A High-Efficiency 5.5kW Battery Backup Unit for OCP Open Rack V3 Using Partial Power Conversion

Battery Backup Units (BBUs) are key components in modern, AI-centric data centers where uptime, efficiency, and high-power capability are critical. Additionally, BBUs can help to reduce the strain on grid infrastructure, due to their peak shaving capability. This paper presents a highly efficient BBU based on a 5.5 kW DC-DC converter using a partial power concept. The output power can be maintained for a battery voltage from 35 to 62 V according to OCP V3 (50V). A power density of 290 W/inch3 is achieved with a converter size of 75 x 128 x 36 mm while maintaining an efficiency above 99%. A prototype has been built, and experimental results are presented.