Research On A New Harmonic Current Detection Method For Active Power Filter

With the rapid development of modern industrial technology,people pay more attention to the quality of life at the same time,the requirement of power quality is more and more strict.With the increase of a large number of nonlinear loads,a large number of harmonic components appear in the power grid.In serious cases,all kinds of protection and automatic control devices lose efficacy,affecting people's normal life.Active power filter(APF)has become one of the main methods of harmonic control in power system.It has good dynamic response performance and various compensation methods,and can compensate the harmonics of power network well.This paper first describes the background and research significance of harmonic control,and introduces the development status and trend of APF at home and abroad.Then,it classifies APF in detail,describes the specific working principle,and establishes the mathematical model of APF in the qd-rotating coordinate system.Secondly,in view of the unbalanced and distorted APF three-phase power network,which makes it impossible for the PLL in theqpii-harmonic current detection method to calculate accurate voltage frequency in real time,a new PLL based on synchronous coordinate system with adaptive notch filter and adaptive filter is proposed.The simulation results show that the proposed method can accurately and quickly extract the voltage frequency and avoid the influence on the accuracy of harmonic current detection.In addition,aiming at the contradiction between the convergence rate and the steady-state error of the traditional fixed step size,a new nonlinear model based on the Sigmoid variable step size function is designed.When the error is in the steady-state stage,the step size of the new function is smaller and the change is slower.Thirdly,in order to realize accurate and fast harmonic current tracking control,this paper adopts the voltage space vector pulse width modulation method,which includes sector judgment and selection,sector action time calculation and voltage switching vector calculation.The feasibility of the algorithm is verified by simulation.Finally,the hardware and software of APF control system are designed.Hardware design includes voltage and current signal acquisition and conditioning circuit,DSP core circuit,drive circuit and protection circuit.Software design includes APF system main program design,harmonic current detection program design,new SRF-PLL program design,space vector pulse width modulation program design.On this basis,a 100A/400 V activepower filter was developed in cooperation with the enterprise.APF load test and total harmonic compensation test were carried out,which proved the reliability of the experimental device.