It’s often assumed that while energy-efficient “green” supplies will shrink operating costs over the long haul, the initial outlay will be rather steep. Therefore, the return-on-investment (ROI) decision isn’t so clear-cut, even though these supplies ultimately reduce the required line power and subsequent thermal-load dissipation.
However, that scenario may not necessarily be the case. By using the right power-transformation and distribution approach, it’s possible to increase operating efficiency as well as reduce upfront investment—like many network providers, data-center operators, and even suppliers of adapter subsystems have already discovered.
The key is to stay with higher voltages as much as possible, isolate and transform the power where needed, and regulate it only when it’s absolutely necessary. To that end, high-voltage dc (HVDC) distribution and downconversion will minimize the total cost of ownership (TCO) from ac to the point of load. (Historical note: This revisits the 19th century battle of Edison (dc) versus Tesla (ac), although obviously on different terms and with very different components.)
Work by telecom providers such as France Telecom (Orange) and China Mobile put “HVDC plus HV back-up” energy saving estimates at 8% to 10% versus traditional “ac plus UPS” systems. The questions of power conversion and applicability to legacy 48-V systems also have been resolved.
The required conversions and transformations can be accomplished with building blocks such as Vicor’s sine amplitude converter. It may be used as a high-voltage intermediate bus converter or point-of-load current multiplier, or as a zero-voltage switching (ZVS) buck-boost converter for regulation or equalization (which regulates only when voltage falls below normal operating range of 365 V ± 15 V).
This isn’t simply a speculative approach. A small-scale demonstration was built using standard, commercially available components, with the functional blocks needed to support representative telecom and datacenter loads beginning with primary-line ac (see the figure). The wall outlet is converted to 400 V dc, which enables it to directly support a HV LED lighting strip. In addition, by using 1:8 and 1:32 intermediate bus converters (IBCs), it provides regulated and unregulated 48 V dc and 12 V dc for other loads and converters.
Another benefit of the HVDC approach is that it more easily integrates with backup battery subsystems and renewable sources, such as solar and wind, for additional reliability. Further, because all of these sources are dc, it avoids any ac synchronization, phase balancing, or harmonic problems.
HVDC became a reality thanks to industry-wide collaboration among disparate groups at various levels. They established standards for HVDC systems for commercial installations (e.g., offices), as well as infrastructure functions (e.g., datacenters).
These standards, for example, define distribution and connectors for use with LED lighting, HVAC units, and fans from high-voltage buses, while also addressing safety issues. They include the European Telecommunications Standards Institute (ETSI) EN 300 132-3-1, corresponding efforts in Japan and North America via the Telecommunication Standardization Sector of the International Telecommunication Union (ITU), the IEEE, the National Electrical Manufacturers Association (NEMA), and the National Fire Protection Association (NFPA), among others.
The Next Step
Making the switch from today’s topology to an HVDC approach can be accomplished with a transitional phase, where that makes technical and economic sense. In such a situation, an ETSI “adapter” can be built from, say, Vicor’s high-voltage BCM bus converter (which maximizes efficiency during normal operating conditions) and the company’s buck-boost PRM regulator (which kicks in only upon failure of the ac line fails and/or the 400-V battery decay). This “adapter” enables efficient connection of existing end equipment (routers, switches, etc.) to the 400-V bus. Subsequent new designs can connect directly to the high-voltage rail.