Research On The Key Technology Of Three-phase Four-arm Parallel APF

With the development of economy and technology,electrical power as a new clean energy has become an essential part of the industry and daily life.The power quality of low voltage distribution network is directly related to the safe of power systemoperation and normalpower usage of consumer.However,a large number ofharmonics are brought into low voltage distribution network which makes the power quality so poor because the widely use of nonlinear power electronic devicesand the access of more and more distribute generations.Therefore,it has an important significancetothe power grid and power consumersto study the methods of reducing harmonic and improve power quality of distribution network.The related concepts,causes,development processand harmful impacts to the gridof harmonics are introduced in this paper.Thenthe measures of harmonic governance and active power filterwere detailed analyzed,made a analysis of,parallel APF was selected as the main research object.And its working principleand main topology structure of circuit have been analyzed,and the basic theory of active power filter-instantaneous reactive power theory is also brought in upon the the traditional average power.Harmonic current detection is the base of the APF.This paper compares lots of existingharmonic current detection method,and on this basis,an improved p-qharmonic current detection methodbased on improper integralwas proposed.It canrealize the harmonic current detectionrapidly and efficiently under the condition of the distortedand asymmetricalvoltage which overcomes the drawback of traditional p-qdetection,and it also can detect harmonic current accuratelyby adjusting the gain coefficient without phase-locked loop.Control strategy of harmonic compensationis the key to produce the required compensation current,which plays a decisive role in the compensation result.Different control and trackingmethods are compared in this paper such as triangular wave comparison method and hysteresis current control method.An improved PR control strategywasproposedcombining with good select frequency character of the resonant controller,parameters debugging method of the controller is obtained after analyzing the influence of various controllerparameterson the control performance.Simulation results demonstrate that the improved PR controller can realize the reference current of instruction tracking without static errorstaticand satisfy the requirement of quickness.Three-dimensional spacevectorpulse width modulation(3D-SVPWM)in the a-b-c coordinates is adopt in this paper,which hasautilizationrateinDC voltageside and reduces the harmonic content,at the same time,eliminates the stepof coordinatetransformation of SVPWM involving under ?-?-0coordinates which making calculation more simple.The principle and processof 3D-SVPWMin a-b-c reference frame is detailed introducedin this paper.A complete APF model of three-phase four-arm was builtedbyusing the software of Matlab/Simulink.And then the result demonstrate that the proposed methodcan implement the compensation of system harmonic current accurately and rapidly under the condition of voltagethree-phasesymmetry and distortion.