In order to meet the control requirements of the grid connected converter under the condition of asymmetry,DC component and harmonic. the positive sequence component,amplitude and fundamental frequency of the voltage signal should be detected accurately. The method based on dual second order generalized integrator FLL can extract synchronous signal under the voltage asymmetry and distortion. However,when the voltage signal contains DC component and multiple harmonics,the filtering effect of basic SOGI structure is not ideal,the waveform tracking is relatively large,and the tracking speed is reduced. In this paper,improved SOGI structure is proposed,which increase the differential node and the adaptive filter based on SOGI,and retain the advantages of SOGI-FLL. The amplitude and frequency of the voltage can be detected accurately and quickly,while it can well reduce frequency hopping fluctuation,harmonic filter and eliminate the DC component. MATLAB simulation results show that the improved method can accurately detect the positive sequence component and frequency of the fundamental wave under the condition of voltage signal asymmetry,DC component and multiple harmonics.