In order to detect the amplitude, phase and frequency of the grid voltage quickly and accurately, this paper analyzes the method of symmetrical components and principle of single synchronous reference frame phase locked loop. A design method of the generalized integrator phase locked loop is presented, of which the positive and negative components are distinguished in αβ coordinate system, and the phase and frequency of positive sequence voltage are locked. And it takes use of Matlab/Simulink to carry on the research of single synchronous reference frame phase-locked loop and generalized integrator phase locked loop. Simulation results show that the generalized integrator phase locked loop can get amplitude, phase and frequency of the grid voltage accurately when the grid is unbalanced, and the frequency has good adaptiveness and has a certain inhibiting effect on low-order harmonic.