A novel current dual-loop control strategy for three-phase grid-connected VSI with LCL filter

In grid-connected PV inverter system, grid voltage distortion gives rise to extra grid current harmonics. This paper first analyzes the shortage of inverter output current control scheme in suppressing the grid current harmonics caused by grid voltage distortion for grid-connected three-phase voltage source inverter (VSI) with LCL filter under d-q rotating frame. To damp these harmonics, we propose a novel dual-loop control scheme in which inverter output current inner loop is controlled by PI controller and grid current outer loop is regulated by the combination of PI and PR controller. PR controller yields a good performance in damping special order harmonics under this control scheme. Output admittance of the system is derived to analyze the impact of grid voltage distortion on grid current. Stability and effectiveness of this proposed strategy are verified with theoretical analysis as well as simulation and experimental results under 100kW PV inverter prototype.