Researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL) have demonstrated a 120-kilowatt wireless charging system for vehicles—providing six times the power of previous ORNL technology and a big step toward charging times that rival the speed and convenience of a gasoline station fill-up.

The wireless system transfers 120 kilowatts of power with 97% efficiency, which is comparable to conventional, wired high-power fast chargers. In the laboratory demonstration, power was transferred across a six-inch air gap between two magnetic coils and charged a battery pack.

ORNL researchers used computer simulations to design coils that generate the magnetic field required for wireless power transfer.

ORNL researchers created and demonstrated the world’s first 20-kilowatt wireless charging system, which is being modified for applications such as commercial delivery trucks. (Earlier post.)

It was important to maintain the same or smaller footprint as the previous demonstration to encourage commercial adoption.

We used finite element and circuit analyses to develop a novel co-optimization methodology, solving the issues of coil design while ensuring the system doesn’t heat up or pose any safety issues, and that any loss of power during the transfer is minimal.

—project lead Veda Galigekere of ORNL’s Power Electronics and Electric Machinery Group

To achieve 120 kilowatts, the ORNL team created a new coil design co-optimized with the latest silicon carbide power electronic devices for a lightweight, compact system.

The system’s architecture takes energy from the grid and converts it to high-frequency alternating current, which generates a magnetic field that transfers power across a large air gap. Once the energy is transferred to the secondary coil, it is converted back to direct current and stored in a vehicle’s batteries.

The demonstration advances DOE’s extreme fast-charging goal to develop a system that delivers 350 to 400 kilowatts and reduces the charging time for electric vehicles to 15 minutes or less.

ORNL researchers will explore innovations to increase power transfer level to 200 and eventually 350 kilowatts, while refining dynamic wireless charging technology.

A dynamic system enables the automatic charging of electric vehicles using wireless charging pads installed under roadways; higher power charging systems are needed to minimize the cost and complexity of dynamic charging. The goal is dynamic charging at highway speeds, Galigekere said.

The research was funded by DOE’s Vehicle Technologies Office (VTO) and performed at the National Transportation Research Center, a DOE user facility at ORNL.