Improved Repetitive Control Strategy for Grid-Connected Inverter Under Weak Current Network

In a weak network, the power grid voltage feedforward will reduce the stability of the system, and the resonant feedforward strategy to improve the robust stability of grid-connected inverters will sacrifice the suppression ability of the power grid voltage distortion. The use of proportional and repetitive control can suppress the background harmonics of power grid voltage, but there is a problem of insufficient stability margin. On this basis, an improved repetitive control strategy is proposed to analyze the stability vector curve and amplitude-phase curve, and the phase margin of low frequency band is compensated by notch to improve the stability of the system, which can improve the robust stability of the system under the impedance change of the grid and suppress the subharmonic of the grid voltage. Finally, the experimental platform of 50 kW grid-connected inverter is built to verify the correctness of theoretical analysis and the effectiveness of the proposed improvement strategy.