Research On Three-phase Four-leg APF Based On Improved Repetitive Control

Electrical energy substitution and clean alternatives,green development has become the theme of energy development in today's era.The demand of electricity is huge in our country.Its performance is not only in terms of electricity consumption,but also more strict requirements for power quality.In real life,non-linear and unbalanced loads are put into use in the power grid,causing severe harmonic pollution.The parallel type three-phase four-leg active power filter is an effective compensation device for solving the harmonic current pollution in the low-voltage distribution network.The harmonic current detection algorithm and the compensation current control strategy directly determine the harmonic compensation capability of APF.In the aspect of harmonic detection,an improved FBD harmonic detection algorithm is proposed in this paper.Accurate and rapid harmonic detection is the premise and foundation of active power filter excellent compensation performance.For traditional harmonic detection algorithms such as poor real-time performance and low detection accuracy,in this paper bases on traditional FBD detection algorithms and improves them.The symmetry component method is used to extract voltage phase information of the fundamental wave,an average algorithm is used instead of a low-pass filter,these measures have corrected the detection error of the phase-locked loop PLL when the voltage is distorted and solved the problem of the inherent delay of the low-pass filter LPF.The MATLAB simulation results show the effectiveness and feasibility of the improved FBD detection algorithm.In compensation current tracking control,in order to achieve better dynamic characteristics,in this paper,a compound control strategy combining double repeat control and PI control is proposed.For PI control,the detection error is large and the repeat control has problems of cycle delay and slow dynamic response.Firstly,it improves on the basis of repetitive control,introduces pre-adjustment parameters and combines with PI control to improve dynamic response characteristics,and then the improved repetitive control structure is inserted in the feedback control in parallel to form a dual-repetitive controller.Through the has compensated grid current THD value,the dynamic response speed when the load change and the tracking error analysis of compensating current and referenced command current,MATLAB simulation results show that the correctness and superiority of compound control strategy.Finally,the design of the parameters of the three-phase four-leg APF experimental prototype are given in this topic,including the selection of main circuit components and parameter setting,the hardware circuit design of each module and the late system software design.Through experiment,the improved repetitive control of the three-phase four-leg APF has been proved with good dynamic response and compensation.