Cutting the cord has been a longtime dream for EV charging, but it’s been stymied in part by anemic charging rates. Now, Oak Ridge National Laboratory (ORNL) has succeeded in juicing a Porsche Taycan EV sedan at a record 270 kilowatts, with nary a cord in sight. This comes just three months after Oak Ridge announced a then-record 100-kW wireless charge for a Hyundai Kona crossover SUV.
That zippy 270-kW flow is on par with some of the fastest public DC chargers around. And even on the mightiest DC chargers rated for 350 kW, cars like the Taycan and Hyundai Ioniq 5 can still only charge at levels up to around 230 to 250 kilowatts. That charging level can replenish compatible EVs from 10 percent to 80 percent in less than 20 minutes. According to ORNL, its wireless system could add a 50 percent gain in battery charge in about 10 minutes, appreciably faster than previous wireless systems.
The Oak Ridge system pairs a magnetic resonance transmitter pad with a receiver mounted to the underside of the car. The system’s secret sauce is its polyphase windings—lightweight electromagnetic coils arranged over a coil to generate a rotating magnetic field that eliminates current ripples and field cancellation.
The EV charging system’s lightweight polyphase coupling coils create a rotating magnetic field for continuous power transfer.ORNL/U.S. Department of Energy
“You have constant power transfer, rather than pulsations across the air gap, so there’s a substantial improvement in space-time utilization of the magnetic field,” says Omer Onar, leader of ORNL’s Vehicle Power Electronics Research Group. The resulting system, Onar says, can deliver eight to 10 times as much power density as comparable single-phase wireless chargers, and at more than 95 percent efficiency.
The system is compact on both the transmitting and receiving ends. Onar says the powerful 270-kilowatt receiver fits into the space that Porsche carved out for a potential 11-kilowatt wireless charger on future versions of the Taycan. The electromagnetic coils in the receiver are less than 50 centimeters in diameter. ORNL said its system is the world’s lightest wireless charging unit on a per-kilowatt basis—at 7.5 kilowatts per kilogram, versus 1.9 kW/kg for the Brusa company’s wireless system, which delivers just 22 kW of power overall.
Onar ticked off several potential advantages over wired systems. There’s no need to wrestle with bulky charging cables and plugs, a particular burden for elderly and handicapped users. And there are no cables that could be vandalized or stolen for their copper wiring, as has happened in a recent wave of thefts that’s left some charging stations inoperable.
What’s more, the wireless charging system should be easier to maintain. The liquid-cooled DC cables used at many charging stations require regular maintenance, to replace components such as plug connectors—a notorious failure point on non-Tesla combined-charging system units—as well as pumps, fans, and heat exchangers. And those DC cables often sharply dial back power when they reach a maximum temperature, which tends to happen after repeated back-to-back fill-ups. Onar says that other national labs tested a popular 350-kW charger and found its cables could not exceed 50 °C before cutting charge power.
Allowing drivers to simply park atop an underground charging pad could solve another wired frustration: cables that are too short to reach EVs that have their charge ports in unconventional locations, or cables that won’t reach because the charger stall is poorly positioned. And unlike many older wireless systems, which required a near-perfect parking job, the Oak Ridge system doesn’t even require the car to be perfectly aligned over the underground pad. With the ORNL system, the car can be misaligned by more than 12 centimeters and still receive an efficient charge; ultimately, the system might use your car’s cameras and onboard guidance to line things up.
Onar says wireless systems would be ideal for coming generations of robotaxis that have no human driver aboard. Small fleets of such robotaxis are already operating in China and some parts of the United States and Europe.
“The cars may self-drive and self-park, but you still need someone to plug them in,” Onar says.
Even today, Onar says, many drivers for UPS or other delivery services are forbidden by work rules to refuel vehicles themselves. Wireless refueling could be largely automated; you’d just park the truck and walk away.
The prototype 270-kilowatt charger can work with cars and trucks with varying ground clearances. The relatively low-slung Taycan had a 12-centimeter air gap between receiver and transmitter. Onar says that in a joint project with UPS, the system works across gaps up to 28 centimeters, enough for delivery trucks or even semi trailers.
As for safety, ORNL says the system meets all electromagnetic field emission limits, emitting, at 270 kW, a roughly 19-microtesla electromagnetic field, and that’s without any shielding. A single-phase circular system, Onar says, would likely emit more than 57 µT at similar power levels.
The car-mounted receivers can operate across a full range of power classes, from slower home charging to the most powerful DC units. Onar says early deployments may focus on home charging pads that could deliver 11 to 22 kilowatts. Commercial applications are at least several years away, though, as the technology still needs to move from lab to manufacturing.
ORNL has been working the wireless-charging problem for more than 10 years. The latest Porsche project is the fruit of a collaboration with Volkswagen, Porsche’s parent company, that kicked off in 2021, funded by the U.S. Department of Energy. Hyundai Motor America and Stellantis are among the other automakers sponsoring the Oak Ridge research. The lab sees commercial potential not just in EV charging, but in wireless charging pads for smartphones and other personal electronics, along with industrial equipment such as drones, automated guided vehicles, and other mobile robots.
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