New Audi A3 sedan offers 48V MHEV, diesel powertrains
Faradion receives first order for sodium-ion batteries for Australian market

ORNL demos 20 kW bi-directional wireless charging on UPS PHEV truck; 11" air gap, >92% efficiency

Researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL) in late February demonstrated a 20-kilowatt bi-directional wireless charging system installed on a UPS medium-duty, 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.

UPS Demo rear view

ORNL’s wireless charging technology transferred power between the truck and a charging pad across the 11-inch gap using two electromagnetic coupling coils at the demonstration. The system transferred electricity from the power grid to the vehicle battery terminals at more than 92% efficiency.

At a 20-kilowatt level, it would take about three hours to charge the vehicle’s 60-kilowatt-hour battery packs. Conventional wired charging typically takes between five to six hours using the existing onboard charging system.

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. ORNL’s bidirectional technology is fully compliant with grid power quality standards.

“Scaling the technology to a fleet of 50 trucks gives you megawatt-scale energy storage,” noted ORNL’s Omer Onar, who led the technical team’s effort at the lab.

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. The technology was tested using grid and battery emulators before integration into the vehicle, utilizing two unique facilities at ORNL: the DOE National Transportation Research Center user facility, and the lab’s Grid Research Integration and Deployment Center.

The project leverages ORNL’s expertise in vehicle systems integration as well as power electronics engineering.

There’s no off-the-shelf solution that can deliver 20 kilowatts across an 11-inch air gap with these efficiencies.

—Omer Onar

The technology “represents an integrated, holistic solution for vehicle electrification that also advances the next-generation smart grid,” Onar added. “The system expands the possibilities for fleets who want convenient, efficient EV charging as well as electricity storage solutions.”

UPS appreciates the Department of Energy’s support on this effort. This project demonstrates innovative ways to utilize vehicle battery storage at fleet scale to power the vehicle, add resiliency to our facilities and support the grid.

—Mike Whitlatch, vice president of Global Energy and Procurement for UPS

Oak Ridge researchers first demonstrated a 20-kilowatt wireless charging system on a light-duty passenger vehicle in 2016. The technology for light-duty applications has since been scaled up to 120 kilowatts, advancing the goal of wirelessly charging a typical consumer’s electric vehicle in about the same time as a gas station fill-up.

The technology is undergoing further testing and analysis as part of the project, which is supported by the DOE Office of Energy Efficiency and Renewable Energy’s Vehicle Technologies Office.


Jason Burr

Can someone explain to me why they take AC from the grid source, convert to DC, then use an inverter to change back to AC to create a magnetic field? Or is the article trying to say that the process of creating the magnetic field does it as AC (the process is intertwined)?

Three hours seems a little long for UPS, but how is it 5-6 hours for plugging in? I could see fleets install these at docks so the trucks recharge while being reloaded. Though 3 hours seems a little too long for how fast UPS turns and burns.



Transmitting power via induction requires a time-varying field.  The voltage induced is directly proportional to the rate of change.  60 Hz is way too slow to move significant power across a foot-wide air gap; these chargers appear to run in the low radio frequencies of tens or hundreds of kHz.  Converting line power to DC and re-inverting to radio frequencies is just the most convenient way to go about this.  I suppose you could run the RF gear on raw rectified AC power a la a Tesla coil, but it's probably easier to design it for a constant supply voltage.

Account Deleted

The 5-6 hours for plugging means that at night they are using level 2 Chargers (7.7 kW max).
Not mentioned in the GCC post is that these are Workhorse Plug-in Hybrid E-GEN delivery vans that Workhorse builds for UPS. They use the 2 cylinder range extender engine from the BMW i3 REx. They would be turned on for long trips (up to 400 mile range) and cost the same as the diesel delivery van.

Also, ORNL has already developed 120 kW wireless chargers. So if the batteries can handle the fast charge then charge times would drop to maybe 15 minutes for a 20 kWh charge for midday stops at the warehouse.


Is the 8% loss emitted as RFI radiation? At almost 2kW RFI radiation is rather large. I wonder how that going to meet EMC standard.

Account Deleted

Is the 8% loss emitted as RFI radiation?
That is a good question. Most of the loss is probably related to the transmitting coil, receiving coil, and power electronics (ORNL is going to silicon carbide in the 120 kW version which is 99% efficient).
ORNL is required to meet C95.1-2019 - IEEE Standard for Safety Levels with Respect to Human Exposure to Electric, Magnetic, and Electromagnetic Fields, 0 Hz to 300 GHz.

You can read more in the article "ORNL Experience and Challenges Facing Dynamic Wireless Power Charging of EV’s" where they state:
The effects of EMF leakage fields on persons within proximity to the WPT apparatus drove the ORNL choice of multiple coils and a means of sequencing in lieu of a continuous primary loop feed by a HF current source. Reference website:


This is to address the question on 8% loss. The 8% loss is not the RFI radiation. Our efficiency number is the overall efficiency of the system. The >92% efficiency is all the way from grid to the vehicle battery terminals including the losses on the grid-interface converter, high-frequency inverter, primary and secondary couplers (coil-to-coil losses), primary and secondary resonant tuning passive components (inductors and capacitors), secondary(vehicle)-side rectifier/inverter, and all the cabling, fusing, contactors, connectors, etc. There are 4 power conversion stages and coil-to-coil is only one of them. Also, not all of the coil-to-coil losses are due to the electromagnetic field emissions (fringe/stray fields). There are still copper (conduction) losses in the coils.

The comments to this entry are closed.