There are many grid faults in large-scale renewable energy generations. Such as Voltage drop, Frequency variations and harmonic distortion, Which demands the grid-connected power inverters could properly synchronized with the grid, Supporting the grid service (voltage/ frequency)even if the grid is polluted .so the better PLL or FLL is expected to achieve it. In this paper, a frequency locked loop technology based on the cascaded second-order generalized integrators (SOGI) is analyzed, which could accurately and rapidly extract the positive and negative sequence from the polluted grid voltage and make frequency adaptive. Results show its effectiveness and feasibility.