Re-thinking data center power delivery: Regulating series-connected voltage domains in software

In this paper, the fundamental advantages of series-connected voltage domains are briefly discussed in light of existing power distribution architectures for data centers. The key technical challenges of this architecture are addressed; and results from a working prototype system are presented as a proof of concept. In particular, a straightforward software-only solution is presented which eliminates the need for power conversion hardware between the distribution bus and server. Based on power-aware load balancing of web traffic and server frequency, this design is shown to provide adequate voltage regulation for a cluster of four web servers sharing the same line current. Compared with measurements of maximum server performance, the series-connected configuration shows only a minor reduction in net throughput. As a step toward improving system reliability and performance, a hardware supplement for over-voltage protection is presented along with measurements verifying its operation at full server load.