Power> Supplies And Batteries

While walking through the exhibits at a power industry trade show last fall, I was struck by the number of vendors showing off flywheel power systems. These flywheels formed the heart of uninterruptible power supplies (UPSs), which were intended to complement or compete with traditional battery-based UPSs. I counted at least three booths exhibiting flywheel power systems in the hall, which surprised me. I couldn't ever recall seeing so many at one power electronics trade show.

Then I noticed an exhibit on a fuel-cell-backed UPS from a major UPS vendor. That triggered memories of another fuel-cell UPS I had seen at last year's show. Flywheels and fuel cells aren't exactly new, but the effect of seeing these various flywheel and fuel-cell displays made a definite impression. There really are alternatives to batteries and generators when it comes to power backup. Within the next few years, it's very possible that these alternative energy storage elements will prove themselves in the real world. As David Townley of Pentadyne notes in his commentary below, there is already a long-term economic incentive to replace lead-acid batteries with flywheel power systems.

Flywheel and fuel-cell UPSs both have the potential to improve reliability and save space, energy, and cost in power backup systems. Those same potential benefits are being pursued by power-supply developers. Each generation of supplies seeks greater performance, smaller size, and lower cost.

In its recently released technology roadmap, the Power Sources Manufacturers Association (PSMA) has projected just how rapidly the industry is moving toward those goals. Some of the numbers that benchmark this progress are shown in the Top Ten, but these numbers just scratch the surface. The PSMA's roadmap provides in-depth detail on how application requirements for power are changing and how power-conversion technologies are evolving through both architectural and component developments.

Many of the power-supply developments cited here appear to be more evolutionary than revolutionary. But in the power-supply field, incremental advances have a way of turning into big gains in the long run.

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• AC-DC POWER SUPPLIES in the 1000-W range with 12- to 48-V outputs are expected to see continued improvements in power density and efficiency according to the Power Sources Manufacturers Association's (PSMA) five-year forecast. Power density now in the 3- to 10-W/in.³ range should rise to the 10- to 25-W/in.³ range in 2008. Efficiency for these supplies should rise from the 80% to 85% range to an 85% to 92% range.
• COST REDUCTIONS FOR 1000-W power supplies are also projected by the PSMA. Power supplies are now priced at about 10 to 20 cents per watt. In 2008, those values could fall to 8 to 14 cents per watt.
• BOTH FUEL CELLS AND FLYWHEELS will begin to make inroads in uninterruptible-power-supply (UPS) applications. Fuel cells will offer extended-duration backup to replace battery banks and possibly some diesel generators. For instance, MGE's Evolution is a 3-kVA UPS powered by Ballard's Nexa RM series of proton-exchange-membrane (PEM) fuel-cell modules. Powered by canisters of hydrogen gas, the UPS will provide run times ranging from four to 24 hours, depending on the amount of fuel storage. MGE, which began field trials of the Evolution UPS last year, plans to put this product into commercial production this year. Although the technology will initially offer 1 to 3 kVA of rack-mounted backup power, the fuel-cell technology is scalable, allowing the company to provide power levels up to 30 kVA in the future.
• FLYWHEEL-BASED UPSs WILL complement or replace battery-backed UPSs as a way to provide short-term backup or "ride-through." Because flywheels can offer greater reliability than batteries, they promise to lower system maintenance costs and reduce space requirements versus batteries.
• SWITCHING POWER SUPPLIES will continue to supplant low-cost linears in even the lowest-power applications. The trend will be aided by regulatory standards that call for reduced standby power consumption and by offline switching controller ICs, which lower power-supply design costs. Switching supplies based on the offline controller ICs promise to replace even some of the non-isolated, passives-based, low-current supplies now employed in industrial applications and "white goods" appliances.
• HOW DO COMPANIES like Dell, Hewlett-Packard, and Cisco qualify as power supplies and power-supply vendors? Attend a seminar on this topic at the Applied Power Electronics Conference and Exposition (APEC), Feb. 22-26, Anaheim, Calif. The conference will present nearly 300 technical papers on a wide range of power-conversion topics.
• THE APEC 2004 PLENARY SESSION will provide a look at some of the hot-button issues in power electronics. Speakers will discuss the PSMA's five-year technology roadmap, developments in digital control, a leading OEM's call to action for the industry to meet the increasingly difficult requirements of electronic equipment, a forecast for the power electronics business, and other topics.
• SAFER BATTERIES AND MORE POWER-DENSE RECTIFIERS could drastically alter the way telecom central offices are powered in the near future. According to Valere Power, the new batteries and rectifiers should make it possible to move from centralized to distributed power architectures. Co-locating power and communications equipment will greatly reduce power distribution infrastructure and cabling. The resulting cuts in material and labor costs should more than offset the added cost of the new batteries and rectifiers.
• LI-ION BATTERIES WILL CONTINUE to be the rechargeable battery of choice in high-volume portable applications, such as cell phones. These batteries will keep gaining market share over NiCd and NiMH batteries. Unfortunately, no dramatic increases in this chemistry's battery capacity appear to be on the horizon.
• MORE SOPHISTICATED POWER AND BATTERY-MANAGEMENT techniques will help offset the lack of progress in Li-ion battery technology. More accurate fuel gauging for single-cell Li-ion applications will increase the effective battery capacity, while more versatile charger ICs accept power from additional sources like a USB port or even a powered-Ethernet port.