Parameter Robustness Improvement for Repetitive Control in Grid-Tied Inverters Using an IIR Filter

In this article, the stability robustness of repetitive control (RC) in the grid-tied inverter is discussed. Due to the limited control band, high-frequency characteristics of the control plant are seriously affected by the modeling and parameter uncertainties, which can lead to RC controller instability. Then, an infinite impulse response (IIR) low-pass filter is applied inside the internal model of RC to improve the stability robustness. To alleviate the effects of the RC gain reduction induced by the phase lag of the IIR filter, an approximated simple computational method of the phase compensation is proposed. The situation of the gain attenuation and frequency deviation of RC caused by the IIR filter is analyzed, and a method that modifies the phase compensator in real time for the IIR filter is applied to resist the grid frequency variation. Parameter design is provided in details, and comparison experiments are performed in different uncertainty situations to demonstrate the effectiveness of the proposed approach.