Phase-Based Fractional-Order Repetitive Control for Single-Phase Grid-Tied Inverters

A novel fractional-order repetitive control based on phase angle information interpolation is proposed for single-phase LCL-type inverters in this paper. Conventional fractional-order repetitive control typically relies on inaccurate grid frequency information detected by a phase-locked loop or the frequency-locked loop, which may result in a potential degradation in harmonics suppression capability. To address this issue, phase information is investigated to implement the fractional order of the repetitive controller through the linear interpolation method. A major advantage of the proposed scheme lies in that it avoids explicit frequency calculation and reduces sensitivity to frequency estimation fluctuations compared with conventional fractional-order repetitive control, enhancing its frequency adaptability. The stability analysis and the design process for the proposed scheme based on a plug-in-type repetitive control are given. Experimental results support the efficacy and advantages of the proposed control strategy.