Aidan Mac Phillips, M.S.
University of Pittsburgh, 2020
This thesis was presented
by
Aidan Mac Phillips
It was defended on
July 13, 2020
and approved by
Dr. Brandon Grainger, PhD., Assistant Professor, Department of Electrical and Computer Engineering
Dr. Alan George, PhD., Professor, Department of Electrical and Computer Engineering
Dr. William Stanchina, PhD., Professor Emeritus, Department of Electrical and Computer Engineering
Thesis Advisor: Dr. Brandon Grainger, PhD., Assistant Professor, Department of Electrical and Computer Engineering
ABSTRACT
Gallium Nitride (GaN) devices show particular promise for space-rated power conversion applications that rely on MOSFET technology whose performance is severely limited by the radiation hardening processes. Though GaN failure mode classification and radiation hardened device variety is limited, the current space-rated selection pool can still yield significant efficiency and power density improvements. However, the context of GaN research is often future oriented such that the application of GaN to common, proven, space-rated converter designs are rare.
The presented work quantifies the performance benefits of market available, space-rated GaN HEMTs over radiation hardened MOSFETs for a synchronous forward converter, which remains an extremely popular topology for isolated, medium power, DC-DC conversion on NASA satellite systems. Two 75-Watt, space-rated forward converters were designed, implemented, and benchmarked, with the power switch technology being the single variable of change. By forming pareto-optimal fronts of the key device metrics, optimal Rad-hard MOSFETs were chosen so that the baseline converter performance was considered best-case.
The frequency limitations of common, available, Rad-hard PWM controllers limited power density in the GaN and Si converters alike, however, efficiency gains proved sizeable. The GaN based converter saw a peak efficiency of 86%, which was a 4.54% improvement over the Si baseline. Detailed efficiency and loss differential plots are presented which show the GaN converter’s reduced sensitivity to input voltage. Extreme similarity between the waveforms and functional characteristics of the two converters verified the design of the experiment. Furthermore,the performance of the baseline Si converter proved very similar to that of a large sampling of space-rated forward converters, making the experimental results have a high degree of utility for manufacturers.
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