A control strategy in a stationary frame for grid-connected inverter with LCL filter

By analyzing the mathematical model of the three-phase grid-connected inverter with LCL filter in the two-phase stationary coordinates, a quasi-PR controller which can track the grid current without steady error in stationary coordinates is proposed in this paper. To restrain the resonance caused by the insufficient damping, the capacitor current feedback is introduced to realize active damping. According to the requests of the stability, stability margin and steady-state error, the capacitor current feedback coefficient, resonant gain and proportional factor could be designed, respectively, by using frequency theory. The effectiveness of the adopted parameters design method and feasibility of the proposed control strategy are verified by simulation and experiment results.