Marco Denk

Online Junction Temperature Cycle Recording of an IGBT Power Module in a Hybrid Car

The accuracy of the lifetime calculation approach of IGBT power modules used in hybrid-electric powertrains suffers greatly from the inaccurate knowledge of application typical load-profiles. To verify the theoretical load-profiles with data from the field this paper presents a concept to record all junction temperature cycles of an IGBT power module during its operation in a test vehicle. For this purpose the IGBT junction temperature is measured with a modified gate driver that determines the temperature sensitive IGBT internal gate resistor by superimposing the negative gate voltage with a high-frequency identification signal. An integrated control unit manages the measurement during the regular switching operation, the exchange of data with the system controller, and the automatic calibration of the sensor system. To calculate and store temperature cycles on a microcontroller an online Rainflow counting algorithm was developed. The special feature of this algorithm is a very accurate extraction of lifetime relevant information with a significantly reduced calculation and storage effort. Until now the recording concept could be realized and tested within a laboratory voltage source inverter. Currently the IGBT driver with integrated junction temperature measurement and the online cycle recording algorithm is integrated in the voltage source inverter of first test vehicles. Such research will provide representative load-profiles to verify and optimize the theoretical load-profiles used in today’s lifetime calculation.

Comparison of counting algorithms and empiric lifetime models to analyze the load-profile of an IGBT power module in a hybrid car

In the recent years various models and counting algorithms to estimate the lifetime of an IGBT power module were publicized. Primarily they differ in the number of parameters used to specify a temperature cycle. Generally a temperature cycle is defined with its amplitude, its absolute temperature and its heating time. In this paper the impact of these parameters onto the lifetime calculation is investigated by analyzing the load-profile of a hybrid car with different empiric lifetime models and cycle counting algorithms. The considered load-profile incorporates active and passive temperature cycles over a time span of one year. It is found, that a cycle specific absolute temperature and also a cycle specific heating time have major influence on the estimated lifetime. Moreover passive temperature cycles contribute noticeable to the module lifetime so that a cycle counting algorithm has to be capable of extracting and parameterizing them correctly. The comparison of established counting algorithms shows, that an accurate cycle extraction demands the usage of a Rainflow algorithm.

Comparison of U CE - and R Gi -based junction temperature measurement of multichip IGBT power modules

The internal gate resistor RGi 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 RGi-based junction temperature measurement and compares it with the widespread UCE-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 RGi-method measures a higher temperature than the area-averaging UCE-method. Especially at steep lateral temperature profiles the RGi-measured temperature is closer to the chip peak temperature than the UCE-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.

Investigation of the characteristic thermal properties of IGBT power modules for robust in-situ health monitoring

This paper investigates the characteristic thermal properties of IGBT power modules and develops a very robust health monitoring concept to identify an aged chip-solder within a voltage source inverter. It is shown that at an optimum excitation frequency the power module structure enables a selective identification of an increased thermal chip-solder resistance Rth, 1 with a maximum Rth, 1 measuring sensitivity. These outstanding features of the thermal power module structure were investigated in the frequency domain and verified by experimental measurements with artificially aged power modules.