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From: slacker71111/28/2018 7:11:21 AM
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Oak Ridge Inches Closer to 15-?Minute Wireless EV Charging
But the team must further scale their 120-kilowatt wireless charging system for electric vehicles in order to meet the U.S. Department of Energy’s goal
By Mark Anderson


To beam wireless power from a floor unit to a power receiver unit in an EV, separated by some six inches of open air, means rapidly oscillating the electric and magnetic fields in the coil, inducing similar behavior in the receiving coil in the EV. Practically speaking, Ozpineci says, that means pumping out 120 kilowatts through oscillating currents at some 22,000 cycles per second (i.e., 22 kilohertz).

“The problem is typically we have silicon devices, and when we go to higher power levels, you cannot run them at higher switching frequencies,” he says. “At 10 kW, you can switch at 20 kHz. But when you go up to 100 kW and beyond, you have to reduce your switching frequency—because of thermal issues, because of the device response, because of a number of things.”

But transferring higher power levels at high efficiency demands higher switching frequencies. So this effectively means both swapping out silicon for more robust (and more expensive) silicon carbide and strengthening the coils on both sending and receiving ends of the power exchange.

Tesla’s Model 3 also uses silicon carbide electronics, Ozpineci says. So the Oak Ridge technology’s reliance on the material is not unprecedented in EV systems. On the other hand, they admit their 100-pound (45-kilogram) coil needs some refining and optimizing before it could ever be scaled out into a production-quality design.

Then, they must produce three times more power from their design to reach the Energy Department’s 350- to 400-kW target. Ozpineci says it’s a work in progress, but he suspects there will have to be multiple power modules in any 350-kW or more wireless supercharger.

“We’re able to use single power modules,” he says of the current 120-kW unit. “We’re at the limit or almost at the limit of these power modules. When you go to anything beyond that, we’ll have to either parallel these modules, or we have to have two inverters in parallel. And when you do that, you have a lot more challenges of running these things in sync.”
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