Comparison of UCE- and RGi-based junction temperature measurement of multichip IGBT power modules

The internal gate resistor R_Gi of an IGBT power module is the most promising temperature sensitive electrical parameter for real-time junction temperature measurement in a working voltage source inverter. This paper investigates R_Gi-based junction temperature measurement and compares it with the widespread U_CE-method that is used for device characterization in laboratory setups. It is found that both methods have similar averaging properties when measuring the junction temperature of paralleled IGBT single chips. However, in case of a centered internal gate resistor the R_Gi-method measures a higher temperature than the area-averaging U_CE-method. Especially at steep lateral temperature profiles the R_Gi-measured temperature is closer to the chip peak temperature than the U_CE-measured one. This deviation is investigated in thermal equilibrium and during the cooling down process using thermal impedance measurement, an IR-camera and a finite element simulation.