Study On Lifetime Evaluation Of IGBT Modules Based On Transient Thermal Impedance

Power electronic converters have been widely used to provide high quality and high efficiency electrical energy,primarily due to their superior performance in terms of conversion,transimission and control of electrical energy.As the key component of converters,the reliability of Insulated Gate Bipolar Transistor(IGBT)modules is an important guarantee for the safety and stability of systems.Attributing to harsh working environments and multilayer structure of module packaging,solder layers are easy to crack and delmenate,which will lead to the failure of IGBT modules.The failures of IGBTs are responsible for a significant proportion of overall system faults.Proposing effective method to evaluate fatigue stage of solder layers and improving performance of lifetime estimation models are significantly help to improve the system availability and lower maintenance cost.Currently,it is difficult to respectively quantify fatigue degrees of chip and DBC solder layers.And,lifetime estimation models do not consider the effects of fatigue accumulation,which result in overestimate.According to the transient thermal responses of IGBT module with different fatigue stages,an effective method to identify failure point and respectivley quantify fatigue degrees of chip and DBC solder layers is proposed.Then a thermal network updata strategy considering specific degenerate solder layer is proposed.Finally,a lifetime estimation model considering the fatigue accumulation of solder layer is established.Validation experiments are carried out to demonstrate those models.The main research contents of the thesis are shown as follow:(1)An multi-physics field coupling model,in which the temperature dependence of power loss and mechanical viscoplasticity of solder material are taken into account,is built.The failure mechanism of the solder layer and the thermal-mechanical properties of IGBT module with chip or DBC solder layer fatigue are discussed by utilizing the multi-phyisics field coupling model.It found that transient thermal impedance includes more information of solder fatigue.(2)Based on the thermal response characteristics of IGBT moduel with different fatigue stages,an effective method for identifing failure position and quantifing failure stage of DBC and chip solder layer is proposed.Firstly,the variation regulation of transient thermal impedance of IGBT with different solder layer fatigue is discussed.Then,an experimental platform is designed and built to validate the feasibility and effectiveness of the proposed method.The results indicate that the separation point of the transient thermal impedance can be used to identify the failure point of the solder layer.And,building a proper Cauer thermal network model,in which failure information of each layer are divided into different order,can respectively quantify failure stages of chip and DBC solder layer.(3)The effects of solder layer fatigue on thermal profiles are neglected in some existing lifetime estimation models,which will seriously exaggerate lifetime of IGBT module.In this part,a thermal network update strategy and lifetime estimation model considering the positive feedback of solder degradation on failure,are proposed.Firstly,the differences of effects of chip or DBC solder layer fatigue on thermal performance are investigated.It is concluded that operation frequency and degradation degree of module have impacts on the differences.Then,an update strategy based on Cauer thermal network is proposed.Comparison with the existing update strategies is made to verify the proposed strategy.Lastly,the update strategy is applied to improve lifetime estimation model.