In order to continuously control the power of the power grid under grid faults, avoid the protection dropout of the converter, and improve the transient fault ride-through capability. This paper proposes a novel frequency-adaptive grid-side converter grid synchronization technology, namely the dual second-order generalized integrator-frequency-locked loop (DSOGI-FLL). This new detector consists of three basic functional modules: orthogonal signal generator, positive and negative sequence component calculator, and frequency-locked loop. This paper conducts a detailed study of DSOGI-FLL, builds a model based on the MATLAB simulation platform for simulation analysis. The results show that DSOGI-FLL can improve the dynamic response performance of the system under unbalanced grid voltage conditions, and achieve fast, accurate detection and stable tracking of the grid voltage.