Research On Control Strategy Of Active Power Filter Based On Repetitive Control

As the most widely used energy in today’s society,electric energy has the characteristics of cleanness,safety and easy conversion.Related power quality problems have attracted more and more attention.However,with more and more nonlinear loads invested in the power grid,problem of harmonic pollution in the power grid is becoming more and more serious.Therefore,harmonic control is of great significance.As an important solution of harmonic control,active power filter(APF)has the functions of harmonic compensation and power factor correction.This thesis mainly studies the harmonic current control strategy which directly affects the compensation performance of active power filter.First of all,this thesis introduces the classification of active power filter.According to the topology and working principle of three-phase three-wire parallel active power filter,a mathematical model is established,and several common harmonic current detection methods are compared.Based on analysis and research,the d-q method based on synchronous rotating coordinate transformation is selected as the harmonic detection algorithm of the active power filter.Secondly,in nonlinear systems,PI controller has poor ability to track high-frequency signals,but good dynamic response performance;Repetitive control based on internal model principle has natural advantages in high-frequency signal tracking,but the traditional repetitive control design has some problems such as poor dynamic response and low compensation accuracy.Therefore,this thesis proposes a compound control strategy to improve the fast repetitive control,which improves the internal model of repetitive control to reduce the inherent delay and improve the stability;Due to the characteristics of good adaptability of Fuzzy Adaptive PI control to system parameters and fast dynamic response,a double loop composite compensation current control strategy with improved fast repetitive control as the outer current loop and Fuzzy Adaptive PI control as the inner current loop is constructed,which combines the advantages of both to further improve the dynamic response speed and compensation accuracy of the system.The feasibility and superiority of the proposed control strategy are verified by building a simulation model in MATLAB.Thirdly,when the grid frequency of the fast repetitive controller is offset,the internal mode resonant frequency of the repetitive controller will deviate from the actual fundamental and other subharmonic frequencies,resulting in the reduction of the compensation control performance of the system.In order to solve the problem of frequency adaptation of fast repetitive controller,a composite control strategy based on improved frequency adaptive fast repetitive control is proposed in this thesis.Design of Thiran all-pass filter based on infinite impulse response is introduced into the internal model design of fast repetitive controller,which effectively solves the problem of frequency adaptation of fast repetitive control scheme and improves the stability of the system;Fuzzy adaptive PI control and frequency adaptive fast repetitive control are combined to form a double loop compound control,which takes into account the harmonic suppression performance and dynamic performance of the system.Correctness and effectiveness of the proposed control strategy are verified by MATLAB simulation.Finally,this thesis gives the system design of active power filter,mainly including the parameter design of main circuit components,hardware circuit design and system software architecture design,and the experimental verification is carried out on the APF experimental platform.Results show that the active power filter control strategy based on repetitive control method can effectively compensate the power grid harmonics,the harmonic control effect is excellent,and the steady-state and dynamic performance meet the design requirements.