Study On Three-phase Four-leg Shunt APF With One-cyle Control

Three-phase four-wire power supply system has been widely used in the low-voltage grid in recent years,but with the increase of three phase unbalanced nonlinearloads,harm of harmonic, reactive and neutral current is growing,affecting the powerquality seriously.Aimed at this issue,on the basis of the topology of active powerfilter (APF),combined with the one-cycle control strategy, research and design three-phase four-leg shunt APF with one-cycle control.Firstly, this thesis introduces the general research profile of conventional APFand make detailed analysis of one-cycle control theory and its application in APF.Atthe same time,by comparing the structure of three single-phase bridge,three-leg andfor-leg in three-phase four-wire APF,choose four-leg as the main circuit topologystructure finally.Secondly,in view of the equivalent circuit of system in switch period,deriving the control equations,base on which to establish system model and thendetermine the controller structure and analyzes its realization process.On thisbasis,from the aspects of current tracking performance,the stability of the system aswell as the switch stress,the important parameters of main circuit and control circuitis designed.Again,aimed at the unbalanced three-phase rectifier bridge load,carry outsimulation studies by using MATLAB/simulink.Make spectrum analysis of currentwaveform that before and after the compensation by using FFT analysis tool,andcompare odd harmonic content in list.Finally,design the system and build theexperiment platform,choose PIC18F2331to provide clock for one-cycle controllerand realize the closed loop control of dc voltage.Simulation and experimental results show that three-phase four leg shunt APFwith one-cycle control designed in this paper,can compensate harmonic,reactive andneutral current, has a good performance.