Magnetic Design for High Temperature,
High Frequency SiC Power Electronics
Torbjørn Sørsdahl
Norwegian University of Science and Technology
Department of Electric Power Engineering
1 Summary
Power electronic components which can operate at high temperatures would benefit a large number
of different applications such as in petroleum exploration, aviation and electrical vehicles. Silicon
carbide semiconductors have in the recent years been introduced commercially in the market. They
are opening up new possibilities to create high temperature devices, due to its superior properties
over silicon. Design of high temperature magnetic components is still a tedious process compared to
normal temperature levels due to little information and software to simplify this process.
The purpose of this thesis is to develop analytical software for high frequency magnetic design in the
temperature range from 130°C, and up to 200°C. Care has been taken into developing temperature
dependent loss models and thermal design. The software is primarily for inductors, but most of the
theory and discussion are also valid for transformers. Prototypes have been built and tested against
the software predictions and good correlation has been observed.
A brief introduction to magnetic materials that can be used at elevated temperatures have been
included focusing on powder cores and ferrites, since other high frequency materials could not
operate at 200°C. It was found that for most materials, it is the laminations and binder agents that
introduce the temperature limit. Materials are designed for specific temperatures which make it
likely that when there is a larger commercial interest for higher temperatures, new materials will be
developed. Core characterization of ferrites and powder cores was performed with a Brochause steel
tester up to 10 kHz, and the losses up to 100 kHz were measured using an oscilloscope and amplifier
approach. The characterization was performed at 20°C 108°C and 180°C.
The measurements show that the analytical loss data provided by the manufacturers underestimates
the losses in Sendust and MPP materials, while there is a good correlation in High Flux, R-ferrite and
N27. New Steinmetz parameters were calculated for MPP and Sendust for 20 kHz. Temperature
primarily influences only Sendust up to 180 °C by a factor of 10-20 %, the little temperature
dependence is in powder cores due to very high curie temperature.
Winding configurations have been investigated, and Litz wire for 200°C do not seem to exist
commercially at this date, however wire for 130°C was successfully used in several 180°C
experiments, but permanent degradation was observed in wires which had been exposed for several
hours. It was found that the insulation in enamel coated round conductors have problems at
elevated temperatures under the rated temperature in the areas where the wire was bent, this was
not observed in Litz wire.
It has been shown that parallel connection of smaller powder cores can in some cases be used to
obtain smaller designs with better thermal dissipation than with a single core. Leakage capacitance
has been measured in several designs and by inserting an air gap between layers the capacitance was
reduced in the same order as a Bank winding.
Output filter for dv/dt, Sinus, and a step down converter have been calculated and built. The step
down filter has been tested in a buck converter, and compared to analytical data.
LINK
https://pdfs.semanticscholar.org/cd3d/67fc303646f9e09b5d16c9d486a0790090f1.pdf
