Hands-free: Wireless charging system advances electric vehicle convenience

Consumer buy-in is key to the future of a decarbonized transportation sector in which electric vehicles largely replace today’s conventionally fueled cars and trucks. Oak Ridge National Laboratory scientists have for several years now steadily advanced a wireless charging technology that can make powering an EV just as easy, or easier, than filling up a car with gas. The researchers are now nearing the completion of a new system to charge EVs while they’re in motion. 

Electrifying transportation is at the top of the list for solutions to decarbonize the American economy. The transportation sector is the largest source of greenhouse gases in the nation, with cars and light trucks alone accounting for 60% of emissions. The Department of Energy has supported a range of research to make EV ownership more convenient and less costly for consumers, including the goal of a 15-minute or less charge time.

With custom magnetic coils, silicon carbide-based power electronics, and novel controls and shielding technology to handle stray emissions, ORNL scientists have proven that their system can wirelessly charge both a light-duty passenger car across a six-inch airgap and a medium-duty delivery truck across an 11-inch airgap at the 20-kilowatt level at greater than 92% power transfer efficiency — on par with a wired system. Power can even flow in both directions, enabling vehicles to serve as energy storage. 

The researchers have successfully demonstrated a 120-kW wireless charging system with 97% efficiency, and are planning to install higher voltage systems, up to 270-kW, on passenger vehicles to meet or exceed the 15-minute charging goal.

The research is supported by the DOE Office of Energy Efficiency and Renewable Energy’s Vehicle Technologies Office. The systems are built and evaluated at the National Transportation Research Center at ORNL, the only DOE-designated user facility focused on performing early-stage research and development in transportation technologies. The medium-duty vehicle wireless charging demonstration was held at the new Grid Research Integration and Deployment Center, or GRID-C, at ORNL, which combines multiple electrification research across the vehicle, buildings, and grid space.

The researchers now have a finish line in sight for a system called dynamic wireless charging in which vehicles are automatically energized while rolling over specially equipped roadways. The researchers will make use of a new, one-of-a-kind test bed at GRID-C to evaluate the dynamic wireless charging system and to support research on how the technology will smoothly integrate into the nation’s power grid.

“Once you get to these higher power levels to enable fast charging, you especially don’t want people handling the heavy cables typically required,” said Burak Ozpineci, who heads ORNL’s Vehicle and Mobility Systems Research Section. “With wireless technology you wouldn’t have to remember to plug in your vehicle at home, and it’s always topped off. You just park it in the garage and it’s done. The same with charging pads at workplaces or at extreme-fast wireless charging stations.”

“Now we want to take it a step further. What if you have an EV and never have to worry about having enough of a charge to go anywhere you like? We can accomplish that with dynamic wireless charging,” Ozpineci said.

With dynamic charging, for instance, some highway lanes or even on- and off-ramps would be embedded with charging pads, and your car is charged as you drive it over the coils. You would exit and enter the highway with the same battery charge.

Dynamic charging can also reduce the grid impact resulting from the peak demand of overnight charging in homes or at charging stations, Ozpineci said. Instead, that demand for EV charging would be level and allow for better grid stability.

ORNL’s dynamic charging goal is for a 200-kW system that can quickly charge vehicles at highway speeds. The economics look good. Installing dynamic charging on heavily traveled roadways means the cost of the system would be spread across many users, bringing the cost of ownership down.

Convenient charging could even encourage the adoption of electrified semi trucks, said Veda Galigekere, who leads the Electric Drives Research Group at ORNL. Once the dynamic system undergoes full evaluation at GRID-C, it will be tested at the American Center for Mobility in Michigan.

The success of ORNL’s wireless charging technology relies heavily on researchers’ broad expertise in power electronics, control systems, electrical engineering and electromagnetics. A key development in the evolution of the ORNL wireless tech was the creation of a polyphase magnetic coil coupling design that allows for much higher power density in smaller coils. The design encompasses a three-phase system that features rotating magnetic fields between layers of coils.

Even at the 300-kW level, the ORNL coil design has a much smaller footprint than currently available wireless charging technology due to that higher surface power density. The ground-based coil is about the size of an extra-large pizza, while the coil on the car is about the size of a small or medium pizza, said Omer Onar, who leads the lab’s Vehicle Power Electronics Research Group.

Another important challenge in the work is resolving the issue of stray electromagnetic emissions around the coils. ORNL is developing advanced shielding technology to control those emissions and the heat they can produce. The solution uses nano-crystalline materials together with aluminum to create a magnetic-metallic hybrid shielding technology that dampens emissions. The technology has been validated up to the 50-kW level already, Onar added.

Automatic charging of vehicles resolves a major stumbling block for consumers who are hesitant to buy an electric vehicle. While consumers are increasingly aware that the newest EVs offer a lot of power, they also worry about whether they can get where they’re going with currently available charging infrastructure.

“If you can charge wirelessly at home, at work, and even when you’re on the way, you never have to think about charging your car and you eliminate range anxiety,” Ozpineci said.

Source: ORNL, Stephanie G Seay

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Published May 20, 2021