Research On Online Measurement Method Of Noise Source Impedance Based On Emi Filter Design

Electromagnetic compatibility is an important condition for safe and reliable operation of electrical equipment.With the power devices used in power electronic system more and more widely,and towards the trend of high frequency and miniaturization,electromagnetic interference problem is becoming more and more serious.There are many methods to suppress the conducted electromagnetic interference of electrical and electronic equipment,among which the filtering technology is one of the most widely used and effective methods,and it is also the main auxiliary measure to ensure the reliable operation of partial or overall equipment.In order to evaluate the performance of EMI filter,50Ω signal source is generally used as interference source,and 50Ω spectrum analyzer is used as load to test the performance of EMI filter.However,there are great differences between the actual working condition and the experimental condition,so it is difficult to realize the 50 Ω-50 Ω system,which makes the actual performance of the filter inconsistent with the experimental conditions.Because the designed filter impedance cannot be changed,but when the noise source impedance changes,the performance of the filter may not achieve the desired effect.Therefore,the impedance relationship is very important for the design of the filter,and the measurement and analysis of the noise source impedance is the prerequisite for the design of the filter.In order to measure the noise source impedance more accurately,analyzes the advantages and disadvantages of different noise source impedance measurement methods,and proposes a new impedance measurement method based on the traditional measurement methods.Firstly,based on the theory of two port network,the principle of the measurement method is analyzed,and the calibration method of current probe is improved.Secondly,the port structure of the measurement method is analyzed,and the noise source impedance is calculated by using the theory of microwave transmission.Finally,the correctness and feasibility of the proposed method are verified by experiments.Finally,the correctness and feasibility of the proposed method are verified by experiments.This method solves the problems of narrow measurement band and complex calibration process of probe in traditional impedance measurement method,which will help to improve the design theory of EMI filter,improve the working performance of EMI filter,further improve the safety and reliability of electrical and electronic equipment,and promote the development of electrical and electronic equipment towards high frequency and miniaturization.The temperature fluctuation of EMI filter caused by power loss,ambient temperature and surrounding equipment temperature will affect the impedance frequency characteristics of common mode choke,capacitance and resistance,and then change the characteristics of the whole filter circuit.Based on this,based on the modeling of capacitor and common mode choke,the resistance frequency characteristics of capacitor and common mode choke under different working conditions are measured,the extraction method of model parameters is studied,and the sensitivity of each parameter to temperature change is analyzed.