DC power distribution for server farms

By E.C.W. de Jong & P.T.M. Vaessen, KEMA

Summary

Data centers, also known as server farms, are already storing most of the world’s digital information. The availability of this data is of crucial importance to data center customers as an unreliable data service will not survive the fierce competition. A reliable power supply and distribution architecture immediately draws the attention in this regard. Furthermore, data centers consume large amounts of electrical energy in trying to keep up with the energy demand associated with the rapid performance increase of the server technology itself. However, increasing energy prices and political pressure are forcing data centers to re-evaluate their energy consumption and increase their electrical efficiency to remain profitable as well as to adhere to possible environmental legislation.

This paper investigates the reliability and efficiency of an AC power distribution architecture found in typical data centers. The application of a DC power distribution architecture is then proposed as an efficient method of power delivery within a data center. This concept is inspired by the absence of reactive power, the possibility of the efficient integration of small-distributed generation units and the fact that, internally, all the loads operate using a DC voltage. A comparison is then made between the AC and DC power distribution architectures as regards reliability, efficiency and their susceptibility to introducing emerging technologies for supporting on-site electrical power generation and storage to achieve a more sustainable system with less emissions.

The investigation reveals that the reliability and the efficiency of a typical power distribution architecture can be improved by decreasing the number of power conversions required within the crucial current path from the source (public grid) to the load (server card). Yet, reducing the power conversions as far as a single point of conversion has an adverse effect. The reliability is reduced as it makes the power distribution more vulnerable to failure. Implementing a redundant distribution architecture solves this vulnerability. In this regard the DC power distribution architecture has the most advantage as it only requires two power conversions as opposed to four for an AC power distribution architecture. Efficiency improvements ranging from 10 to 20% have been reported in the literature. Furthermore, it has been found that DC power distribution has the most advantage for the connection of emerging technologies for on-site power generation and energy storage as a significant amount of this equipment delivers power in DC or high frequency AC, which requires an intermediate DC conversion when connecting to a conventional AC distribution system.