Abstract: A single-phase harmonic detection method based on conservative power theory is proposed,which combines the second-order generalized integrator phase-locked loop to realize the extraction of fundamental voltage components and the suppression of harmonic voltage.The inspection method features simple principle, clear structure and easy operation. It is verified by simulation that the detection method is well applicable to both sinusoidal and non-sinusoidal grid voltage conditions with high detection accuracy and good dynamic performance while well compensating harmonic components and reactive power under sinusoidal and non-sinusoidal grid voltage conditions when it is applied in single-phase parallel-type active filters.