PhD Thesis Defense: Andrew Nadler

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"Analysis, Optimization, and Design of Small-Scale Hybrid-Core Inductor Designs that Achieve High Energy Densities and Low Loss"

Abstract

As the size of power converters and other electronics has shrunk over time, miniaturization of passive magnetic components, namely inductors and transformers, has fallen behind. Much of this is due to magnetic scaling laws, which degrade inductor performance at reduced sizes, in contrast to other common power converter components, like transistors and capacitors, which are conducive to construction from smaller parallel cells. This does not mean high performance and small sizes are unachievable with magnetic components, but rather intelligent and creative magnetics design is increasingly critical. Typical inductors utilize a conductive winding wrapped around a magnetic core, with loss occurring in both places. This loss releases heat that sets minimum inductor size and, consequently, peak energy density. However, what often prevents reducing loss, particularly winding loss, are core material saturation limits that set minimum winding turns, since the best low-loss core materials, such as ferrites, have low saturation flux densities while high-saturation-flux-density materials, such as steels, have high core loss.

This work explores two novel hybrid-core-inductor types, a hybrid-steel core and a hybrid-permanent-magnet (PM) core, that achieve small size and increased energy density by strategically utilizing the strengths and mitigating the weaknesses of their core materials. Theory behind these two hybrid-core designs is established with reluctance models, and these models are used in an optimization routine to develop designs and characterize spaces where hybrid cores are most beneficial. Finite element simulation procedures unique to each hybrid core verify designs and refine the reluctance model. Simulation results show a hybrid-steel-core inductor at a frequency of 1.5 MHz in a 1210 package increases energy density over 550% compared to a ferrite-core inductor at the same DC resistance while a hybrid-PM-core inductor increases energy density near 100% at 4 MHz. The successful completion of a proof-of-concept, hybrid-steel-core inductor prototype and a small-scale, hybrid-PM-core inductor prototype in a 1210 package is also discussed, including a new winding construction method using electroplating to form a 3D winding.

Thesis Committee

• Charles Sullivan (Chair)
• Jason Stauth
• William Scheideler
• David Perreault (MIT)

Contact

For more information, contact Thayer Registrar at thayer.registrar@dartmouth.edu.