NCSU’s FREEDM Systems Center develops low-cost SiC high-voltage switch

Researchers at North Carolina State University (NCSU) have created a high-voltage and high-frequency silicon carbide (SiC) power switch that could cost much less than similarly rated SiC power switches, it is reckoned. The findings could lead to early applications in the power industry, especially in power converters such as medium-voltage drives, solid-state transformers, and high-voltage transmissions and circuit breakers.

Wide-bandgap semiconductors such as SiC show potential for use in medium- and high-voltage power devices because of their capability to work more efficiently at higher voltages. Currently though, their high cost impedes their widespread adoption over the prevailing workhorse and industry standard – silicon-based insulated-gate bipolar transistors (IGBT) – which generally work well but incur large energy losses when they are turned on and off.

However, the new SiC power switch could cost about half the estimated cost of conventional high-voltage SiC solutions, say Alex Huang and Xiaoqing Song, researchers at NCSU’s FREEDM Systems Center, a US National Science Foundation (NSF)-funded engineering research center (ERC). Besides the lower cost, the high-power switch maintains the SiC device’s high-efficiency and high-switching-speed characteristics, i.e. it doesn’t lose as much energy when it is turned on or off.

The FREEDM Super-Cascode power switch combines 12 smaller SiC power devices in series to reach a power rating of 15kV and 40A. It requires only one gate signal to turn it on and off, making it simple to implement and less complicated than IGBT series-connection-based solutions. The power switch is also able to operate over a wide range of temperatures and frequencies due to its proficiency in heat dissipation (a critical factor in power devices).

“Today, there is no high-voltage SiC device commercially available at voltage higher than 1.7kV,” says Huang, Progress Energy Distinguished Professor and founding director of the FREEDM Systems Center. “The FREEDM Super-Cascode solution paves the way for power switches to be developed in large quantities with breakdown voltages from 2.4kV to 15kV.”

At the IEEE Energy Conversion Congress & Exposition (ECCE 2016) in Milwaukee (18-22 September), Xiaoqing Song (a Ph.D. candidate at the FREEDM Systems Center under Huang’s supervision) presented the paper ’15kV/40A FREEDM Super-Cascode: A Cost Effective SiC High Voltage and High Frequency Power Switch’.