Research On APF Harmonic Detection Algorithm Based On Second-order Generalized Integrator

With the development of economy,a large number of power electronic equipment and other nonlinear loads are widely used in all walks of life.In the process of power transmission and utilization,a variety of factors cause the distortion of voltage and current waveform,resulting in a large number of harmonics and more serious pollution to the power grid.Active Power Filter(APF)can effectively control harmonics,and its harmonic detection effects greatly affect the performance of APF.In this paper,aiming at the problem that the dc component,high harmonic and low harmonic of the power grid have a great influence on the accuracy of harmonic detection in the APF harmonic detection link,several common harmonic detection methods are analyzed,and an improved phase locked loop is proposed to improve the accuracy of harmonic detection,which can adapt to the complex voltage environment;Two improved harmonic detection algorithms based on Second-Order Generalized Integrator(SOGI)are presented.Ⅰtype algorithm on the structure of the traditional method of IP-IQ joined the modified SOGI filter and phase locked loop based on SOGI,improved Ⅱ type on the basis of improved Ⅰ type joined the specific harmonic filter module(harmonic cancellation module,HCM),first by HCM had a greater influence on the effective to filter the harmonic detection of low harmonic,then introduce the modified SOGI filter to eliminate the influence of the dc component and high harmonic,new type of phase-locked loop containing multiple harmonics in power grid voltage and dc component can provide stable under the condition of power grid voltage frequency,Therefore,the harmonic current can be detected more accurately.Specific research contents are as follows:(1)In the aspect of instantaneous reactive power theory,the theory and detection effect of p-q and ip-iq harmonic detection are compared and analyzed,and the detection accuracy of ip-iq algorithm in the case of dc component,high harmonic and low harmonic is simulated by means of simulation.The results show that: compared with the p-q method,the ip-iq harmonic detection performance is less affected by the network voltage imbalance,but the detection accuracy is poor when the network voltage contains dc component,high harmonic and low harmonic.(2)Aiming at the problem that the PLL has great influence on the detection accuracy of ip-iq method.The principle of phase-locked loop(PLL)in synchronous coordinate transformation is analyzed.When the grid voltage contains the negative sequence component of the fundamental wave,the two-power frequency fluctuation which has a great influence on the performance of the PLL is generated under the synchronous coordinate transformation system,thus affecting the performance of the harmonic detection algorithm.Therefore,by using the principle of the positive and negative sequence decoupling is proposed based on a modified second-order generalized integrator of phase-locked loop,based on the modified second-order generalized integrator of phase-locked loop effectively eliminate the influence of double frequency,the modified second-order generalized integrator based on traditional SOGI improved topology structure,effectively restrain the direct current component and high harmonic.(3)Aiming at the influence of low-order harmonics on harmonic detection accuracy.A special subharmonic elimination module for ip-iq method is proposed.In order to verify the specific Harmonic eliminating module and based on the generalized second-order phase-locked loop combination of integrator of IP-IQ algorithm feasibility and effectiveness,structures,the matlab simulation model,the simulation results show that the new IP-IQ Harmonic detection algorithm in the grid,including dc component and high Harmonic,under the condition of low Harmonic get Total aberration rate(Total Harmonic Distortion,THD)of tiny electric current,high precision,satisfy the relevant requirements.