The grid-connected inverter with an LCL-type filter has the ability of easily attenuating the high frequency current harmonics. But its internal filter is prone to cause self-resonance

and the inverter has limited ability to grid current harmonics induced by harmonically distorted voltage. In consideration of the self-resonance phenomenon

the resonance mechanism is analyzed on the basis of the traditional bridge-side current closed-loop

and the resonance damping based on the first-order differential feedforward of inductor current is adopted to damp resonance. Simultaneously the differential equation model of grid-connected inverter with an LCL-type filter is developed under harmonically distorted voltage. On the basis of damping resonance

direct current suppression strategy based grid-side harmonic current is mainly analyzed to achieve grid current compound resonance and harmonic suppression

which is chosen by a critical capacitance of the filter capacitor. The influence of the closed-loop parameters on system performance is analyzed and the design of control parameters is presented. The proposed strategy is finally verified by simulation and experimental results.This work is supported by National Natural Science Foundation of China (No. 51277051

No. 51277050).