Power Electronics

Data Centers Will Test Digital Power's Mettle

As digital power technology continues to develop, the industry continues to debate and discuss how, why and where the technology will have its greatest impact. At the recent Digital Power Forum (DPF) in Dallas, much of the discussion pointed to the data center as the answer to the “where” question, while making a case for “why” digital power control and power management techniques are needed there.

Several speakers at the forum discussed how increasing server density is driving up power demands within the data center, while also making it more difficult to cool. The maximum load in a typical 42U cabinet has risen from the kilowatt level in the days of the 5U server to about 25 kW in the same rack populated with blade servers. And it's probably going to get worse. In his presentation at the DPF, Geof Potter of Astec/Artesyn observed, “Energy consumption in data center server racks is on a trajectory toward 40 kVA.”

As companies fill their data centers with thousands of servers, the total energy consumption of the data center is becoming a critical issue. Another DPF speaker, David Douglas of Sun Microsystems, commented, “Over 70% of data centers are out of space, power or cooling.” And the issue is hitting IT companies in their wallets. “Power is now upwards of 20% to 25% of many IT budgets,” said Douglas. And even when you drill down to the server level, energy costs become a dominant issue. As Potter observed, “Often the cost of operating each rack-mounted server exceeds the cost of the server itself on an annual basis.”

Energy costs are already influencing data center planning in a big way with IT companies locating their newest facilities in areas that offer cheap electricity. Witness the construction of massive data centers by Google, Microsoft and Yahoo near hydropower plants along the Columbia River.

Although the server is at the heart of the power/energy problem, the challenge of delivering power is complicated by the complexity of the power system. Within the data center power system, there are multiple utility feeds, UPSs and generators for reliability; power distribution cabling and equipment; ac-dc power supplies; and then dc-dc converters within the server equipment. Through all these stages of power conversion and distribution there are losses. Then too, fans and cooling units add to the server loads.

In the end, to deliver 1 W to the server, you may have to put about 2 W into the system.

Given the complexity of the data center and its power system, there's no one magic bullet that will drive energy consumption way down and power efficiency way up. Power and cooling problems will need to be attacked from many different angles. For example, some DPF speakers advocated a change from ac to dc power distribution for reduced power consumption and heat generation. Others discussed the need for more efficient processors and servers. And fortunately for the power electronics industry, digital power technology has a big role to play.

As Potter noted, digitally controlled power supplies can help in three areas. These supplies can adapt dynamically to operating conditions to maximize their own efficiency; optimize server operation by changing operating speeds on the fly; and control rack-cooling equipment to maximize cooling efficiency.

To fully exploit digital power technology in the data center, there needs to be a standard interface for communications between the power supplies and the rest of the system. At the moment, server systems are employing a number of interfaces for communicating power-related data. But there is a great deal of momentum behind PMBus now that both IBM and Intel recently announced their support for the PMBus protocol.

Though industry battles over communications standards are likely to continue, the growing support for PMBus is a welcome trend, as it should foster adoption of new digital power controllers and modules. Once designed into advanced servers, digital power components will demonstrate whether they can truly help alleviate the power and cooling crisis in the data center. And what happens there will influence power design in nearly all applications.

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