An Improved Harmonic Detection Method for Active Power Filter

With the development of power systems, the harmonic problem has become more and more prominent. In the application of active power filters, the traditional ip-iq algorithm can only detect total harmonics and cannot obtain specific harmonics. To address this problem, this paper proposes an improved ip-iq algorithm for active power filters. This algorithm is improved based on the difference in separation objects of harmonic detection algorithms. It can convert specific harmonics into DC components. After low-pass filtering and inverse transformation, the specific harmonic components in the original three-phase current can be obtained. Compared with the traditional algorithm, mainly by modifying the transformation matrix <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$C_{x}$</tex> and its inverse matrix <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${C_{x}}^{-1}$</tex> according to the difference between positive and negative sequence harmonics, it is simple to implement in active power filters and does not require complex calculations, greatly expanding the harmonic detection range and accurately detecting specified harmonics. A simulation model is constructed using Matlab/Simulink software to detect the 5th and 7th harmonics under two conditions of different harmonic contents in grid current. The results show that in the application of active power filters, when the content of specified harmonics is large, the detection result is more accurate. When the content is small, although there may be errors due to interference from other harmonics, it is within an acceptable range. Thus, the feasibility and effectiveness of the improved ip-iq algorithm in detecting specific harmonics in active power filters are verified.