Study on control strategy and application of a new harmonic detectionmethod in three-phase four-wire APF

摘要

In the three-phase four-wire low-voltage distribution network, a large number of nonlinear loadsare put into use, whichmakes the harmonic and three-phase imbalance problems of a three-phasefour-wire system more and more prominent. In addition, it seriously affects the energy qualityof the power network. The three-phase four-wire active power filter (APF) is one of the effectivemeasures to solve these problems. In this paper, a new harmonic detection method for thethree-phase four-wire APF is proposed, and it is applied to the control strategy of three-phasefour-wire APF. Then, the advantages and disadvantages of various detection algorithms of harmoniccurrent in a three-phase four-wire system are summarized. The digital phase-lockedtechnology based on a generalized integrator is studied, and the method of extracting thepositive-sequence component of fundamental wave voltage by using the frequency-selectingcharacteristic of a generalized integrator is put forward. The generalized integrator and theip-iq method are combined to realize the detection of any order harmonics. A novel method ofextracting fundamental wave components from three-phase four-wire APF harmonics using theensemble empirical mode decomposition (EEMD) algorithm is put forward, and the function ofupper and lower envelopes is optimized by using a cubic spline fitting curve in the process ofEEMD. In order to reduce the operation time of the EEMD algorithm and improve the efficiencyand real-time function of harmonic detection, the cubic spline fitting curve is used to obtain thefunction of upper and lower envelopes in the process of decomposition.