The Control Strategy And Application Optimization Research Of Three Phase Four Wire System Active Power Filter

In low voltage distribution network,there are two main power quality problems: one is the large three-phase harmonic currents;the second is the big zero line currents.Active power filter is the power electronic device of relatively advanced compensation harmonic,and good real-time and high compensation precision of active power filter is gradually replacing the passive power filter.In the past,main research object of many scholars are three-phase three-wire SAPF and hybrid SAPF combined with PPF in high voltage system.But,three-phase four-wire SAPF in low voltage system is less studied.In this paper,three-phase four-wire system SAFP is the research object,the main research content is as follows:1、Three-phase-four-wire SAPF is used to solve large harmful power quality problems of low voltage distribution network.Two kinds of classic SAPF main circuit structure of Three-phase four-wire SAPF are analyzed.Zero line current compensation ability of two kinds of SAPF structure,control strategy design and economy are also analyzed and three-phase four-wire SAPF of four bridge arm main circuit is chosen as the main research object.2、Mathematical model of the low frequency condition is established according to SAPF structure and then first-order Linear active disturbance rejection controller and bang-bang controller are designed relatively as three phase current loop controller and zero current loop.Because of LADRC characteristics of not depending on the accurate mathematical model of research object and strong anti-interference,APF has a good compensation precision and anti-interference characteristic.First-order LADRC is a feedback system,and its nature is the stability of the system,and the key problem of control system is anti-interference characteristic.Taking advantage of classical control theory to analyze convergence and errors of second-order linear extended state observer in frequency domain;anti-interference characteristics and stability problems are deduced based on three-phase four-wire system APF system of first-order LADRC.3、In the application process of active power filter,the optimal installation location selection will help to improve the compensation effect of SAPF.On the base of harmonic domain model of distribution networks and the appropriate harmonic objective function and a guideline of optimization idea,SAPF optimal installation point is determined using nodal admittance matrix in power distribution network based on the analysis of frequency domain.On the basis of this method,a 3 node 7 branch simple distribution network as an example is proposed to simulate and detailed simulation results are given.This method has certain significance for optimal installation position of SAPF in low voltage distribution network.