The paper presents a PLL based on double second-order generalized integral (DSOGI-PLL) of abstracting grid voltage phase quickly and accurately for low accuracy and slow dynamic response of traditional PLL in the case of the unbalanced grid voltage in grid-connected PV systems. It can effectively extract the grid voltage positive sequence component, by using generalized integral and standard three-phase locked loop. Finally, the paper builds simulation for two-phase grid voltage drop and three-phase grid voltage unbalanced drop, and then uses DSP to verify it. Simulation results show that the PLL can provide more precise control reference for the grid-connected inverter, by which the stability and effectiveness of grid power generation systems are improved.