| Traction converter is the main EMI source of electric locomotive,and its EMI intensity is the key factor for the vehicle to pass the EMC test.Among them,the cable is not only the main transmission path of the high-frequency interference signal in the converter,but also the efficient antenna of radiation emission and reception.Therefore,the in-depth study of the cable has a vital influence on solving the electromagnetic compatibility problem of the traction converter.In this paper,subway traction converter is taken as the research object,and the EMI of its power cables is systematically studied.Based on the research results of relevant literature,the following studies are made in this paper.Firstly,in order to establish the high-frequency circuit model of the cable,the parasitic parameter extraction of the cable is studied.The formula for calculating parasitic capacitance and inductance parameters of cable by mirror analysis method is derived.Numerical simulation software Q3 D is used to verify the correctness and application conditions of the mirror image analysis method.The influences of cable height above ground,cable spacing,cable insulating layer material and thickness on cable parasitic parameters are analyzed.Then,the parasitic parameters of external cable(parallel),internal cable(curved)and copper bar of converter box were extracted and analyzed by Q3 D software.A new method to extract the distribution parameters of curved cables in the box is put forward,and the correctness of the method is verified by comparing with the lumped parameters.Based on the multi-conductor transmission line model and the extracted distribution parameters,the high-frequency distributed parameter circuit model of cable and copper bar is established completely.This model can be applied to the research of various EMC problems such as conduction interference,radiated interference and crosstalk of converter.Based on the high frequency model of cable,a fast method for calculating the electric field intensity of cable far field radiation by using the multi-conductor transmission line equation and the electric dipole antenna model is proposed.The correctness and rapidity of the method are verified by comparing with the simulation results of CST cable radiation,and the high frequency circuit model of cable established in this paper is proved to be correct.In addition,the effects of the height and length of the cable on the intensity of the radiation electric field are analyzed by using the fast calculation method of the radiation emission,which provides guidance for the control of the radiation of the cable.Finally,the conduction interference mechanism of the converter is analyzed.Two main methods of conducting interference measurement on converter cables,current method and voltage method,are studied,and their applications,advantages and disadvantages are summarized.The method of measuring common mode interference and differential mode interference using oscilloscope instead of common mode separation device is put forward so as to avoid making complex separation device.The test method in this paper is of guiding significance for conducting interference test of various electrical equipment. |
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