Modeling Of High-frequency Characteristics Of Magnetic Bead Components And Its Application In Radiated EMI

With the miniaturization of circuit PCB board getting higher and higher,the electromagnetic interference problem faced by electronic products is becoming more and more serious.There are many kinds of radiation sources in electronic products and the generation mechanism of radiation noise is complex.As a convenient component to install,it is of great significance to study the characteristics and applications of ferrite beads to suppress radiation electromagnetic interference.In this thesis,the impedance characteristics of magnetic beads at high frequencies are taken as the research object,the equivalent circuit model of magnetic beads is established,the equivalent parameters of the model are extracted,the non-ideal characteristics of magnetic beads at high frequencies are explored,and a compensation method is proposed according to the mechanism of magnetic beads for inhibiting radiated EMI.Finally,the improvement of magnetic beads inhibition effect after compensation is verified by experiments.The specific contents are as follows:Firstly,based on the mechanism research of magnetic beads inhibiting radiated EMI,a circuit model of high frequency characteristics of magnetic beads is established and equivalent parameters of the model are extracted.Combining the principle of magnetic beads to suppress radiated electromagnetic interference and the definition of impedance,the high frequency characteristic model of magnetic beads impedance is established,and the calculation formula of magnetic beads impedance is deduced.Levinberg-marquardt method in the least square method is analyzed in detail and applied to parameter extraction of magnetic bead impedance.Then,because the iteration step size and initial value of Levinberg-marquardt are not easy to choose,the genetic algorithm is used to extract the equivalent parameters of the model.The fitting results of the two algorithms are close to the actual impedance of magnetic beads,which verifies the correctness of the model.Last but not least,the accuracy and speed of the fitting results of the above two algorithms are compared.Secondly,propose a compensation method for high-frequency non-ideal characteristics of magnetic beads and carry out simulation analysis to explore the magnetic bead impedance extraction experiment.Based on the high frequency equivalent circuit of magnetic beads,the non-ideal characteristics of magnetic beads are analyzed,and the compensation method is designed,and the impedance calculation formula after magnetic beads compensation is deduced.In order to compare the effects of different compensation methods,PSIM and MATLAB software are used to simulate the compensation methods,and the EMI spectrum of the circuit after magnetic bead compensation is obtained.Through comparison,an effective compensation method is obtained.Hardware and software experimental platform is built,and the vector network analyzer is used to extract the impedance of magnetic beads before and after compensation.Finally,the magnetic bead compensation method proposed in this thesis is applied to suppress EMI radiated by switching power supply.The principle of switching power supply and the mechanism of EMI emission are analyzed.PSIM and MATLAB software and 3m method semi anechoic chamber are used to simulate and experimentally analyze the EMI emission generated by switching power supply before and after magnetic bead compensation respectively.The effectiveness and practicability of the compensation method used in the experiment are verified,which provides theoretical reference and practical basis for the application of magnetic beads in EMI emission.