Circulating Current Suppression for Multi-Function Parallel Three-Level Four-leg Converters

The multi-function parallel three-level four-leg converters are proposed for high power applications, which combine grid-connected renewable generation and active power filter (APF). However, the challenge of zero-sequence circulating current (ZSCC) is inevitably. ZSCC takes down the output currents quality and reduces the stability of the system. To suppress ZSCC, the model of ZSCC is established and analyzed in detail. It is revealing that ZSCC is mainly related to zero-sequence duty-cycle difference and benchmark function. Based on the analysis, a PI + feedforward control strategy is proposed to suppress ZSCC. It is realized by adjusting the duty cycle of the redundant vectors in each PWM sampling period. Experimental results verify the effectiveness of the proposed control strategy.