Research On Junction Temperature Calculation And State Evaluation Method Of IGBT Module

The coefficient of thermal expansion mismatch between IGBT layers,and the temperature fluctuation in procession of work would cause internal connection is subjected to different thermal mechanical stress,which will lead to IGBT module aging.Therefore,the accurate calculation of IGBT junction temperature and the evaluation of aging state have important significance to improve the reliability of IGBT module.The IGBT module is studied in the aspects of its failure mechanism,power calculation,junction temperature calculation and aging state evaluation.Firstly,the failure mechanism of IGBT is analyzed,and the main causes of fatigue failure of the bond wire failure and solder fatigue is the coefficient of thermal expansion mismatch between IGBT layers and temperature fluctuation in the working process.Thus,the theoretical basis for establishing the electro-thermal model and evaluating the aging state is provided.Secondly,the building process of power loss and thermal network of IGBT module is introduced in detail using the three-phase bridge inverter for example.Then the electro-thermal simulation model for SPWM inverter IGBT module is built.The simulation results show that the junction temperature of IGBT or FWD is periodic fluctuation,and the wave mean of junction temperature stability to a constant value after a short time rising.Thirdly,the?T_c power cycle accelerated aging test of IGBT module is carried out.The three dimensional relation surface of IGBT saturation voltage with junction temperature and collector current,transient thermal impedance curve and switching loss are measured every 1000 power cycles,and the changes of electro-thermal parameters under different power cycles are studied.Experimental results demonstrate that IGBT electro-thermal parameters increase more quickly with the aging process of module under the same conditions.After 6000 power cycles,the IGBT saturation voltage,threshold voltage,conduction resistance,turn-on loss,turn-off loss and thermal resistance are increased by4.14%,4.18%,4.21%,12.01%,18.87%and 22.65%respectively.There is no significant change in the relationship between IGBT saturation voltage,junction temperature and collector current under different power cycles,so saturation voltage can be used as the state parameter to evaluate the aging state of IGBT module.Fourthly,electro-thermal model of IGBT module under power thermal cycles are built by change electro-thermal parameters,and the influence of various parameters of the electro-thermal model on the junction temperature are analyzed respectively.Then,the effect of IGBT module aging on the junction temperature calculation accuracy of electro-thermal model is studied.Finally,the electro-thermal model considering IGBT module aging state is proposed.The results show that the junction temperature gradually increased with the IGBT module aging under the same conditions,and the relative temperature rise is 37.39%and relative temperature variation is 15.61%after 6000 power thermal cycles.Therefore,the junction temperature calculation accuracy of electro-thermal model is gradually reduced,and the junction temperature of IGBT module can be more accurate calculated by electro-thermal model considering IGBT module aging state.