Analytical Models for IGBT Junction Temperature Estimation

Humphrey Mokom NJAWAH ACHIRI, M.Sc.

Doctoral thesis

Abstract:

A thermal model to accurately estimate the junction temperature of inverters is developed. State of the art methods for determining thermal impedance networks for IGBT modules are used in the establishment of the relationship between the measured transistor or diode voltage and temperature under homogenous temperature distribution across the IGBT module. The junction temperature is recomputed from the established voltage-temperature relationship and used in determining the thermal impedance network. These methods requires accurate measurement of voltage drop across the transistors and diodes under specific designed heating and cooling profiles. Validation of the junction temperature is done using infrared camera or sensors placed closed to the transistors or diodes (in some cases and open IGBT module) so that the measured temperature is as close to the junction as possible. In this thesis we propose an alternative method for determining the IGBT thermal impedance network using the principles of least squares. This method uses measured temperatures for defined heating and cooling cycles under different cooling conditions to determine the thermal impedance network. The results from the proposed method are compared with those obtained using state of the art methods. Based on the calculated junction temperature, an optimal thermal management strategy of the electric drivetrain based on adaptive linear current derating and I2t derating to allow for maximum possible torque and optimum thermal protection of the electric drivetrain is implemented.

Abstract:

A thermal model to accurately estimate the junction temperature of inverters is developed. State of the art methods for determining thermal impedance networks for IGBT modules are used in the establishment of the relationship between the measured transistor or diode voltage and temperature under homogenous temperature distribution across the IGBT module. The junction temperature is recomputed from the established voltage-temperature relationship and used in determining the thermal impedance network. These methods requires accurate measurement of voltage drop across the transistors and diodes under specific designed heating and cooling profiles. Validation of the junction temperature is done using infrared camera or sensors placed closed to the transistors or diodes (in some cases and open IGBT module) so that the measured temperature is as close to the junction as possible. In this thesis we propose an alternative method for determining the IGBT thermal impedance network using the principles of least squares. This method uses measured temperatures for defined heating and cooling cycles under different cooling conditions to determine the thermal impedance network. The results from the proposed method are compared with those obtained using state of the art methods. Based on the calculated junction temperature, an optimal thermal management strategy of the electric drivetrain based on adaptive linear current derating and I2t derating to allow for maximum possible torque and optimum thermal protection of the electric drivetrain is implemented.

Keywords

IGBT Junction Temperature, Analytical Thermal Model, Least Squares Method

Language used: English

Date on which the thesis was submitted / produced: 14. 6. 2022

Accessible from:: 31. 12. 2999

Thesis defence

• Supervisor: Prof. Ing. Zdeněk Peroutka, Ph.D.

University of West Bohemia

Faculty of Electrical Engineering

Doctoral programme / field:
Electrical Engineering and Informatics / Electronics