Research On Thermo-electric Model And Reduction Of The Junction Temperature Of EV Converters

With the development of electric vehicle(EV), the higher reliability for EV converter has been required. EV converter operates in high temperature environment(close to engine) and load variability. Therefore, power device’s junction temperature and junction temperature fluctuations are most important factors that influence the reliability of EV converter systems. In order to improve the reliability of power electronic devices, the research on junction temperature and the junction temperature fluctuations of the power device is essential. In this thesis, the thermoelectric model of EV inverter is presented. And the junction temperature and the junction temperature fluctuation of power device in EV inverter have been studied under different conditions. In addition, the ways of junction temperature improvement have been studied.Firstly, the dynamic characteristic of power device have been analyzed, and with SPWM strategy as examples, power losses have been calculated. Meanwhile, the junction temperature of power device has been calculated.Secondly, thermoelectric model of three-phase inverter is set up in the Matlab/Simulink. And the simulation results of Matlab/Simulink are consistent with the simulation results of IPOSIM software. Besides, the thermoelectric model of EV inverter is presented based on the thermo-electric model of three-phase inverter. And the junction temperature and the junction temperature fluctuation of power device in EV inverter have been studied under different conditions(rating, lowing speed, acceleration). The research shows larger junction temperature fluctuations of power device in EV inverter have been appeared under lowing speed and maximum junction temperature of power device have been appeared under starting conditions.Thirdly, a junction temperature measurement platform have been built. The output operations of EV converter under different conditions are simulated by active load. The results show that larger junction temperature fluctuations of power device have been appeared under low output frequency. To improve the junction temperature of power device under low output frequency, the junction temperature has been studied under different switching frequencies and different output current.Lastly, a comparison between the dynamic characteristic, anti-parallel diode reverse recovery and switching losses of SiC MOSFET and Si IGBT are studied via double pulse(DP) test. Compared to conventional silicon-(Si-) based power devices, silicon carbide(SiC) power devices have characteristics of lower junction temperature, lower switching losses and higher switching speed. In additional, a performance comparison using Si IGBTs and SiC MOSFETs under different harsh operation conditions is presented. Simulation results show that the maximum junction temperatures and junction temperature ripples of SiC MOSFETs are quite lower than that of Si IGBTs in all test conditions.As a result, the research shows that the junction temperature improvement can be achieved by changing the output current, output frequencies and switching frequencies, and by using new type power device.