Study On Online Junction Temperature Extraction Based On On-state Characteristics Of IGBTs And Its Active Management Methods

The large-scale replacement of traditional fuel vehicles by electric vehicles is an important means to achieve "carbon peaking" and "carbon neutrality".As the core component of electric vehicles,the reliability of the electric drive converter is seriously related to the development of the electric vehicle industry.Studies have shown that load fluctuations such as start-stop,acceleration and deceleration of electric vehicles will cause junction temperature fluctuations in Insulated Gate Bipolar Transistors(IGBTs)and result in mechanical stress between different materials in the IGBT.Degradation of the packaging material or the material interface is induced,which in turn leads to the failure of the IGBT device.The failure of IGBTs is an important reason for the malfunction of the electric drive converter.As a result,it is necessary to carry out research on the extraction of junction temperature of IGBTs for electric drive,and to analyze the relationship between the junction temperature fluctuations behavior and control strategies,which is of great significance to prolong the lifespan of IGBTs and improve the reliability of electric vehicles.Focusing on the active reliability management of IGBT modules in electric drives,the method for calibrating the temperature-sensitive parameters of IGBT devices in electric vehicles is studied based on the motor control model,firstly.Then,according to the physical on-state characteristics of IGBTs,the IGBT junction temperature calculation model that can be fitted by data in a narrow temperature range is deduced.Finally,an active thermal management strategy suitable for smoothing IGBTs junction temperature fluctuations in electric drives is proposed.The main contents of this thesis includes the following aspects:(1)The on-state voltage at load current is a promising method to calculate the junction temperature at present,but it is difficult to calibrate the temperature-sensitive parameters and deal with the mismatch of the calibration relationship due to the aging of the device.Therefore,the thesis firstly summarizes the modeling theory and vector control theory of permanent magnet synchronous motor,and the motor control simulation model is established.The control strategy for generating instantaneous high current in the electric drive is explored,and the use of the current sensor in the electric drive,the Negative Temperature Coefficient(NTC)thermistor sensor integrated in the IGBT module and the external circuit for measuring voltage of the IGBT to calibrate the temperature-sensitive parameters is analyzed.(2)The calibration data generated in the electric drive has a narrow temperature range and cannot fully cover the temperature of the IGBT during operating conditions,which requires better robustness and extrapolation of the model for calculating junction temperature.Therefore,this paper deduces a simplified model of on-state IGBT based on the physical on-state characteristics of IGBTs.And the model proposed exempts material parameters of semiconductor.Compared with the traditional cubic polynomial model,the advantages of the model proposed are analyzed.The reasons for the error of the model fitted with the calibration data of narrow temperature range is discussed,and suggestions for improving the accuracy of junction temperature estimation are given.A 7.5k W experimental platform was built to verify the feasibility of in-car calibration of temperature-sensitive parameters and the accuracy of the proposed junction temperature calculation model.(3)In view of the fact that most of the current active thermal management strategies can only smooth the single working condition of heating or cooling of the IGBT,which is difficult to meet the alternating heating and cooling situations caused by changes in the working conditions of electric vehicles.The thesis attempts to use multiple parameters to jointly smooth the junction temperature fluctuations.Firstly,a simulation model of the electro-thermal coupling of IGBTs is built.Combined with the established motor control model,the variation of junction temperature during operating conditions can be simulated and analyzed.In preparation for evaluating the effect of different active thermal management strategies.,the calculation process of damage degree of the IGBT under operating conditions of an electric vehicle is summarized.Finally,the stator current and the switching frequency are selected as junction temperature adjustment parameters considering the characteristics of motor control.The above two parameters are combined through a double hysteresis loop to form an active thermal management strategy.The proposed strategy can effectively reduce the number of large thermal cycles that seriously affect the lifespan of the IGBT,and significantly improve the reliability of the IGBT.