| With the rapid development of China's high-speed railway,the mix running of AC-DC locomotive and AC-DC-AC locomotive in China's electrified railway makes the harmonic frequency distribution of the traction power supply system wide,there are a lot of harmonics,and the quality of power is reduced.The extensive existence of harmonic currents will have a great impact on EMU power electronics and interfere with the communication system.Among them,the transmission characteristics of current transformers(CT)are affected,causes transmission error and the differential protection device malfunctions,in severe cases,it will directly endanger the safe and stable operation of the power system.Therefore,it is of great theoretical and practical significance to research the transmission error of CT in EMU under harmonic conditions.This article aims at the problem of transmission error of CT caused by harmonics in EMU,through the study of the characteristics of the harmonic current of the EMU,the simulation software is used to simulate the transmission characteristics of the CT in EMU under harmonic current conditions.The working mechanism and basic characteristics of CT such as operating characteristics,equivalent circuits,error calculation methods,and error influencing factors are studied;and study the traction main circuits of EMU and EMU,the distribution and effect of the CT of different types of EMU are analyzed;with harmonic conditions,the harmonic source is classified and the harm of harmonic to the traction power supply system of EMU is summarized,which lays a theoretical foundation for the research and analysis of the transmission characteristics of the CT under the following harmonic conditions.Through the analysis of the working principle of the EMU traction system,the harmonic source is mainly derived from the Four-quadrant Converter of the traction converter,which is influenced by its modulation method,switching frequency and other factors,the source of the high harmonic and low harmonic is analyzed theoretically;through the simulation analysis of the Four-quadrant Converter,the distribution characteristics of harmonic current of EMU are obtained,compared with the measured data,the harmonic current characteristics of the traction system of EMU is obtained,and the harmonic conditions of the simulation are established.Based on the limitation of the working characteristics of the EMU CT,through the analysis of the relevant current transformer models,the J-A model which is easier to simulate and more accurate is selected;according to the electromagnetic characteristics of the CT of the EMU,the simulation model of the CT is established by using the PSCAD/EMTDC electromagnetic transient analysis software,and the frequency response characteristics of theCT are simulated and analyzed,which can obtain the transmission characteristics of the CT loaded with different current frequencies.Finally,the simulation model of CT with harmonic current and basic wave current is established in the PSCAD/EMTDC electromagnetic transient analysis software,based on the analysis of the harmonic current characteristics of the EMU,the transmission characteristics of CT is simulated and analyzed with different harmonic frequencies,amplitude,initial phase and CT transfer characteristics under secondary load conditions,and the error curves caused by different simulation conditions are theoretically analyzed,so as to obtain the transmission characteristics of CT under harmonic conditions. |
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