LAUSR

The proportional-integral multi-resonance repetitive controller (PIMR-RC) can track the reference current signal of the grid-connected inverter without static error, suppress low-frequency harmonic disturbance signals, and have a fast dynamic response. However, when the grid frequency fluctuates, the performance of reference signal tracking and harmonic suppression will decrease. Based on PIMR-RC, this paper proposes a novel fractional-order repetitive controller (NFO-RC) based on the Thiran infinite impulse response (Thiran IIR) filter, which can automatically track the change of grid frequency. Firstly, the frequency domain analysis of PIMR-RC is given. Then, the realization method based on the Thiran IIR filter is designed, and the structure of NFO-RC system is presented. Moreover, the stability and harmonic suppression analysis of NFO-RC system based on Thiran IIR filter are given. Finally, experimental results on a single-phase LCL grid-connected inverter verify the excellent harmonic suppression performance of the proposed NFO-RC system under grid frequency fluctuations.