Research on digital implementation of proportional-resonant controller based on a three-phase PV grid-connected system

Based on a three-phase PV grid-connected inverter with LCL filter, a two-current-loop control strategy which utilizes the grid-current as the outer-loop variable and filter-capacitor current as the inner-loop is adopted. Since the decoupling of the LCL filter is too complicate under dq coordinates, a PR controller is adopted in the outer loop under alphaszlig coordinates to avoid the complicated decoupling process. The control strategy can get the same performance as PI controller under dq coordinate that they all can eliminate the static error. Another problem comes out that the limited numerical precision of fix-point DSP restricts the utilization of PR controller based on the traditional time shift operator q and its associated z-transform. In this paper, delta operator is adopted to overcome the disadvantages of time shift operator q to make the realization of PR controller using fix-point DSP possible. Experimental results are given to prove the correctness and feasibility the proposed method.