Unregulated bus operation of server-to-virtual bus differential power processing for data centers

Series-stacking and differential power processing techniques have been proposed for data center power delivery applications in order to drastically increase power conversion efficiency in the server racks. Although above 99% system-level efficiency is achieved in the recent literature for steady-state and hot-swapped operation of the series-stacked servers, reported works required a well-regulated dc bus which may not be compatible with battery backup systems. This paper presents a control method and associated hardware which achieves unregulated bus operation of the series-stacked server power delivery architecture for data centers. The experimental results demonstrate 99.4% system-level power conversion efficiency on a four-server testbed that is energized by a decaying dc bus, verifying the proposed control ideal.