Research On Prediction And Suppression Of Conducted Interference Of Flyback Auxiliary Power Supply For A Vehicle Inverter

Flyback power supply is often used as auxiliary power supply in inverter,which has a great influence on CISPR25 EMC test result of vehicle inverter.Therefore,the research on prediction and suppression of EMI performance to vehicle inverter has great practical application value.In this thesis,the research object is flyback auxiliary power supply of vehicle inverter.Taking the prediction and suppression of conducted electromagnetic interference of flyback power supply as the main research object.The simulation model of conducted interference is built in Saber,and the EMI filter to restrain the conductive EMI noise is designed.For flyback auxiliary power supply,the modeling process of conduction interference is analyzed in detail.The conducted interference paths are divided into differential mode and common mode.Determine the main interference source and coupling path in flyback auxiliary power supply,which contribute to the effective prediction modeling and suppression design method of conducted interference discussed later.The high frequency transformer in this project needs to build a precise wide band model from 150 k Hz to 108 MHz.Based on the analysis of high frequency models of single winding transformer and multi-winding transformer,an effective model of high frequency transformer at 10 MHz is established by measuring and parameter fitting.Then the model at 108 MHz is established by expanding 10 MHz EMI model to higher frequency with Foster circuit model.Comparing with the measured and simulated result,the accuracy of the model to high frequency transformer at 108 MHz is verified.High frequency models of active and passive components are established with extracting the parasitic parameters among PCB in this thesis.The conducted interference model of flyback power supply is established and simulated by Saber.Through the comparison of simulation and measurement results to the voltage across drain-source of MOS transistor and the voltage across LISN,the effectiveness is verified further.It is proved that the model achieves effective prediction in a certain frequency band with desired accuracy.The filtering technology is easy to realize with good restraining effect.Therefore,the filtering method is chosen to restrain the conducted EMI noise of flyback auxiliary power supply,and good effect is achieved by the LCL EMI filter.In this thesis,Saber is used to predict the conducted interference of flybackpower supply.The procedure of this study has reference value for conducting interference modeling of other switching power supply.In this paper,LCL filter is used as EMI suppression measure,which can also be used as reference for EMI suppression technology to switching power supply with other topology.