It’s 92% efficient even across an 11-inch air gap.
The Department of Energy’s Oak Ridge National Laboratory (ORNL) announced recently that in late February it successfully demonstrated a new bi-directional wireless charging system, developed for medium-duty vehicles, with a bigger air gap.
The new system is able to transfer 20 kW of power across an 11-inch (28 cm) air gap at 92% efficiency in UPS’s plug-in hybrid electric delivery truck.
“The project is the first of its kind to achieve power transfer at this rate across an 11-inch air gap, advancing the technology to a new class of larger vehicles with higher ground clearance.”
According to ORNL’s Omer Onar, who led the technical team’s effort at the lab: “There’s no off-the-shelf solution that can deliver 20 kilowatts across an 11-inch air gap with these efficiencies.”
“The technology takes energy from the grid and converts it to direct current (DC) voltage. Then a high-frequency inverter generates alternating current (AC), which in turn creates a magnetic field that transfers power across the air gap. Once the energy is transferred to the secondary coil across the air gap it is converted back to DC, charging the vehicle’s battery pack.
The system incorporates ORNL’s custom electromagnetic coil design and controls system, as well as wide bandgap power conversion systems.”
ORNL developed its first wireless charging system in 2016, but it was then envisioned for cars. The 20 kW was 90% efficient across a shorter air gap. Then, in 2018, it was scaled up to 120 kW and 97% efficiency across a 6-inch (15.2 cm) air gap.
As the new system is bi-directional it could turn an electric truck into mobile energy storage to support renewable energy generation or peak electricity demand. ORNL notes that 50 trucks connected simultaneously would provide up to 1 MW of power.
“With its bi-directional design, the system also supports use of the vehicle’s batteries for energy storage. Doing so would give energy flexibility to a fleet owner’s business, and help better manage on-site generation such as solar power.”
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