High-Voltage DC Distribution Improves Data Center System Efficiency

With soaring Internet traffic, surging mobile voice, video, and data communications, and newly-emerging cloud services, the need for data centers and telecom servers/systems is rising at an alarming rate. Meeting this demand by adding or expanding data centers and servers will place an enormous burden on the country’s energy infrastructure and power grid. With increased functionality and faster processing, power consumption has risen dramatically in today’s systems, resulting in significant energy losses due to wasteful system architectures, inefficient power supplies, lossy components, power hungry cooling, and other similar factors.

To address these issues, regulatory agencies like the Environmental Protection Agency (EPA), industry associations such as Green Grid, and individual consultants and vendors are all promoting their respective best practices for enhancing data center energy efficiency to save power (which ultimately translates into big dollar savings). While there are several proposals being put forth to improve overall data center efficiency and drastically cut power consumption, high-voltage DC power distribution is one that is gaining support from several agencies, including the EPA, Green Grid, the Electric Power Research Institute (EPRI), and the EMerge Alliance.

Toward that goal, researchers at Lawrence Berkeley National Laboratory, the Intel Labs, and some university research centers are demonstrating the energy efficiency benefits of using high-voltage DC power in data centers and telecom systems. Supporting this move are power supply vendors including Delta Electronics, Emerson Network Power, and Vicor Corp., among others delivering practical DC power solutions.

Benefits of DC power distribution

Typically, a data center is supplied power from the grid as AC power, which is distributed throughout the center’s infrastructure. However, most of the electrical equipment, such as servers, solid-state disks for storage, and other IT gear within the infrastructure, (as well as the batteries storing backup power in the UPS system), require DC power. As a result, the AC power must go through multiple stages of power conversion, resulting in power losses and wasted energy. To eliminate these unnecessary conversion steps and, thereby, substantially reduce power wastage, supporters have proposed the use of high-voltage DC power distribution for these systems.

Several studies are being cited in support of the high-voltage DC distribution approach.¹ For instance, a study conducted by Lawrence Berkeley National Labs in 2008 compared the use of 380 V_DC power distribution for a datacom facility to a traditional 480 V_AC power distribution system. The results showed that the facility using DC power eliminates multiple conversion stages to achieve a 7 percent reduction in energy consumption compared to a typical facility with AC power distribution.

Similarly, in a white paper entitled “High-voltage DC distribution is key to increased system efficiency and renewable-energy opportunities,”² Vicor shows that high-voltage DC power distribution (380 V nominal/400 V peak) can substantially reduce energy consumption in data centers and telecom systems as compared to AC distribution. Besides improving energy efficiency, there are several other benefits highlighted in this paper. These include no source synchronization, no phase balancing or harmonic issues, longer battery backup without system derating, a smaller footprint, and a lower total cost of ownership.

Figure 1: In this high-voltage DC distribution approach, the AC input is rectified into a 380 V_DC (nominal) output with backup battery also operating at that high voltage.

In this DC approach (Figure 1), the line AC is first rectified to 380 V_DC (nominal) output with the backup battery also operating at that high voltage. In a typical distributed power architecture, this high DC voltage is stepped down to an intermediate bus voltage using bus converter modules, and is then further lowered to the load voltage using local DC/DC converters. In reality, most circuit functions and devices on the system board operate from DC voltages below 12 V, and even down to <1 V for some processor loads. The challenge for any power supply manufacturer is to deliver bus converter modules and local DC/DC converters along with their high currents efficiently and reliably.

Tangible solutions

To support the high-voltage DC distribution topology, Vicor is offering a variety of isolated bus converter modules labeled BCM, as well as nonisolated DC/DC converters to drive a variety of point-of-load (POL) devices including the latest generation of microprocessors. Because 48 V_DC is a standard bus voltage in many telecom systems used in data centers, members of Vicor’s BCM module series can convert 380 V_DC input to 48 V_DC output with efficiency of over 96 percent, and power density of 70 W/cm³ at power levels of up to 330 W. A good example is BCM384T480T325A00, which incorporates ZVS/ZCS-based sine amplitude converter (SAC) topology to realize high efficiency with high power density.

In systems where an intermediate bus voltage of 12 V_DC or 9 V_DC is required to further drop the 48 V bus voltage, Vicor’s IBC series provides the requisite step-down with peak efficiency close to 98 percent from an eighth-brick footprint and up to 300 W of output power. For instance, Vicor’s IB050E120T32N1-00 is an IBC module that is rated to provide 12 V_DC output from a 48 V_DC input with the ability to handle an input voltage range of 38 to 60 V_DC. It provides an input to output isolation of 2,250 V_DC.

Similarly, for nonisolated POL solutions to power loads like microprocessors, FPGAs, and memory modules, Vicor has readied zero-voltage switching (ZVS) buck-boost regulators in miniature packages with peak efficiency of 97 percent.

Together, as described in the white paper, the BCM and buck-boost regulator provide an equalizer (adapter) function that can operate over the full range of input voltages as defined by ETSI (Figure 2). Consequently, when the input is normal (380 V), the BCM bus converter drops the line voltage down to 48 V with the equalizer operating in a power-through mode (by-passed buck-boost equalizer), thereby maintaining very-high system efficiency. However, when the line DC voltage drops down to 260 V, the buck-boost converter kicks in and maintains the fixed 480 V_DC rail. In either case, Vicor indicates that the architecture maintains high efficiency and allows for seamless, dynamic use of multiple sources such as a rectified DC line, battery, and renewables, as they become available.

Figure 2: Vicor’s bus converter BCM and buck-boost regulator jointly provide an adapter that can operate over the full-range of input voltages as defined by ETSI.

Separately, Vicor’s PI33XX-X0 series of nonisolated ZVS buck regulators offer the ability to step down from a higher bus voltage such as 36 or 24 V_DC to low voltages to directly drive loads on system boards. The manufacturer also offers an isolated PI31xx family to convert 48 V input down to 3.3 V or higher to drive leading-edge IC loads. For example, PI3101-00-HVIZ can deliver 3.3 V_DC output at up to 18 A. Housed in a PSiP package, these modules integrate controller, power switches, planar magnetics, and support components within a single high-density surface-mount package.

In partnership with Emerson Network Power, Vicor has demonstrated a complete 400 V_DC-powered ecosystem at industry shows like INTELEC and Electronica. These demonstrations confirm the feasibility of an efficient high-voltage DC distribution solution using available building blocks and modules (Figure 3). According to Vicor, the solution features high end-to-end efficiency, with no penalty in supporting the ETSI EN 300 132-3-1 voltage range of 260 V to 400 V_DC, while resulting in significant savings in site wiring costs.

Figure 3: A complete 380 to 400 V_DC distribution eco-system based on commercially-available power conversion modules, including components like connectors, fuses, and distribution cabling.

With this demonstration, Vicor believes that it is now practical to use much higher DC voltage for distribution to improve the efficiency of converting and managing power in data centers and telecom systems all the way from DC distribution to the point-of-load.

For more information on the products discussed in this article, use the links provided to access product pages on the Digi-Key website.

References

1. “Is DC Power The Optimal Route For Data Centers To Improve Energy Efficiency?” Ashok Bindra, August 2011.
2. White paper, “High-voltage DC distribution is key to increased system efficiency and renewable-energy opportunities” Stephen Oliver, Vice President, VI Chip Product Line, Vicor Corp.