Abstract
High-power converters operate at low carrier ratios featuring significant digital delay, making it hard to suppress negative sequence current under unbalanced voltage while keeping the system stable. To solve this problem, the worse amplification effect from negative sequence disturbance to negative sequence current due to low carrier ratios under conventional proportional-integral (PI) control is first pointed out in this paper, and the amplification factor is further quantitatively explained with bilateral frequency domain analysis using the complex transfer function. Moreover, a phase-corrected proportional resonant (PR) controller is proposed in this paper to address this negative effect. Under unbalanced conditions, the newly added pole at negative fundamental frequency may regulate the negative sequence current without steady-state error. Besides, a global bilateral phase correction (BPC) and a local phase correction (LPC) are also presented to ensure stability under low carrier ratio operation. Finally, the experimental results are provided to demonstrate the theoretical analysis.
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