ORNL Researchers Bring Wireless EV Charging to Fruition

July 07, 2021 by Ahmad Ezzeddine

Oak Ridge National Laboratory scientists were able to deliver high power in wireless battery charging technologies after several years of research.

As electric vehicles become more common, research groups are looking to make the charging of these vehicles more convenient and efficient.

The dynamic wireless charging test bed at ORNL accelerates an innovation that will charge electric vehicles while they’re being driven along specially equipped roadways. Image courtesy of Carlos Jones (ORNL/U.S. Dept. of Energy)

An electric vehicle is charged by either plugging it into an external power source or could be charged using wireless charging technology. For a vehicle to be wirelessly charged it must have a power receiver. Note that the efficiency of a wireless charging system is determined by the total power delivered to the receiver over the total power transmitted.

Their air gap between transmitter and receiver is an important term where it could affect the efficiency of the system. ORNL researchers developed a system that serves light-duty passenger cars at a 6-inch gap and medium-duty trucks at an 11-inch gap. The system has a high power transfer efficiency, over 92%, at the 20 KW level. 

This system also provides reverse charging so that the power could be transmitted back from the vehicle to external use. This allows vehicles to grid energy transfer where the vehicle energy could be sold when the energy price is at its peak. More important are the vehicles to house energy transfer, an electric vehicle could be used as a power supply during utility blackouts.


Three Levels of Charging

There are three levels in which a vehicle could be charged according to the battery size and the charging units. The three levels of charging are slow, fast, and rapid. Slow charging units are rated up to 6 KW and could take up to 12 hours to charge a unit. Fast chargers are rated up to 25 KW and could fully charge a 40 kWh battery within 2.5 hours. Rapid charging is the fastest to fully charge a battery where a 50 KW charging unit can fully charge an electric vehicle in an hour.

After demonstrating a 120 KW/ 97% efficient charging system, the researchers aim to install 15 minute charging systems on passenger vehicles with a power of up to 270 KW.


Dynamic Wireless Charging

Dynamic wireless charging is a system that the researchers at ORNL developed that can automatically charge vehicles on specially equipped roadways. Dynamic charging uses charging pads that could charge the vehicle while driving over it. If equipped on highways, a vehicle could get charged while running over the highway. The researchers aim for a 200 KW system to be installed on highways, therefore, charging many cars, therefore, being financially efficient.


Research Group Efforts

The Grid Research Integration and Deployment Center at ORNL was used to demonstrate medium-duty vehicle wireless charging.

The National Transportation Research Center at ORNL was used to evaluate and build the systems.

The DOE Office of Energy Efficiency and Renewable Energy’s Vehicle Technologies Office supported this research.