Power Factor Correction Technology Of Multi-pulse Rectifier At DC Side

With the development of power electronics,high power rectifier has been widely used in various field.However,the rectifying device has strongly nonlinear and time-varying characteristics that can bring serious harmonic pollution for the power grid.Multi-pulse rectifier technique is one of the main methods to solve harmonic pollution of the high power rectifier.In order to improve performance of the multi-pulse rectifier in harmonic suppression,this paper combines the multi-pulse rectifier technique with the harmonic suppression technique at DC side based on conventional 12-pulse rectifier and researches a 12-pulse rectifier with Boost converter,which could reduce input current harmonics effectively and increase power density.In order to increase power density of the multi-pulse rectifier,the optimal designed wye-connected autotransformer is researched which can reduce the bulk of the rectifier.The position parameter and the proportional parameter are defined to describe the winding configuration of the wye-connected autotransformer.By calculating the relationship between the position parameter and the proportional parameter,the voltages and currents of the windings are identified.The optimal winding configuration of the wye-connected autotransformer is obtained from the viewpoint of minimum equivalent kilovoltampere(k VA)rating by establishing the relationship between the equivalent k VA rating of wye-connected autotransformer and the position parameter.The experimental results indicate that the optimal autotransformer has the least equivalent k VA rating which is 21.18% and the simplest winding configuration which has only three windings in every core limb.In order to restrain the input current harmonics of 12-pulse rectifier at DC side,the harmonic suppression mechanism based on 12-pulse rectifier is studied.This paper analyzes the current characteristics of the designed rectifier on the AC side and DC side.By using swithching function,the relationship between the input currents and inductor currents of the rectifier is obtained and the modulation scheme of inductor current is devised.The kVA rating of wye-connected autotransformer is recalculated with the harmonic suppression at DC side and compared with conventional 12-pulse rectifier.Theoretical analysis shows that modulating the inductor currents as the specific sinusoidal envelope line can result in ideal sinusoidal input currents and the winding currents of wye-connected autotransformer are changed with the harmonic suppression at DC side leading to the increase in k VA rating of the wye-connected autotransformer.In order to verify the effect of harmonic suppression at DC side on input current of the 12-pulse rectifier,simulation and experiment are conducted in this paper.The control circuit and driving circuit are designed from the viewpoint of minimum input current harmonics.Detailed steps on the parameter design of the main circuit are also listed.Simulation is completed with the help of Matlab/Simulink,and a 1.2k W prototype is also presented.Simulation and experimental results show that the designed rectifer has excellent harmonic suppression performance with the THD(Total Harmonic Distortion)of input current of 4.6% and has the merits of high power density with the equivalent k VA rating of magnetic device of 28.21%.