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Low-cost HV SiC switches could enhance drives

07 October, 2016

Researchers in the US have created a high-voltage, high-frequency silicon carbide (SiC) power switch that could cost about half as much as conventional HV SiC power switches. They say that their device could help to cuts the costs and boost the performance of applications such as medium-voltage drives, solid-state transformers, HV transmission systems and circuit-breakers.

The new devices could also help to extend the range and performance of electric and hybrid vehicles by allowing the use of smaller, lighter inverters that do not need liquid cooling.

Wide-bandgap semiconductors, such as SiC, show tremendous potential for use as medium- and high-voltage power devices because they work more efficiently at higher voltages. To date, however, their high costs have limited their widespread adoption compared to silicon-based IGBTs (insulated-gate bipolar transistors), which work well but incur large energy losses when they are turned on and off.

The new SiC power switch – being developed by researchers at the North Carolina State University’s FREEDM (Future Renewable Electric Energy Distribution and Management) Systems Center – could cost about half as much as existing high-voltage SiC devices. The new device retains the high efficiency and high switching speeds of SiC devices, without suffering the energy losses of Si devices when they are switched on or off.

The switch, called the FREEDM Super-Cascode, combines 12 small (1.2kV), off-the-shelf SiC power devices in series to reach a power rating of 15kV and 40A. It needs only one gate signal to turn it on and off, making it simple to implement and less complicated than IGBT systems based on series connections. The new switch is also able to operate over a wide range of temperatures and frequencies due to its effective heat dissipation.

The low-cost, high-voltage silicon carbide switch could lead to cheaper, more efficient SiC-based converters

“Today, there is no high-voltage SiC device commercially available at voltage higher than 1.7kV,” explains Alex Huang, Progress Energy Distinguished Professor and the 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 2.4–15kV.”

The US researchers says that inverters based on their switches could operate with efficiencies as high as 99% – 2% better than the best silicon-based inverters. And their low heat dissipation means that the inverters could be air-cooled rather than needing bulky and costly liquid cooling. This could be a particular advantage in electric vehicle applications.

The new device will cost only one third to half as much as existing high-voltage SiC Mosfets, and will facilitate early applications of SiC in high-voltage and high-frequency power converters.




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