Droop PLL for grid-connected inverter

Using grid voltage feed-forward control, the current-loop parameters and filter inductor affect the power factor of grid-connected inverter. Based on droop phase-locked loop (PLL) a novel control strategy is proposed. The phase difference between the grid current and grid voltage is detected and is used to calculate the output frequency of PLL. Unity power factor can be achieved without affecting quality of grid current. The control block diagram is given. The operating principle of the proposed PLL and the selection guidance of droop coefficient are analyzed. The simulation and experimental results verify that the proposed method is effective in improving the power factor.