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Dissertation/Thesis Abstract

Transformerless Stacked Active Bridge DC-DC Converters: Analysis, Synthesis and Design
by Zhu, Jianglin, Ph.D., University of Colorado at Boulder, 2020, 171; 28157874
Abstract (Summary)

The increasing power demand in data centers drives the need for high step down dc/dc converters that also offer improved efficiency and power density performance. High conversion ratio dc/dc converters are fundamentally more challenging to design due to the high indirect power requirement. Therefore, “dc transformer” (DCX) converters such as the isolated dual-active-bridge (DAB) and the non-isolated switched-capacitor (SC) converters have been of wide interests.

The fundamental question addressed in this thesis is how to combine the benefits of DA Band SC converters and reproduce DAB converter operating characteristics in non-isolated (transformerless) converters. This work offers an affirmative answer to this question by introducing a new class of hybrid dc-dc converters named Transformerless Stacked Active Bridge (TSAB) converters as an approach to hybridization of conventional SC converters. Generalized analysis, systematic synthesis, design optimization and comparison of TSAB converters are presented.

Features of TSAB converters include soft charging and discharging of capacitors, zero-voltage switching, low peak and root-mean-square (RMS) current stresses, low energy storage requirement of magnetic components, and regulation capabilities using simple phase-shift control. Systematic synthesis allows TSAB converters to be obtained from many well-known SC parent topologies, including Dickson, ladder, stacked-ladder, doubler, and Fibonacci. Experimental results are summarized for 48-to-12 V doubler, 48-to-12 V Dickson, and 36-to-12 V ladder TSAB prototypes. It is shown how the TSAB prototypes use small ac inductors (10’s to 100’s of nH) while operatingat relatively low switching frequencies (150-200 kHz) and have measured efficiency above 98% overwide load range. Additionally, it is shown how TSAB converters can be merged with the follow-upregulation stage for point-of-load (PoL) applications. 94% peak efficiency is demonstrated in a 48 Vto 0.8-1.8 V, 100 A prototype.

Indexing (document details)
Advisor: Maksimovic, Dragan
Commitee: Erickson , Robert W., Le, Hanh-phuc, Poveda, Jorge I., Seo, Gabsu
School: University of Colorado at Boulder
Department: Electrical Engineering
School Location: United States -- Colorado
Source: DAI-A 82/6(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Electrical engineering, Design, Management, Industrial engineering, Electromagnetics, Energy
Keywords: Data Center (DC), DC transformer, DC-DC converter synthesis, DC-DC converter topologies, Hybrid converters, Power density performance, Dual-active-bridge (DAB), Switched-capacitor (SC) converters, Zero-voltage switching
Publication Number: 28157874
ISBN: 9798557024457
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