An averaged switching model of grid-connected inverter using dual-loop current control with LCL-filter in discrete domain is built under stationary frame. A proportional resonant (PR) regulator is adopted in the current-loop to track the given fundamental sinusoidal current without steady state error. In addition, in order to reduce the low frequency harmonics, the resonance of 5th harmonics is adopted. Because the system is of high order and complex, the theory of root locus is proposed to analyze the influence of parameters in PR regulator, the influence of digital delay, and the LCL-filter. Based on the theoretical analysis, the poles can be properly selected to guarantee the stability of the system and the performance of current-loop during wide grid-fed power. Finally, a 10 kW prototype of grid-connected inverter with LCL-filter is set up to verify the effectiveness, practicality, and robustness of the proposed design method.
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