Improved Dual-Mode Repetitive Control for Grid-Connected Inverters

In this paper, a dual-mode repetitive control in parallel with proportional gain is proposed, and a fractional delay is added in the case of grid frequency perturbation to ensure the suppression capability of output current harmonics. Firstly, the principle of the compound controller is analysed. Secondly, the theoretical basis for the stability and parameter design of the composite controller is analysed, and the parameter design is carried out based on a single-phase LCL-type grid-connected inverter. Finally, the fractional-delay part is added under consideration of grid frequency disturbance and its stability is verified. The experimental results verify that the composite controller proposed in this paper has excellent harmonic suppression capability and fast dynamic performance.