Real Time Monitoring and Wear Out of Power Modules

Pramod Ghimire

Research output: Book/ReportPh.D. thesis

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Power electronic devices have a wide range of applications from very low to high power at constantly varying load conditions. Irrespective of the harsh operating loads, including both internal and external, an improvement in a performance such as efficiency, power density, reliability and cost for power converter is a continuous research effort. Cost is a design limitation where the tendency is always to increase the rated power for the same price or decrease the price for same rated power.

Satisfying the above mentioned facts, a healthy operation of power devices is essential to meet the expected lifetime of converters. Real time monitoring of power modules is very important together with a smart control and a driving technique in a converter. This ensures to operate the device within a safe operating area and also to protect from a catastrophic failure. Furthermore, the inherent physical parameters that deviate by thermo-mechanical stress need to be identified and also measured during operation. Major stressors for high power multi-chip IGBT modules are identified as maximum junction temperature, temperature cycle, over-voltage, over-current, humidity, vibration etc. In addition, finding a root cause of failure is often difficult after a catastrophic failure.

This thesis proposes an on-state parameter measurement technique which is robust and easy to integrate into existing gate driver technology. The technique is suitable for the application in both normal converter operation and in a mission-profile oriented advanced power cycling test. The measurement technique is implemented in a full scale converter under field oriented test conditions.

Initially, a real time measurement technique and it's implementation in a converter are introduced. A full scale converter is also used as an advanced power cycling test setup, where both power module characterization and field emulated testing are proposed. As temperature is identified as a major stressor, transforming on-state forward voltage drop to die temperature for each individual chip is presented at a nominal rated power level. The wear out is monitored online and also the evolution of degradation in interconnects are studied extensively in order to understand the failure process in high power modules under sinusoidal loading conditions. A number of power modules are tested in active power or thermal cycling for different number of cycles under similar loadings. Afterwards degradation evolutions in each power module are assessed and correlated with the results obtained from the online monitoring. Bond wire and solder fatigue are two major expected low thermal cycle fatigues. A data evaluation theory is proposed to separate two different fatigues in converter operation. A method which automatically re-calibrates each individual device is presented removing the effects from a difference in geometry of a power module. In order to map the degradation distribution, four-point probing results and micro-investigations are presented for aged power modules.

The presented online monitoring technique is implementable in real life applications. The measurement technique is also useful for fast overload protection, replacement of software based models for short overload control, etc.
Original languageEnglish
PublisherDepartment of Energy Technology, Aalborg University
Number of pages110
Publication statusPublished - Dec 2015

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  • Ph.d.-grad

    Pramod Ghimire & Zahra Kardanpour


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