According to the operating characteristic of the three-level NPC converter, the grid-connected control model based on the dual second order generalized integrator phase locked loop(DSOGI-PLL) is designed. The second order generalized integrator(SOGI) is used to detect the positive-sequence component and the negative-sequence component of the grid voltage under unbalanced conditions. Combining with the characteristics of the frequency-adaptive SOGI and the characteristics of the synchronous reference frame phased lock loop(SRF-PLL), the design of the phase locked loop under unbalanced conditions is designed . From the results of the simulation, it can be concluded that the DSOGI-PLL is frequency-adaptive and can track the frequency and the phase of the grid voltage accurately and quickly. Finally, the practicability of the DSOGI-PLL is verified on a DSP and FPGA controlled SVG equipment .