A single-phase grid synchronization method based on frequency locked loop for PV grid-connected inverter under weak grid

One of the main electrical characteristics of weak grid is high grid impedance, which will easily lead to harmonic resonance and grid voltage waveform distortion. Distorted grid voltage can make the phase-locked loop of photovoltaic (PV) grid-connected inverter occur deviation even failure and power quality deteriorates. Aiming at the problem, this paper takes the LC-type PV power generation system as study object, studies the effects on system of different grid conditions, adopts a second-order generalized integrator frequency-locked loop(SOGI-FLL) grid synchronization method under weak grid to realize grid-connection securely and improve the grid current quality. Finally the simulation and experimental results are given to demonstrate the validity of the proposed method applying to the single-phase PV power generation system under weak grid.