Power Characterization of a 1200-V/800-V 22-kVA 30-kHz Unity-Gain Dual-Active-Bridge Converter Prototype

Dual-active-bridge (DAB) converters are crucial for enabling high-frequency operation and providing isolation in applications such as solid-state transformers (SSTs). While unity-gain DAB converters, with input and output voltages matched, are theoretically expected to achieve high efficiency across all power levels with inherent zero-voltage switching (ZVS) ability, the increased stored energies in the device output capacitance (C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oss</inf>) reduce efficiency at low loading conditions because of incomplete ZVS (iZVS). Triple-phase shift modulation provides an opportunity for efficiency improvement and is widely studied for non-unity gain DAB converters. The calculation of duty cycles for TPS scheme in existing literature cannot be applied directly for unity-gain DAB converters. This article aims to provide a simple formula for calculation of duty cycles to ensure minimum peak current for unity-gain DAB converters. The proposed calculation of duty ratios is evaluated experimentally with a 1200-V/800-V 22-kVA 30-kHz DAB converter prototype offering up to 10% improvement of efficiency at light loads and ensuring ZVS at all power levels.