Study of Control Strategy for Grid-connected Inverters Based on Dropped PLL

Power factor of grid-connected inverter with grid voltage feed-forward control is affected by the current-loop parameters and filter inductor.A novel control strategy based on dropped phase-locked loop（PLL） was proposed.The phase separation between the grid current and grid voltage was detected and the phase was used to calculate the PLL output frequency which determines the grid current phase.Unit power factor can be achieved and anti-islanding was also fulfilled.The control block diagram was given.The principle of the proposed method and the selection of droop coefficient were analyzed.The simulation and experiment results verify that the proposed method is effective in improving the power factor and the anti-islanding ability of grid-connected inverters.