each phase[4], and new current loop to fast the balance process is designed. The simulation results demonstrate that this strategy could suppress the unbalance voltage and provide practicable measures for STATCOM.