A novel synchronizing signal detection scheme for the fundamental voltage during unbalanced and/or distorted grid voltage conditions is proposed. By adopting a new resonant-type phase locked loop（PLL） design， the phase tracking error caused by the grid faults can be quickly compensated， and the frequency variation and phase jitter can be effectively suppressed as well. This method can be used for detecting the frequency， amplitude and phase of the fundamental voltage under ideal grid condition， as well as the grid fault condition， which is related with the voltage dips， unbalance and harmonic distortion at both the steady state and transient state. Besides， the positive and negative components of the fundamental voltage， and the harmonic components can be separated completely and rapidly. Simulation and experimental results prove that the proposed algorithm is of high precision， fast dynamic response and strong practicability. It provides a reliable foundation for the control of grid connected power electronic devices， e.g.， wind turbine generators， grid-connected converters of solar photovoltaic， reversible variable speed drive system and dynamic reactive compensators and so on.