Research On Reliability Of IGBT Module In Electric Vehicle Inverter

The electric vehicle drive system inverter is an important part of the electric vehicle control system,and the IGBT module is the core power switching device of the electric drive inverter,its reliability is critical for the electric drive inverter and even the entire electric vehicle.In electric vehicle operating conditions,the IGBT module carries intermittent electrical stress because of the randomness and fluctuation of operating speed.Due to the power loss inside the module,the junction temperature will also fluctuate violently,which leads to the electro-thermal cycles stress of each package structure inside the module.The IGBT module will degenerate rapidly due to the continuous electric and thermal stress impact,and the degradation information is contained in the electrothermal characteristic parameters.Therefore,it is of great theoretical and practical value to study the thermal characteristics,test methods,degradation laws and reliability evaluation of IGBT modules.In order to study the reliability of the IGBT module of the electric drive inverter,the main work is as follows:(1)Theoretical,simulation and experimental research on the failure mechanism of IGBT modules for electric vehicles.The structure and working characteristics of IGBT chips are analyzed,then the failure mechanism of IGBT modules is explained.The multi-physics coupling failure is comprehensively analyzed,and the degradation information of the electrol-thermal characteristics contained in the fatigue of module is pointed out.The simulation model of electric vehicle inverter system and IGBT module thermal simulation model are constructed to simulate the electrothermal characteristics such as junction temperature and case temperature of IGBT module under electric vehicle operating conditions.The competitive failure mechanism of chip,bond and solder is analyzed.The accelerated degradation test is designed and carried out based on the thermal cycling characteristics determined by electric vehicle operating conditions,and ultrasonic testing of the chip,bonding and solder of the failed module is carried to determine the failure mechanism.(2)Experimental study on steady-state electrical characteristics of IGBT modules based on saturation voltage drop.The saturation voltage drop and temperature-sensitive characteristics of the IGBT module are analyzed theoretically from the view of physical mechanism,and the effects of packaging damage on the saturation voltage drop are studied.The saturation voltage drop temperature-sensitive characteristic test is designed to test the saturation voltage drop under different collector currents and junction temperatures.The saturation voltage drop degradation model is established based on the accelerated degradation experiment,the degradation law of the saturation voltage drop degradation model under different collector current and junction temperature.(3)Experimental study on transient thermal characteristics of IGBT module based on thermal impedance.The transient thermal impedance and thermal network model of IGBT module are analyzed theoretically.The thermal characteristic test is designed to obtain the transient thermal impedance curve of IGBT module based on the transient double-interface method.The structure function theory is described and the structure functions are constructed to identify the encapsulation structure of IGBT module and simplify the thermal network model.Based on the accelerated degradation test to study the IGBT module transient thermal impedance and thermal network model parameter degradation laws,and then IGBT module crust thermal resistance degradation model is established.The structural function is used to identify the damage location of the IGBT module package,and then the fatigue damage degree of the solder layer is analyzed,and the thermal resistance degradation model of the thermal solder layer of the IGBT module is established.(4)Research on the reliability of IGBT modules under EV operating conditions based on the degradation of electro-thermal characteristics.Build electric vehicle drive system simulation model and IGBT module electro-thermal coupling model to study the influence of degradation of electro-thermal characteristics on IGBT module junction temperature,case temperature and power loss under urban working conditions;make statistics on junction temperature load spectrum under IGBT module working conditions Based on the cumulative damage theory and life model,the influence of the degradation of electrothermal characteristics on the life of the IGBT module is analyzed.