In order to ensure normal operation of grid-connected power converters under unbalanced

harmonic or distorted grid-voltage conditions

phase-locked loops（ PLL）

which are able to accurately and rapidly detect phase and frequency of positive-sequence components for power signals at the fundamental frequency are in great need.Conventional synchronous reference coordinate-PLL（ SRF-PLL） fails to satisfy the requirements due to its poor performance in harmonic suppression. Present a novel dual second-order generalized integrator-PLL（ DSOGI-PLL）algorithm. By introducing frequency-locked loop（ FLL）

DSOGI-PLL is frequency adaptive. Simulation and experimental results demonstrate that the algorithm can avoid effect of negative components of grid voltages and succeed in harmonics suppressing.