NC State team develops new SiC inverter; 12.1 kW/L & greater efficiency in a smaller, lighter package
Researchers at the Future Renewable Electric Energy Distribution and Management (FREEDM) Systems Center at North Carolina State University have developed an inverter for hybrid and electric vehicles using off-the-shelf components made of the wide-bandgap semiconductor material silicon carbide (SiC).
The new SiC-based inverter has a power density of 12.1 kW/L—close to the US Department of Energy’s target of 13.4 kW/L by 2020. By way of comparison, a 2010 electric vehicle could achieve only 4.1 kW/L. Further, says Iqbal Husain, ABB Distinguished Professor of Electrical and Computer Engineering at NC State and director of the FREEDM Center, the silicon carbide prototype inverter can transfer 99% of energy to the motor—about two percent higher than the best silicon-based inverters under normal conditions.
The design of the new power component is also more effective at dissipating heat than previous versions. This could allow the creation of air-cooled inverters, eliminating the need for bulky (and heavy) liquid cooling systems.
Bi-directional interleaved DC-DC boost structure and a three-phase voltage source inverter (VSI) were utilized with the primary focus on the size, weight and loss reduction of passive components. A stacked layer approach was used for a unique PCB-based busbar, ultra-low profile gate driver, and controller board.
The Power Chip on Bus (PCoB) power module approach that reduces parasitic inductance through an integrated power interconnect structure. The PCoB maximizes thermal performance by direct attaching power chips to the busbar, integrating the heatsink and busbar as one, and uses a dielectric fluid, such as air, for electrical isolation.
The team is presenting two papers on the inverter at IEEE Energy Conversion Congress and Exposition (ECCE) next week in Milwaukee.
We predict that we’ll be able to make an air-cooled inverter up to 35 kW using the new module, for use in motorcycles, hybrid vehicles and scooters. And it will boost energy density even when used with liquid cooling systems in more powerful vehicles.—Iqbal Husain
The current SiC inverter prototype was designed to go up to 55 kW—a level of power seen in a hybrid vehicle. The researchers are now in the process of scaling it up to 100 kW—akin to what would be needed in a fully electric vehicle—using off-the-shelf components.
The researchers are also in the process of developing inverters that make use of the new, ultra-high density SiC power component that they developed on-site.
Dhrubo Rahman, Adam J. Morgan, Yang Xu, Rui Gao, Wensong Yu, Douglas C. Hopkins and Iqbal Husain (2016) “Design Methodology for a Planarized High Power Density EV/HEV Traction Drive using SiC Power Modules” 2016 IEEE Energy Conversion Congress and Exposition
Yang Xu, Iqbal Husain, Harvey West, Wensong Yu and Douglas Hopkins (2016) “Development of an Ultra-high Density Power Chip on Bus (PCoB) Module” 2016 IEEE Energy Conversion Congress and Exposition