Active power filter is a kind of device used for dynamic comprehensive compensation of the harmonics of power system

reactive power and negative sequence current

in which the detection circuit of harmonic current is an important point which decides the compensation performance. In this paper

the theoretical analysis for the modified detection method is performed on the basis of transient reactive power theory of three phase circuit. The simulation study is made through MATLAB

showing that filter with the method can real-time detect and eliminate harmonics. The correctness of the method is verified by both analysis and simulation results.