Magnetic Design for High Temperature, High Frequency SiC Power Electronics
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.
Place, publisher, year, edition, pages
Institutt for elkraftteknikk , 2013. , 157 p.
IdentifiersURN: urn:nbn:no:ntnu:diva-22568Local ID: ntnudaim:9216OAI: oai:DiVA.org:ntnu-22568DiVA: diva2:649813
Undeland, Tore Marvin, Professor