Using 400 Vdc for Efficient Distribution of Data Centre Power

November 5, 2012
    Power efficiency in supercomputersWithin telecommunications and data centres, continuing growth in processing equipment’s power demand is imposing evolutionary change on the power architecture that feeds it. As AC distribution utilising AC UPSs becomes too expensive and complicated, the natural response is to distribute at higher DC voltages to reduce I²R losses across the supply infrastructure. So how has this infrastructure evolved, and which building blocks are now available for integration into an efficient power solution for today’s data and telecommunications centres?

    Across the telecommunications industry, DC power distribution has been the norm for decades. Schemes using bulk power distribution were among the earliest installed. More recently, some users migrated to distributed 48 Vdc site architectures, which feature modular rectifiers arranged in-row with the powered loads. Higher copper content interconnections are used to contain distribution losses. The modular configuration also allows for very high availability, by using ‘N+1’ identical modules. N represents the number of modules needed to fully supply the load, so an ‘N+1’ configuration can do so even if one module fails.

    Both approaches – bulk and 48 Vdc distributed – can be replaced by 400 Vdc distribution to achieve lower losses and higher efficiency. Higher voltage DC distribution also provides many advantages over another popular approach: AC distribution employing AC UPSs. Higher efficiency comes from fewer conversion stages in the overall system, and battery backup lasts longer without system derating. Power source and distribution are inherently  not affected by harmonic losses  nor need complicated load balancing mechanisms between phases. The systems allow smaller footprints, simplified distribution switchgear and easier maintenance.   A single global voltage of 400 Vdc becomes the universal interface between sources (including renewables) and equipment.

    There are practical and legacy considerations associated with moving to 400 Vdc; much existing equipment is designed for 48 Vdc power, so a simple and effective interface is needed between the two levels. At the same time, equipment manufacturers should design and introduce new hardware that can directly accept the higher DC voltage. Systems comprising state-of-the-art computing, routing and optical hub equipment can become simpler, more efficient and more cost-effective to operate.

    Within these new distribution systems, utility AC power is converted by a rectifier bank to stable, well-regulated 400 Vdc for distribution to the critical loads. To fully benefit from higher DC voltage distribution, it is necessary to optimise the powered equipment’s conversion topologies, including both ‘front end’ and internal conversion stages on motherboards.

    Various ‘building blocks’ can be used to implement these topologies, with each being optimised for their particular role. Sine Amplitude Converters (SACs) act as ‘DC transformers’, offering peak efficiencies above 97% and power densities to 120 W/cm³ (2000 W/inch³).  SACs are ideal for efficiently translating voltage levels both for power distribution and at point of load. In practical implementations, two main components exploit this topology: the Intermediate Bus Converter (IBC) and the point-of-load Current Multiplier (CM). Zero Voltage Switching Buck Boost Converter topology (ZVS-BBS) offers maximised efficiency and power density at small input-to-output regulation ratios. This topology is implemented in two components: The Equalizer, used for holding up voltages during power interruptions, and the point-of-load Regulators.

    These components can be designed into optimised architectures against a reference framework comprising several key points. Power systems should not trade-off conversion efficiency during nominal conditions to sustain rare, abnormal events. Distribution losses should be minimised by adopting higher voltages across the entire system to the point of load, and power system designs should be flexible to accommodate the different device types found in data centre servers. Most step-down should be obtained from SAC devices, while regulator range should be minimised whenever possible, maintaining higher efficiency.

    We are running a series of online webinars in November, including:

    20-20-20 Energy Strategy: Using 400VDC Distribution to Save Energy and Make Money

    Session 1: Tuesday, 13 November (14:30 London, 15:30 Munich, 06:30 San Francisco, 09:30 Boston)
    Session 2: Wednesday, 14 November (14:30 London, 15:30 Munich, 06:30 San Francisco, 09:30 Boston)

    [These sessions are now complete.  However, the the rebroadcast version is available to view, in English and German.]

    Alternatively, if you are visiting electronica (13-16 November) you can attend the seminar itself. Visit Hall A6, Stand 560.

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