Second‐order RC: analysis, augmentation, and anti‐frequency‐variation for single‐phase grid‐tied inverter

High‐order repetitive control can deal with period variation. An augmented second‐order repetitive control (RC) scheme is presented to improve system performance under grid frequency variation. Firstly, the relationship between proportional‐integral/inertial, multiple‐resonant, multi‐quasi‐resonant control, and second‐order RC is analysed. The weight range of second‐order RC is discussed. Then, a second‐order RC approach augmented by proportional control is proposed for a single‐phase grid‐tied inverter. Experiments are provided to verify the superiority of second‐order RC compared with single‐order RC under frequency variation.