| With the development of power electronic technology,various kinds of power electronic equipments have been widely used in the fields including industry,commerce and military.However,a large number of electronic equipments will produce serious electromagnetic interference and cause deterioration of electromagnetic environment.The electrical and electronic equipment will be endangered seriously,if no measures are taken.Therefore,there are more and more attention on the study of electromagnetic compatibility.In this thesis is researched the Flyback switching power supply,its conduction interference and inhibition are studied deeply.On the basis of summarizing massive domestic and foreign references,introduces the research results of electromagnetic interference of switching power supply,make the direction of research clear and lay the foundation for the behind research.The flyback switching power supply is took as an example to analyze the source of interference and the propagation path of electromagnetic interference in the power supply circuit.The thesis analyzes the coupling circuit of common-mode conduction noise and differential mode conduction noise in flyback switching power supply circuit mainly,and gives two methods for extracting the source impedance of electromagnetic interference noise.Then,the Insertion Loss Method and Two-Port ABCD Network Approach are studied.Baseed on the high-frequency model including power MOSFET's,rectifier diode's,inductance's,capacitance's,resistor's and high-frequency transformer's high-frequency model,a high frequency circuit model of flyback switching power supply is established.The high-frequency models of isolating transformer in flyback circuit are analyzed emphatically,including the three-capacitor model and the magneto-electric model.The three-capacitor model of the transformer reflects the electric field coupling characteristic in the transformer,it can effectively predict the coupling of common-mode conduction interference in transformers at low frequencies,but the accuracy is reduced in medium and high frequency band.Based on the three-capacitor model,the magneto-electric model considering the interaction between magnetic field and electric field,it can accurately reflect the magneto-electric effect inside transformer and the accuracy of prediction to common-mode conduction interference in transformers at high frequency.The filter is used to suppress the conduction interference of the switching power supply.The influence of different noise source impedance characteristics and different load impedance characteristics on the filter performance are analyzed emphatically.The suppression ability of three-terminal capacitance LC filter to conduction interference is also studied emphatically.The Tri-Terminal Capacitor LC filter can reduce the resonant point of the filter in the 150kHz?100MHz frequency band,and make the resonant frequency point of the filter push up to the high frequency point.Using PSpice simulation software,high-frequency simulation circuit model of flyback switching power supply with filter are built.The simulation of common-mode conduction interference and differential mode conduction interference is carried out.Frequency domain analysis,time domain analysis,and frequency domain analysis of noise voltage presented by decibel value are carried out to analyze the simulation results.These analyses are used to verify the effectiveness of high-frequency model predictive conduction interference and the effectiveness of filter on the suppression of conduction interference.For a flyback switching power supply which power is 85W,two-terminal capacitor and three-terminal capacitor LC EMI filter are constructed respectively.Test experiment of conduction interference of switching power supply are carried out to verified that the three-terminal capacitor LC filter has better conduction interference suppression effect than the two-terminal capacitor LC filter. |
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