Aiming at the synchronization problem of three-phase grid-connected converters in traffic microgrid under harmonic and unbalanced disturbance, an open-loop phase-locked method based on generalized delay signal superposition operator is proposed. The generalized delay signal superposition operator can quickly and correctly get the positive sequence and negative sequence fundamental information in bad power grid, and generate two groups of pure orthogonal signals; The open-loop phase synchronization algorithm designed on this basis does not need the closed-loop adjustment process, and reduces the complexity of the phase-locked algorithm while optimizing the dynamic response speed; The proposed open-loop phase-locked method exhibits superior synchronization performance compared to the classical method under various grid disturbances. This is validated through simulations and experiments. The research shows that: when the power grid has distortion, imbalance, amplitude jump, phase jump, frequency jump and other disturbances, the open-loop phase-locked method proposed can precisely capture the fundamental phase in a power frequency cycle, and has stronger robust performance than the traditional method. It is an effective method to realize the rapid synchronization of three-phase power signals under adverse grid conditions.