A four-level dual active bridge converter for data center applications

Abstract

The Dual Active Bridge (DAB) bi-directional DC/DC converter is a popular topology originally designed for energy storage applications. It has high efficiency, galvanic isolation, and, most importantly, controllable power flow. However, for high voltage conversion ratio applications, there are challenges on switch stress and component size. In this work, we are replacing the half bridges on the primary side of the original DAB with Flying-Capacitor Multi-Level (FCML) topology using Phase-Shifted Pulse Width Modulation (PS-PWM) control scheme. While the original benefits are still available, the voltage stress across each switch is reduced, enabling the use of faster GaN switches that also have smaller drain-to-source turn-on resistance. The increased switching frequency at the AC node also decreases the size of the auxiliary inductor. The theory of operation and the simulation result of the new topology will be discussed. Then, the initial measurements from an experimental prototype are presented. The hardware prototype demonstrates the converter topology's ability to maintain a steady voltage output for a varying load at a high voltage conversion ratio and a large voltage input.