Research On High Frequency Characteristics Of EMI Filter Based On Device Finite Element Modeling

EMI filter is a reliable and effective noise reduction equipment,but the actual performance of EMI filter differs greatly from the design expectation,mainly two reasons:One is that the impedance characteristics of the actual noise source are not consistent with the source impedance used in the design of the filter.The other is that in the high-frequency circuit,there are non-ideal characteristics of the device itself,high-frequency coupling between the devices and parasitic parameters of the circuit itself.Therefore,the analysis of the influence of source impedance on the performance of the filter,the accurate mastery of the source impedance characteristics and the establishment of a model that can accurately reflect the non-ideal characteristics of the components are of great importance for EMI filter insertion loss prediction and electromagnetic noise suppression research.Firstly,this dissertation analyzes the influence of source impedance characteristics on the performance of EMI filter's differential mode and common mode noise filtering.Through simulation analysis of the influence of source impedance on the performance of ?-type filter and T filter when the source impedance is resistive,inductive and capacitive,and on this basis,the basic structure selections of EMI filter is summarized.Secondly,the establishment of a capacitor,inductor,three-dimensional finite element model of common mode choke,through components non-ideal simulation and the measured impedance characteristics,the model is verified by can fully reflect the frequency characteristic of device,and device of the electromagnetic field distribution is studied based on this model and the coupling between the two common-mode inductor winding and the relative position relations,At the same time,the impedance characteristics of common mode inductor under three winding modes are simulated and analyzed.Finally,based on the finite element models of capacitor,inductor and common mode choke,a typical EMI filter structure finite element model is established.By comparing the simulation with the actual measurement of insertion loss,it is verified that the integrated modeling method can comprehensively consider the influence of high frequency characteristics of devices,high frequency coupling between devices and PCB layout parasitic parameters,and has a good high frequency characteristic prediction effect.Based on this modeling method,the influence of the layout of ? filter and T filter on the filter performance is studied,and the parasitic coupling parameters are extracted.A layout with better filtering performance is obtained by comparing the simulation results of the model,and the conclusion is verified by the actual measurement.