Research On Fatigue Life And Thermal Stress Recurrence Of Power Electronic Devices Used In Electric Vehicle Converters

Recently,power shortages and environmental pollution have become prominent issues that plague China’s automotive industry.Electric vehicle is the the inevitable choice to continue the development of automobile industry in the future,which has a broad space for development.The converter is a key part of electric vehicle.However,it is also one of the most fragile components according to probability distribution of fault,and the failure of the converter is largely attributed to the failure of insulated gate bipolar transistor(IGBT).Therefore,the life prediction and timely replacement of power modules,the exploration of thermal control scheme of power devices,the optimization of converter operation and design can effectively improve the reliability of electric vehicles.Electric coupling thermal network model of power module generally ignores the multi-chip thermal coupling effect under the compact package.Most of the existing power device life prediction method is based on the cold and hot cycle tests under a certain temperature range,which is out of the practical application scenario.In this paper,the power devices used in the electric vehicle converter are selected as the research object.The multi-chip coupling thermal network based on the transient thermal impedance response method is established,and the service mileage of the power device under the practical working conditions is quantified.Next,putting forward the thermal control strategy to improve the reliability and lifetime of the power device and reduce the junction temperature fluctuation of the power device as well as extend the life of the device.Finally,thermal behavior testing platform for power devices is set up,and the thermal behavior under actual operating conditions is revealed.The main research contents of this paper are shown in the following:1)Based on the transient thermal impedance response method,the whole thermal network model of inverter,including IGBT power module and heatsink,is established.The self-heating and cross-coupling effect inside the multi-chip power module is fully considered.By introducing the theory and evidence,the thermal impedance difference of different size chips is explored.The temperature dependence of material thermal properties(the thermal conductivity and specific heat capacity)and the nonlinear problems of thermal model due to the three-dimensional thermal convection of heatsink is evaluated.The correlation between the partial parameters of thermal network and the boundary conditions,such as ambient temperature,heat dissipation condition and power loss,is found.2)Considering the sensitivity of device switching behavior to the system configuration,switching power loss of different bus voltages,junction temperature and current are tested by double pulse test method under the actual application scenario.The electro-thermal coupling model of power module is established,and the junction of IGBTs is obtained under the actual driving cycle profile.The lifetime of power device is predicted by means of rain flow counting algorithm and fatigue damage criterion.The influence of the related factors such as ambient temperature,operating condition and fatigue accumulation on the lifetime prediction results is mastered systematically.3)Based on a simplified IGBT power loss analysis model,the influence of different gate driving voltages on IGBT switching loss is analyzed and discussed,and a new idea is put forward to realize the control and regulation of power loss and junction temperature by using gate driving voltage adjustment.The essence of the proposed junction temperature tracking control strategy is to adjust the switching performance of the device,which can realize the real-time control of the device power loss.Thus,it will restrain the fluctuation of junction temperature and slow down the aging of the device,and extend the life of the device.Finally,the control strategy of junction temperature tracking is verified by the experimental test.4)The construction of power device stress recurrence platform includes the design of the main circuit,the control system and the software system.Firstly,aiming at the stress testing requirement of IGBT module,this paper analyzes the system transfer function of main circuit,clarifies the system control scheme of the platform,and designs electrical parameters of components for the stress testing platform in detail.Finally,the junction temperature profile of power device under the actual operation condition is tested.