Appendix A Soft-Switched DC-DC Converter

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Title Magnetic materials and soft-switched topologies for high-current DC-
DC converters
Author(s) Rylko, Marek S.
Publication date 2011
Original citation Rylko, M. S. 2011. Magnetic materials and soft-switched topologies for
high-current DC-DC converters. PhD Thesis, University College Cork.
Type of publication Doctoral thesis
Link to publisher's http://library.ucc.ie/record=b2015003
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Rights © 2011, Marek S. Rylko.
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Magnetic Materials and Soft-Switched Topologies
for High-Current DC-DC Converters

Marek S. Rylko M.Sc., B.E.
A thesis presented to the National University of Ireland for the
degree of Doctor of Philosophy
January, 2011
Supervised by Dr. John G. Hayes and Dr. Michael G. Egan
Department of Electrical and Electronic Engineering
University College Cork
Ireland
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A good scientist is a person with original ideas. A
good engineer is a person who makes a design that works
with as few original ideas as possible.
Freeman J. Dyson

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Abstract
This thesis is focused on the comparison and selection of magnetic materials for high-
power non-isolated dc-dc converters for industrial applications or electric, hybrid and fuel
cell vehicles. The application of high-frequency bi-directional soft-switched dc-dc converters
is also investigated.
The thesis initially outlines the motivation for an energy-efficient transportation system
with minimum environmental impact and reduced dependence on exhaustible resources. This
is followed by a general overview of the power system architectures for electric, hybrid and
fuel cell vehicles. The vehicle power demand, power sources, and general dc-dc converter
topologies are discussed. The dc-dc converter components are then discussed with emphasis
on recent semiconductor advances.
A novel bi-directional soft-switched dc-dc converter with an auxiliary cell is
introduced in this thesis. The soft-switching cell allows for the MOSFET’s intrinsic body
diode to operate in a half-bridge without reduced efficiency. A mode-by-mode analysis of the
converter is performed and closed-form expressions are presented for the average current
gain of the converter. The design issues are presented and circuit limitations are discussed.
Magnetic materials for the main dc-dc converter inductor are compared and
contrasted. Novel magnetic material comparisons are introduced, which include the material
dc bias capability and thermal conductivity.
An inductor design algorithm is developed and used to compare the various magnetic
materials for the application. The area-product analysis is presented for the minimum
inductor size and highlights the optimum magnetic materials.
Finally, the high-flux magnetic materials are experimentally compared. The practical
effects of frequency, dc-bias, and converter duty-cycle for arbitrary shapes on flux density,
air gap effects on core and winding, the winding shielding effect, and thermal configuration
are investigated.
The thesis results have been documented at the IEEE EPE conference in 2007 and
2008, IEEE APEC in 2009 and 2010, and IEEE VPPC in 2010. A journal paper has been
accepted for publication in 2011 by the IEEE Transactions on Power Electronics.
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Acknowledgements
This thesis would not have been possible without the guidance and the help of several
individuals who in one way or another contributed and extended their valuable assistance in
the preparation and completion of this study.
First and foremost, I would like to thank my academic advisors Dr. John Hayes and Dr.
Michael Egan for their encouragement, guidance, friendship, expertise, patience and
enthusiasm over the last six years. I wish to thank Prof. Andrew Forsyth and Dr. Kevin
McCarthy for examining my thesis.
I wish to thank Dr. Richard Kavanagh whose support made my study at UCC possible.
The financial support of the EU Marie-Curie Fellowship programme and further technical
and financial support of General Motors are greatly appreciated.
It is difficult to list all individuals who contributed to my work, but I wish to thank
George Woody, John Hall, Steve Hulsey, Terry Ward and Dan Kowaleski in California for
their motivation, valuable advices and friendship.
I am indebted to my many colleagues and the staff from Power Electronics Research
Laboratory and UCC for support me through past years. Among the many contributors are
Jason Hannon, Kevin Hartnett, Dr. Brendan Lyons, James Griffiths, Dr. Ray Foley, Dr.
David Cashman, Donal Murray, Naveen Boggarapu, John Slowey, Dr. Richard Morrison,
Daithi Power, Dr. Dara O’Sullivan, Judy Rea, Gerry McCarthy, Sarah Babbington, Geraldine
Mangan, Rita Sarteschi, Tim Power and Michael O’Shea.
I wish to thank all Marie Curie Fellows for a great time together, support and valuable
discussions.
The support of my family and friends has been ever so important to the success of my
work. I want to thank Artur, Beata, Benjamin, Jana, Kasia and Hubert, Kinga, Krzysiek and
Justyna, Magda, Monika, Nicole, Piotr. Please forgive me of not listing all of you.
Finally, I owe my deepest gratitude to my parents Zdzisław i Irena and brother
Wojciech for their love, encouragement, continuous support and patience.

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List of Publications
Journal Paper:
1. M.S. Rylko, B.J. Lyons, J.G. Hayes, M.G. Egan, “Revised magnetics performance
factors and experimental comparison of high-flux materials for high-current dc-dc
inductors,” IEEE Transactions on Power Electronics, 2011, in press.
Conference Papers:
1. M.S. Rylko, J.G. Hayes, M.G. Egan, “Experimental investigation of high-flux
density magnetic materials for high-current inductors in hybrid-electric vehicle dc-dc
converters,” IEEE Vehicle Power and Propulsion Conference, 2010, pp. 1-7 .
2. K.J. Hartnett, M.S. Rylko, J.G. Hayes, M.G. Egan, “A comparison of classical two
phase (2L) and transformer — coupled (XL) interleaved boost converters for fuel cell
applications,” IEEE Applied Power Electronics Conference, 2010, pp. 787-793.
3. M.S. Rylko, K.J. Hartnett, J.G. Hayes, M.G. Egan, “Magnetic material selection for
high power high frequency inductors in dc-dc converters,” IEEE Applied Power
Electronics Conference, 2009, pp. 2043-2049.
4. M.S. Rylko, B.J. Lyons, K.J. Hartnett, J.G. Hayes, M.G. Egan, “Magnetic material
comparisons for high-current gapped and gapless foil wound inductors in high
frequency dc-dc converters,” IEEE EPE-PEMC, 2008, pp. 1249-1256.
5. M.S. Rylko, M.G. Egan, J.G. Hayes, D. Power, “A soft-switched bi-directional dc-dc
converter,” IEEE European Conference on Power Electronics and Applications,
2007, pp. 1-10

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