Design of a composite repetitive controller for grid-connected inverters with a notch filter

To address the resonance peak issue of LCL (Inductor capacitor inductor) grid-connected inverters at the resonant frequency and reduce system losses caused by passive damping, this paper proposes a novel plug-in composite repetitive controller based on an active damping strategy utilizing a notch filter, along with detailed parameter design for the controller. Simulation results demonstrate that the notch filter-based repetitive controller maintains high gain at the fundamental frequency while exhibiting rapid gain attenuation at higher frequencies. Since the harmonic content of the inverter system is predominantly concentrated in the low-frequency range, the controller achieves excellent harmonic suppression performance within the low-frequency region. The low gain at high frequencies enhances system stability. Compared with conventional repetitive controllers, the proposed controller adopts a low-loss notch filter damping method, preserves the superior harmonic suppression capability (the grid current harmonic is reduced by 1.37 %), and improves system stability.