Research On Three Phase Active Power Filter Harmonic Detection Method And Phase-locked Loop Technology

With the increase of harmonics in the power grid,the active power filter(APF)is particularly important in the field of harmonic suppression.The harmonic detection link and grid connection technology also are particularly important in APF.The traditional i_p-i_q method requires the grid synchronization technology to track the grid voltage,so that the angle of the monitored grid voltage is used for the Park transformation;on the other hand,the current obtained by the Park transformation is filtered by a low-pass filter.The fundamental current is obtained,and the load current and the fundamental current are differentiated to extract the harmonic current.The i_p-i_q method also has its inherent shortcomings:the structure is more complex,and the use of the digital low-pass filter(LPF)greatly extends the harmonic detection time.On this basis,this paper uses the SAI structure to extract the characteristics of arbitrary positive and negative sequence waves.On the basis of omitting the Park transform and digital low-pass filter,the positive sequence fundamental wave extraction of SAI is used to form a link.A new full current harmonic detection method is proposed based on SAI.Compared with the original i_p-i_q method,the harmonic detection method has a simpler structure,shortens the harmonic detection time,and slightly improves the accuracy.Based on the idea proposed by the SAI harmonic detection method,this paper also uses double self-tuning second order generalized integrator(DSSOGI)structure to replace the digital low-pass filter in the i_p-i_q method and also omits the Park transform link.The new proposed harmonic detection method also be simpler in structure than the i_p-i_q method and its rapidity increases.In the synchronous technology tracking of the grid voltage,the article is based on obtaining a more accurate grid voltage signal,the SAI structure can extract the performance of the arbitrary frequency voltage of the grid voltage,this structure and SRF-PLL combination to proposed a new phase-locked loop method that can track the grid voltage.The simulation and experiment prove that the method based on SAI structure of phase-locked loop technology can be applied to three-phase power grid unbalance(voltage dropped or swelled),harmonic pollution,frequency hopping and DC voltage offset of the non-ideal power grid conditions.The ROR structure and SRF-PLL combination to proposed a new phase-locked loop method that can track the grid voltage.The simulation and experiment prove that the method based on ROR structure of phase-locked loop technology can be applied to three-phase power grid unbalance(voltage dropped or swelled),harmonic pollution and DC voltage offset of the non-ideal power grid conditions.Finally,based on the matlab simulation,the theory described in this paper is based on the experimental verification of the three-phase shunt active power filter prototype based on DSP control.Finally,the experiment verifies the feasibility and effectiveness of the subject.