Modelling The Electro-Thermo-Mechanical Multi-physics Coupling Model For Press Pack IGBTs

The capacity and reliability of power electronic deivces for the key equipments used in the flexible High Voltage Direct Current transimission(HVDC)system with its rapid development encounter great challenges,especially the Modular Multi-level Converter(MMC)valve and HVDC breaker.Compared to the wire-bonded high power Insulated Gate Bipolar Transistor(IGBT)modules,press pack IGBTs is quite suitable for the high voltage and high power density applications,such as the power system,with its advantages of double side cooling,easy to connect in series,high power density and Failure Short Circuit Mode(FSCM)and so on.The physics field of press pack IGBTs is very complex which is coupled with the electrical,thermal and mechanical fields.The physics variables of each field are coupled with each other.The power density and reliability improvement of press pack IGBTs will be strictly resticted without the clear cognition of the change trend of those physics variables.Focusing on the scientific issues and key technical difficulties existing in the packaging process of press pack IGBTs,the direct co-coupling relationship among the electrical,thermal and mechanical fields within press pack IGBTs,calculation method and experiment method are studied in this paper.The purpose of this paper is to build up an electro-thermo-mechanical multi-physics model which is able to reflect the real physics phenomena within press pack IGBTs to predict the coupling mechanism of the physcis variable in each field.Firstly,the mechanical model and the coupling relationship between physics fields are analyzed according to the packaging style of press pack IGBTs.And then some experiments are excuted to verify the validation and accuracy of those finite element models.Furthermore,the finite element models are also refined based on the experimental results.At the same time,the coupling variable of mechancial and thermal fields is studied.According to the application requirements,two different coupling calculation methods are proposed in this paper,and the electro-thermo-mechanical multi-physics three dimensional coupling model and field-circuit coupling model are established.For the finite element models,an accurate mechanical model and the model to get the couping variable between the mechanical field and thermal field are built.And the coupling mechanism and change trend of each physics variable are thoroughly studied.Furthermore,the simulation results are verified by the experimental results.The multi-physics model of the single silicon chip submodule is also established based on those models mentioned before.It lays the foundation for establishing the electro-thermo-mechanical multi-physics coupling model of press pack IGBTs.Two calculation methods are proposed to apply in the three dimensional field model and field-circuit model to predict the coupling mechanism of the submodule.For the experiment methods,the thermal structure function method is proposed in this paper to measure the thermal contact resistance among the components within press pack IGBTs accurately to verify the validation of the coupling variable between the mechanical field and thermal field.The measurement limitation caused by the speicial packaging style and working condition of the press pack IGBTs is overcame.And furthermore,the change trend is also obtained by this method.At the same time,the transient dual interface method is also proposed in this paper to accurate measure the junction to case thermal resistance of press pack IGBTs to verify the validation of the multi-physics model of the single chip submodule.Not only the measurement limitation of the thermocouple caused by the external clamping force is overcame but also the errors caused by the thermocouples which is inevitalbe is also eliminated.The method proposed in this paper fills the blank of the measurement of junction to case thermal resistance of press pack IGBTs and improves the accuracy.The electro-thermo-mechanical multi-physics three dimensional coupling model and field-circuit coupling model are established based on the differences of the press pack IGBTs used in converter valve and HVDC breaker.The coupling mechanism and change trend of physics variables within press pack IGBTs with different applications are stuided based on the multi-physics models.The research results show that the coupling relationship among the physics variables within press pack IGBTs used in the converter valve is very strong.The imbalance of one physics variable among chips within press pack IGBTs will affect other physics variables significantly,especialy the clamping force distribution.However,the coupling relationship among the physics variables within press pack IGBTs used in the HVDC breaker is much weaker and the distribution of each physics variable among silicon chips within press pack IGBTs is also relatively uniform,for example the junction temperature.