State feedback control for single-phase grid-connected inverter under weak grid

Investigated in this paper is the use of state variable feedback control combined with a PI controller for a single-phase grid-connected inverter with an LC filter operating under weak grid conditions. This condition is characterized by a grid impedance much larger than the inductance in the LC filter. Under weak grid conditions, variations in the grid impedance can degrade the performance of the inverter. State feedback control offers full controllability, which can enhance stability and increase damping to reduce the LC filter resonance. Therefore, state feedback control combined with a PI controller has been utilized to maintain inverter performance under weak grid conditions. The impact of grid impedance variations on the closed-loop system has been analyzed. Circuit parameter sensitivity analysis is also performed to verify the robustness of this method to parameter uncertainty. Compared with conventional current feedback control (PI control, PR control), the proposed method is more robust to the grid impedance variation even under a distorted grid. Analysis and experimental results demonstrate the effectiveness of the proposed control method. Also, the harmonic rejection ability is analyzed.