Wireless tech powers EVs without charging stations — study

Source: By David Iaconangelo, E&E News reporter • Posted: Wednesday, May 13, 2020

A wireless charger developed by Stanford University engineers could one day refuel an electric car while it’s still on the road, allowing drivers to skip the slow charging stations that have discouraged EV adoption.

The Stanford team’s system, described in a study published in Nature Electronics last week, uses the same basic design as most wireless chargers. Two magnetic coils face each other, with one acting as the “source” coil that transits electricity toward the “receiver” coil.

The same research team previously had determined how to charge an object while it moved through the magnetic field between the coils. But the team’s latest research advances the technology by allowing the coils to provide a consistent stream of power while losing almost none of it in the process.

“The problem with it previously was that the total efficiency wasn’t that good. We spent a lot of time on improving that,” said Sid Assawaworrarit, co-author of the study and a doctoral candidate in electrical engineering at Stanford.

The system hasn’t been tested beyond the lab, where it transmitted a small fraction of the electricity needed to power a car over just a few feet of space.

But no “serious roadblock” to scaling up the system exists, according to the researchers.

“In terms of the fundamental capabilities, I don’t think there’s anything that would prevent this from realizing the dynamic charging that this is all about,” said Assawaworrarit.

The strength of the charge being sent into the car’s battery “can be scaled up by cranking up the power supply on the power source side and is independent of the car speed,” he said.

If very large source coils were constructed underneath roadways, Assawaworrarit reasoned, they could send a powerful charge toward a receiver coil carried by an electric car and boost its battery’s range. Most electric vehicles don’t compete with gas cars in terms of range from one fueling, creating one of the most important disincentives to electric car adoption.

A handful of public transit agencies in the United States, like those in Long Beach, Calif., and Chattanooga, Tenn., have already experimented with “inductive” or wireless recharging for electric buses, since they travel the same route on a fixed schedule. In those instances, buses pull up to a charging pad at a bus stop and get a quick jolt of extra power, without posing safety issues to pedestrians.

For bus fleet managers, systems of that kind don’t always provide power quickly enough to justify the expense, however. On-the-go wireless models would likely have to contend with that, too.

Still, there’s a financial incentive in favor of the technology: Dishing out enough power while the bus is in service means it could use a smaller battery, which would slash the single biggest source of cost for any electric vehicle.

“If you can charge on the go, instead of having a hundred-kilowatt battery, you can have one with tens of kilowatts,” said Assawaworrarit.

The team is working now on improving the system’s ability to send an equal, steady charge to multiple objects passing through the magnetic field at the same time.

“We’re looking into more of a use-case scenario, like having a big source coil powering a number of devices,” said Assawaworrarit. “Instead of powering one thing, you would power three or four.”