In view of the shortcomings of the traditional i

p

-i

q

harmonic detection algorithms based on the instantaneous reactive power theory

a kind of orientation method of virtual flux linkage observation based on composite third order generalized integrator is proposed and is used in i

p

-i

q

harmonic detection algorithm.The method uses the virtual grid flux linkage as an improved link of the phase-locked loop

uses the composite third-order generalized integrator and the positive and negative sequence component calculation module to realize the extraction of the positive-order flux linkage;on the basis of accurately locking the phase angle and frequency of the grid

e

liminates the detection error due to asymmetrical grid voltage

wave distortion and injection of DC offset component which is caused by the traditional i

p

-i

q

harmonic detection algorithm.It is shown by the simulation and experiment that the method after modification is basically free from severe condition of grid side

the fundamental current obtained by harmonic detection has basically no distortion

can achieve real time tracking frequency variation

and the effectiveness of virtual flux linkage orientation method based on composite third order generalized integrator proposed in this paper is proved.