Research On Radiation EMI Characteristics Of Traction Converter System Of High Speed EMU

Our country’s high-speed EMUs have developed rapidly from introduction to innovation.The operating speed and power level of EMUs have been improved.The electromagnetic environment in the EMUs has become extremely complicated.It is difficult to guarantee electromagnetic compatibility.The vehicle radiation emission test is an electromagnetic compatibility standard test formulated by the railway,which stipulates the electromagnetic field limit requirements in different frequency bands.But so far,there are still some EMUs that exceed the standard limit in the vehicle radiation emission test and need to be tested and rectified.The traction converter system is the main factor of vehicle radiation emission.The internal voltage level of the system is high,the switching frequency is fast,the frequency spectrum is rich,and the energy is large.The external cable straddles the vehicle as long as tens of meters.The "antenna effect" will significantly affect the high speed.The electromagnetic environment outside the EMUs.Therefore,it is necessary to take electromagnetic radiation emission into consideration in the initial design stage.Carry out research on the radiated EMI prediction of the traction converter system of high-speed EMUs.Clarify the electromagnetic radiation emission characteristics of the traction converter system of high-speed EMUs.Ensure that the high-speed EMU has a friendly electromagnetic environment.In this paper,according to the internal working principle of a certain type of high-speed EMU traction converter,it is determined that the main interference source is the rapid sudden change of the voltage and current at the midpoint of the bridge arm when the switching device is working.Combining the circuit topology of the traction converter system and the grounding system,it is concluded that the connecting cables in the system play the main role of radiation.Secondly,the radiation mechanism of unshielded cables and shielded cables is analyzed by the electric dipole approximation method.The general solution process of cable radiation is given.The influence of cable wiring parameters,braided layer structure parameters and shielding layer grounding method on the regularity of cable radiation is discussed.Subsequently,a method of using the transfer function simulation curve combined with the test data to inversely obtain the common mode interference source of the shielded cable is proposed.And carried out experimental tests based on the scattering parameters to verify the accuracy of the simulation method and model.Finally,the process of electromagnetic radiation prediction by the transfer function method is introduced.Modular modeling of key cables,traction motors,and traction transformers was performed.The prediction model of radiated EMI of the whole vehicle of high-speed EMU is obtained.The field-line joint simulation is carried out to find out the general law of electromagnetic radiation of the traction converter system,and at the same time,the 10 meter method test is carried out according to the relevant standards.The research results of this paper are as follows.The cable length is less than half the wavelength corresponding to the interference frequency.Reducing the cable length can suppress the cable radiation emission.Reducing the height of the cable from the ground,increasing the braided coverage of the braided shielding layer,and double-ended grounding of the cable shielding layer have the effect of reducing radiation emission.The conduction emission of the shielded cable tested by the current probe method cannot be directly used as the interference source of the system radiation emission.The proposed transfer function method reversely deduces the test results to obtain the inner conductor current,which lays the foundation for the radiation emission analysis of shielded cables.The general law of electromagnetic radiation of the traction converter system is obtained by the prediction model of the whole vehicle radiation of the high-speed EMU.And through the vehicle radiation emission test to obtain the high-speed EMU vehicle magnetic field radiation emission characteristics.The comparison of simulation results and test results verifies that the radiated EMI model of the traction converter system of high-speed EMUs established in this paper can be used for the prediction of vehicle radiation electromagnetic compatibility,which provides a basis for system-level electromagnetic compatibility design and rectification of high-speed EMUs.