Tech Unplugged

ORNL researchers bring wireless charging to electric vehicles


ORNL researchers bring wireless charging to electric vehiclesORNL researchers bring wireless charging to electric vehicles (hi-res image)

Researchers at the Department of Energy’s Oak Ridge National Laboratory are using wireless technology to charge electric vehicles at rest or on the go, a development with potential to give EVs much smaller batteries and potentially limitless range.

Omer Onar and his team of research scientists at ORNL’s National Transportation Research Center are working to provide a convenient, safe and flexible wireless power transfer technology that eliminates the need to physically plug in. With an in-ground charging transfer, electric vehicle drivers can simply park their car and wake up to a fully charged battery.

“Wireless charging can be embedded in the ground,” Onar said. “There are no moving parts and it’s completely water and weatherproof.”

Onar and his team discovered that sufficient battery power can be transferred from the primary to secondary circuits without significant energy loss if the operating frequency is around the resonance frequency of the circuit, depending on the air gap between the coils, misalignment and the state-of-charge of the battery.

The electrical power is then transmitted to charge the battery, which is magnetically coupled to the secondary circuit through an air-core transformer. The charge has 91 percent efficiency over a 125 to 200mm air gap and is relatively unaffected up to 25 percent misalignment.

“Charging becomes possible at work and on the highway as the infrastructure expands,” Onar said. “First, we’ll take advantage of strategically placed charging opportunities and then we’ll get to charging on the move.”

Buses, for example, could benefit from opportunistic charging--the strategic placement of charging stations. Batteries could be smaller, which would shed weight and save money while allowing for strategic charging placement and quicker charge times.

“Predefined routes and planned stops would allow for strategic charging within minutes,” Onar said. “That keeps the shuttles moving, which in turn cuts harmful emissions that gather while the buses idle.”

Dynamic charging is, perhaps, the most exciting phase of the project. Charging a vehicle in motion gives electric vehicles essentially unlimited electric range while using a relatively small battery pack.

These dynamic charging stations would sit underneath the asphalt and charge vehicles as they pass over them, using data collected from vehicle sensors on the side of the road to determine how much charge a car's battery has.

“This dynamic charging can supply a large fraction of energy for the transportation sector and greatly reduce petroleum consumption,” Onar said.

Traffic could even be considered a good thing, as delays would allow longer charge time when the cars hover over the charging coils.

In 2012, Onar and his team at NTRC demonstrated the very first in-motion wireless charging system that uses coils to transfer power to a small electric vehicle. This year, they expanded the system and added feedback controls from the road to the vehicle. The team is looking forward to implementing the wireless charging technology in parking lots at ORNL.

“We’re still working to develop the robust nature of wireless power technology to charge electric vehicles,” Onar said. “But we’re getting there.”

Funding for the project is provided by DOE's Vehicle Technology Office.

 -  Dylan Platz,  865.576.1946,  November 04, 2013

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