The Foundmental Research On The Design Of Circular Planar EMI Filter

With high frequency and integration being the current direction of power electronic devices,electromagnetic interference existing in the power circuit is becoming more and more serious.Designing EMI filter with high performance is now a hot topic. The traditional filter has no adequatehigh frequency performance, which is composed of discrete components and whose size is large.Therefore, the paper is to research the key technologies on the design of planar filter based onelectromagnetic integration.Firstly, for the analysis of the high-frequency characteristics of the integrated LC components,which is the basic unit of planar filter, we establish the model of high-frequency based on the broadtransmission line theory. Then, finite element analysis software is used to extract the electromagneticparameters of the unit length. The differentials in calculating the inductance parameter betweentraditional analytical and numerical method have been given. Finally, we measure the relativemagnetic permeability of the different magnetic material and provide guidance for future assessmentof the relative magnetic permeability frequency characteristic of the core surround the LC.Secondly, a new structure of copper windings coated with nickel is proposed to improve highfrequency performance. The AC resistance and current distribution are analysed between pure copperwinding and copper winding coated with nickel. Meanwhile, the share of energy between differentmaterials is extracted. It is confirmed that metal nickel is the proper material to improve the highfrequency perfoamance.Finally，because of the instability of the high permittivity substrate, it is necessary to measure thefrequency characteristics of the dielectric constant accurately. The paper presents two differentimpedance analyzer measurement programs. Combined with a silver-plated ceramic substrate, we canlearn the result distracted by homemade device has a certain reference value. By linear fitting curve ofthe dielectric constant, we obtain the linear coefficient of the relative dielectric constant andlogarithmic frequency. Finally, by solving different finite models of windings, it’s further confirmedthat the narrow and thick winding is conducive to reduce the parasitic capacitance.