Design and evaluation of a reconfigurable stacked active Bridge dc/dc converter for efficient wide load-range operation

Abstract

This thesis presents the design and implementation of a step-down soft-switched dc-dc converter based on an active bridge topology which overcomes some of the limitations of the conventional dual-active bridge (DAB). The topology comprises a double-stacked bridge inverter, coupled to a recongurable rectifier through a special three-winding leakage transformer. The converter can run in a low power mode that greatly increases light-load efficiency by reducing core loss and extending the zero-voltage switching (ZVS) range. The converter is implemented with a single compact magnetic component, providing power combining, isolation, and energy transfer inductance. The theory of the converter and its various operating modes, referred to in this thesis as the Double-Stacked Active Bridge converter, is also explored, and a magnetic model of the special three-winding transformer and leakage inductance is presented. The target application is for 380 V dc distribution systems for data centers, where the converter operates for the majority of the time at the nominal input voltage, but must have high eciency over a wide load range. A 175 kHz, 300 W, 380 V to 12 V prototype converter achieves 95.9% efficiency at full load, a peak efficiency of 97.0%, an efficiency above 92.7% down to 10% load and an efficiency above 79.8% down to 3.3% load.