Phase-Locked Loop (PLL) with a pre-filtering stage is a powerful tool to study the grid synchronization technology.However,the dynamic performance of this class of commonly used PLL (e.g.,second-order generalized integrator PLL,complex-coefficient filter PLL) is constrained by the low cut-off frequency of the front-stage structure.Thus,a three-phase PLL technique based on fractional-order generalized integrator is proposed.The front-stage filter of the PLL is composed of fractional-order integrators,which can generate two diagonal signals whose phase difference is 45°.Through the correlation linear operation,the positive- and negative-sequence components of the grid voltage can be extracted from the diagonal signals.Combined with the post-stage synchronous rotating frame PLL,a mathematical model of the entire PLL system is built,and the third order optimal design method is used to correct the system and determine the related control parameters.The study shows that,the cut-off frequency of the fractional-order generalized integrator is obviously higher than that of the second-order generalized integrator,which is helpful to improve the dynamic quality of the PLL system.The simulation and experimental results show that the dynamic performance of the proposed PLL is better than that of the multiple second-order generalized integrator PLL.