LAKE WALES, Fla. — In 2010, the U.S. Department of Energy (DoE) set a goal for electric vehicle inverters to be boosted from 4.1 kW/L to 13.4 kW/L by 2020. Now, a 12.1-kW/L inverter has cleared the way to meeting or beating that goal. By using wide-bandgap materials — namely silicon carbide (SiC) — North Carolina State University (NC State) achieved the more-than-tripled performance and has a prototype to prove it (see photo) at the IEEE Energy Conversion Congress and Exposition (Sept. 18–22, 2016, Milwaukee).
"Wide-bandgap power switches offer higher temperature, higher frequency and higher voltage operation capability with lower losses compared to the currently used silicon-based power switches," professor Iqbal Husain at NC State told EE Times.
In addition to approaching the DoE mandate, NC State's wide-bandgap silicon-carbide inverter can also be packaged in a significantly smaller, lighter module, which it claims will increase the fuel efficiency and, thus, the range of both hybrid and all-electric vehicles.
The North Carolina State University inverter for electric automobiles uses wide-bandgap silicon carbide (SiC) semiconductor components to increase efficiency and shrink size to meet 2020 mandaters. Photo courtesy of Iqbal Husain.
(Source: North Carolina State University)
"Efficiency, size and weight reduction are the most important aspects of our inverter,” said Husain. “This was built with all commercial off-the-shelf available components. We can reach the DoE target with some development at the component level, which we can do or the industry is expected to deliver in the near future."
Conventional inverters rely on the narrower bandgap of traditional silicon semiconductors, but the researchers at NC State's Future Renewable Electric Energy Distribution and Management (FREEDM) systems center claim that their wide-bandgap silicon-carbide inverters attained 99 percent efficiency — two percent higher than conventional converters today. They also used off-the-shelf components, giving hope of even better results from highly optimized components made especially for inverters.
In fact, the FREEDM lab is already hard at work manufacturing ultra-high-density silicon-carbide components that they hope will allow them to reach the DoE's goal long before 2020. The researchers are also working on stripping out the liquid cooling systems required by today's inverters because the wide-bandgap materials produce much less heat than narrow-bandgap materials. The current prototype is a 55-kW model, but air-cooled versions will probably be possible for smaller motors of about 35 kW — the kind used for motorcycles and small hybrid automobiles. The lab is also working on scaling up its off-the-shelf component model to a 100-kW version usable in full-sized all-electric vehicles.
"Thermal management is a key aspect of the design," said Husain. "The heat has to be moved out so that the power switches and other components can operate more efficiently and also don't fail due to thermal problems."
Get all of the details in two papers being presented this week at ECCE:
A paper on the new inverter, "Design Methodology for a Planarized High Power Density EV/HEV Traction Drive using SiC Power Modules", describes the overall design philosophy of the inverter, and "Development of an Ultra-high Density Power Chip on Bus Module" gives a system-level explanation of how a planar architecture high-power-density inverter was built from off-the-shelf SiC power modules.
Funding was provided by the PowerAmerica Institute at NC State, the DOE’s Office of Energy Efficiency and Renewable Energy and the National Science Foundation.
Other contributors besides Iqbal Husain include Dhrubo Rahman, Adam Morgan, Yang Xu, Rui Gao, Wensong Yu, Douglas Hopkins, Yang Xu, Harvey West and Wensong Yu.
— R. Colin Johnson, Advanced Technology Editor, EE Times