Study On Construction Method And Temperature Characteristics Of Broadband EMI Filter Model

The wide application of power electronics equipment has led to increasingly prominent electromagnetic compatibility problems.Electromagnetic interference not only affects the normal operation of the equipment,but also poses a potential threat to the safety of workers.At present,electromagnetic interference filters are usually used in power electronic equipment to deal with electromagnetic interference problems.For example,connecting EMI filters to the power line of the equipment can effectively suppress conducted EMI and make it meet the requirements of national electromagnetic compatibility standards.In some special applications,such as aerospace systems with high requirements for environmental adaptation,and GPRS base stations with harsh working environments,the performance of EMI filters needs to face the test of large temperature fluctuations.Based on this,this paper mainly studies the EMI filter model construction method and the influence of temperature on the attenuation performance of the EMI filter.Taking two kinds of parallel capacitor structure EMI filters as the research object,the equivalent circuit of each component inside the EMI filter is constructed,and the parasitic parameters of the main components of the EMI filter are measured by a precision impedance analyzer.Using the thermostat to change the environment temperature of EMI filter component,obtain the changing law of parasitic parameters under different temperature conditions,and then calculate the temperature coefficient of each parameter based on the extracted parasitic parameters,and establish the equivalent model of two kinds of structure EMI filter.The simulation results show that the transmission coefficient S₂₁ of the two filters with different structures in different temperature environments increases first and then decreases with the increase in temperature.In order to verify the above theory,two EMI filters corresponding to the simulation model were made,and built an experimental platform to measuring the transmission coefficient S₂₁.Using the thermostat to change the environment temperature of EMI filter,the S₂₁ parameters of the two EMI filters in different temperature environments are measured by a vector network analyzer,and the measurement results are in good agreement with the simulation results.It proves the accuracy of the equivalent model of the EMI filter which considers the influence of temperature and the feasibility of the modeling method.Through experiments and simulation results,it is found that with the increase of temperature,the overall trend of the attenuation performance of the parallel structure EMI filter and the anti-parallel structure EMI filter is increase first and then decrease,which is roughly the same as the trend of inductance value of common-mode choke.With different structures the inflection point of the filter is different,which shows that the temperature mainly affects the transmission coefficient S₂₁ of the filter by affecting the inductance value of the common-mode choke.