Aiming at the problems of large phase error and weak anti-interference ability of the traditional ip-iq harmonic detection method under non-ideal grid conditions, this study proposes an improved scheme that integrates dual second-order generalised integral phase-locked loops (DSOGI-PLLs) and adaptive trapped low-pass filters (ANF-LPFs). The DSOGI-PLL is able to significantly improve the accuracy under voltage distortion and frequency fluctuation conditions through the orthogonal signal generator and frequency adaptive mechanism, and the ANF-LPF adopts a cascade structure to significantly reduce the harmonic distortion rate. The experimental results demonstrate that the proposed improved method significantly improves the detection accuracy and robustness under the complex grid environment, and shortens the dynamic adjustment time, and this study provides an efficient solution for grid-connected harmonic management of distributed power supply.