Short Course Program
Cosmic ray ruggedness of power electronic devices
Uwe Schilling studied physics at the Friedrich-Alexander-University in Erlangen / Germany. There, he received his Dipl. Phys. degree in 2007 and continued as a PhD student in the field of quantum optics. In 2011, he was awarded the PhD for the doctoral thesis entitled “Measurements in Quantum Optics”. In the same year, he started at Semikron as a reliability engineer in the group of Prof. Dr. Uwe Scheuermann, where his work focused on failure statistics and cosmic ray failures. In 2016, he joined Semikron’s application department, there concentrating his research on the switching behavior of modern silicon IGBTs and freewheeling diodes, and their optimized integration into power modules. However, he also continues his studies of the cosmic ray robustness of power electronic devices.
In the early 1990s, cosmic rays were identified as a root cause for unexpected and sudden failures of power electronic device in the field. As measures that increase the ruggedness towards this failure mechanism typically counteract the electric performance, even modern devices usually display a significant cosmic ray failure rate in the gap between the typical application voltage and their rated blocking voltage. However, two parallel developments continue to make this gap narrower: The design of ultra-low inductive modules allows for less margin between the rated voltage and the application voltage. At the same time, there is an ongoing trend towards higher system voltages to reduce system costs and harvest power loss savings in applications such as photovoltaic inverters, uninterruptible power supplies, and recently even low voltage wind energy converters. Consequently, it remains important that the requirements with respect to cosmic ray ruggedness are accounted for at an early stage of the system design, as there is no “easy way out”, once some key parameters like system topology, DC link voltage, and semiconductor technology have been fixed.
This short course aims at an audience with a general power electronic background and gives a comprehensive overview of cosmic ray robustness of power electronic devices. It begins by introducing the details of the basic physical mechanism and its main dependencies. From there, it moves to accelerated testing of the cosmic ray ruggedness of power electronic devices. Some exemplary results will be presented, among others on the often discussed differences between silicon and silicon carbide semiconductors, or on design measures to increase the cosmic ray immunity. Finally, it is shown how such test results can be used to estimate the cosmic ray failure rate of a representative solar power application and how an understanding of the dependencies of the failure mechanism and the application conditions can help to optimize the system design.