EPRI reaches milestone in advanced power electronics with silicon carbide switch

PALO ALTO, Calif., Dec. 16, 2004 — Researchers at the Electric Power Research Institute (EPRI) have announced the development of high power switches made from silicon carbide (SiC) crystals. The one square-centimeter devices represent a milestone in power and size that could significantly improve the performance of advanced power electronics used to control the bulk flow of electricity.

“The silicon carbide switch is a critical enabling technology for the future of the electricity system that we have outlined in the EPRI Electricity Technology Roadmap,” said Clark Gellings, EPRI’s VP for Innovation. “As power electronics are incorporated into the power delivery system, utilities will be able to exert better control over power flow and protect their customers from outages and other power quality problems.”

The new technology has an electronic structure that allows it to support ten times higher voltage gradients and operate at higher temperatures than silicon. It also has a thermal conductivity three times higher than silicon – slightly better than copper. Because of these properties, SiC has the potential to provide devices with ten times the voltage limit of silicon and with two to three times the current density. The SiC switch, manufactured by Cree, Inc., blocks 1750 V and conducts 250 Amps, and operates up to 250°C junction temperature.

Commercialization of SiC technology was inhibited for many years by the quality of available SiC crystals, says Dr. John Palmour, Cree’s Executive Vice President for Advanced Devices. However, recent R&D funding from the U.S. government has enabled researchers to increase the diameter of production wafers to 75 mm. (3 in.) and to drastically reduce the number of defects in the crystal. EPRI subsequently funded a demonstration project employing the wafers in prototype power electronics devices. The reduction in defect density allows the devices to be larger than ever before, which in turn makes the devices more commercially viable.

This important development in SiC wafer production has implications for the use of power electronics as it will allow devices to be smaller, less costly, and have fewer parts than their silicon counterparts. Initially, this type of device will be used in motor drives for industrial plants and eventually in the thyristors of flexible AC transmission system (FACTS) devices that provide control over the flow of power through high-voltage transmission lines.

Over many years, funding for SiC research has been provided through the Defense Advanced Research Projects Agency (DARPA) of the Department of Defense (DoD) and the DoD’s Title III program. The U.S. military anticipates that the compaction and ruggedness of the SiC devices will enable electric cannons and solid state power distribution systems on tanks and ships.

“Scientists have long recognized that silicon carbide has the potential to be much more efficient than silicon for power devices, but they were skeptical about commercializing the compound any time in the near future. This milestone demonstrates that silicon carbide power devices are just around the corner,” said Ben Damsky, EPRI’s manager for power electric systems.

About EPRI [ www.epri.com ]

EPRI, with major locations in Palo Alto, Calif., and Charlotte, N.C., was established in 1973 as an independent, non-profit center for public interest energy and environmental research. EPRI’s collaborative science and technology development program now spans nearly every area of power generation, delivery and use. EPRI’s members represent over 90% of the electricity generated in the United States. International participation represents over 10% of EPRI’s total R&D program, with 62 members and more than 130 funders.

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