Research paves way for wireless charging of electric vehicles

ITHACA, N.Y. – Researchers at Cornell University are pioneering a new way to wirelessly charge electric vehicles, autonomous forklifts and other mobile machines, while they remain in motion.

Imagine you’re driving an electric car down the highway. Your battery is running low. You could pull off at the next exit and spend time, and energy, searching for a recharging station. Or you could simply change lanes and drive over special charging strips embedded in the road. 

That’s the vision of Khurram Afridi, associate professor of electrical and computer engineering, and his team of collaborators.

The technology would not only save time for drivers and improve productivity in warehouses. It would also literally pave the way for more sustainable transit.

“There are a lot of infrastructure questions that get asked when you say, ‘OK, we’re going to enable electric vehicles.’” Afridi said. “How does that society function? If every vehicle in the country was electric, you would need a lot of outlets to plug them in. We don’t have that kind of power available in our homes to be able to charge them very fast.”

In the system Afridi’s team has designed, two insulated metal plates on the ground, connected to a power line through a matching network and a high-frequency inverter, create oscillating electric fields that attract and repel charges in a pair of matching metal plates attached to the underside of a vehicle. This drives a high-frequency current through a circuit on the vehicle, which rectifies it. The rectified current then charges the battery.

One enormous advantage of electric fields is they have a more linear, directed nature compared with the looping arcs of magnetic fields. Hence, they do not require flux-guiding materials, such as ferrite, and can operate at much higher frequencies. The main challenge is that electric fields generated by readily available voltages are quite weak. Afridi’s team compensates by boosting the voltage and operating the system at very high frequencies to achieve large levels of power transfer.

The team’s ferrite-free system promises to be smaller, lighter, less expensive and easier to embed in the roadway. However, the system is not easy to develop.

The team’s most notable innovation is the active variable reactance (AVR) rectifier, which allows a vehicle to get full power when passing over the charging plates even if the pairs of plates – which would be laid out roughly every few meters on the road – are not completely aligned. The AVR also helps deliver power to larger vehicles that have increased clearance between their undercarriages and the ground.

If it’s tough to create a wireless charging system, it’ll be just as tough to implement it on a mass scale.

One approach, Afridi believes, would be to electrify high-traffic roadways first, especially to support large, long-haul trucks. Another option would be to focus on cities, installing charging strips at stop signs and traffic lights, so drivers could recharge while they wait.

The technology could also be employed in manufacturing warehouses and fulfillment centers so autonomous robots could work around the clock. Afridi is currently working with Toyota Material Handling North America to develop in-motion charging for forklifts and material-handling mobile robots. He is also part of a National Science Foundation-funded international research center that advances sustainable, electrified transportation.

“Wireless charging may sound crazy in the beginning,” he said. “But if we really had that technology, it would make a lot of sense.”

For additional information, see this Cornell Chronicle story.

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