Polyphase Wireless Transfer for EV Charging Reaches New Levels at ORNL 

ORNL’s Omer Onar, left, power electronics research lead, discusses the 270-kW wireless charging system’s lightweight polyphase electromagnetic coupling coil, pictured in foreground, with Lee Slezak, center, DOE’s Vehicle Technologies Office technology manager for grid and charging infrastructures. Credit: Carlos Jones/ORNL, U.S. Dept. of Energy. 

Using polyphase electromagnetic coupling coils with rotating magnetic fields to boost the power, researchers at the U.S. Department of Energy’s Oak Ridge National Laboratory have demonstrated breakthrough performance for wireless charging of electric vehicles. A recent series of prototype demonstrations have established the effectiveness of the technology, which ORNL is seeking to license to manufacturers. More research is focused on developing even higher power levels suitable for larger vehicles, getting the system to mass production-level readiness and exploring more applications. 

In June, the researchers demonstrated the first 270-kW wireless power transfer to a light-duty electric vehicle. Conducted on a Porsche Taycan in collaboration with Volkswagen Group of America, it surpassed a 100-kW charging demonstration performed on a Hyundai EV only two months earlier. 

“In the past three months, the ORNL vehicle power electronics and electric drives research teams have set impressive world records for wireless charging,” said Lee Slezak, DOE’s Vehicle Technologies Office technology manager for grid and charging infrastructures. “These achievements will further speed up the adoption of electric vehicles in the U.S.” 

As a light-duty passenger vehicle, the Porsche Taycan would be difficult to equip using conventional large, heavy wireless power transfer systems. The vehicle can’t support the charging hardware due to space, weight and volume limitations. Existing wireless charging systems for light-duty vehicles are currently under development for up to 11-kW power levels with up to 92% efficiency. Current industry standards cover up to 20-kW power levels.  

The ORNL-invented system that transferred power to the Porsche uses lightweight polyphase electromagnetic coupling coils with a diameter just over 19 inches that allow for higher power density in the smallest coil possible. The process is similar to the wireless charging of small consumer devices, but the unique geometry and design of the polyphase coils enable the transfer of extremely high power levels using rotating magnetic fields generated by the coil phase windings to boost the power. The charging system was seamlessly integrated into the undercarriage of the vehicle. 

The technology also includes protection systems that prevent exceeding voltage and current limits, overheating and short-circuiting. These systems can initiate shutdown procedures in the event of power interruptions or other unexpected conditions that would interfere with safe power transfer. 

ORNL researchers collaborated with Volkswagen Group of America to demonstrate the wireless 270-kW power transfer to a Porsche Taycan. Credit: Carlos Jones/ORNL, U.S. Dept. of Energy 

“The receiver coil designed for the Porsche Taycan research vehicle can achieve 8 to 10 times higher power density compared to existing systems,” said ORNL’s Omer Onar, leader of the Vehicle Power Electronics group and lead researcher on the Porsche demonstration. “Per kilowatt weight, this is also the most lightweight charging system in the world.” 

Power density is important in wireless charging because it indicates how much power the system can handle relative to its size. The goal is to achieve higher densities from smaller, more compact systems to improve overall efficiency and performance. ORNL’s system can achieve a 50% increase in state of charge within 10 minutes with more than 95% efficiency. The power transfer was conducted over a 4.75-inch gap between the ground and the coil mounted to the underside of the vehicle.   

The 270-kW demonstration marks the completion of a DOE-funded project that ORNL and Volkswagen began in 2021. ORNL’s research team leveraged Volkswagen’s expertise in vehicle integration to test the new wireless charging concept on an electric vehicle with the goal of developing the highest-power density wireless charging system through a new design that focuses on rotating electromagnetic fields. These fields increase efficiency by reducing voltage and eliminating electric current ripples and field cancellations between the coil phase windings. 

Left to right: Researchers Mostak Mohammad, Emrullah Aydin, Veda Galigekere, Omer Onar, Subho Mukherjee and Andrew Foote were part of the team that coordinated the development and demonstration of ORNL’s record-setting 270-kW wireless power transfer to a light-duty passenger vehicle. Credit: Carlos Jones/ORNL, U.S. Dept. of Energy 

“It’s exciting to see the significant progress Volkswagen and Oak Ridge National Lab are making together in many critical technologies. Innovation projects being researched in East Tennessee will transform the automotive industry,” said Lyndon Lie, Volkswagen Group of America’s chief engineering officer. “Wireless charging like that demonstrated with Oak Ridge could make charging EVs significantly easier for consumers, with quick charging times encouraging zero emissions adoption and leading to a more sustainable transportation sector.” 

Onar said ORNL and Volkswagen plan to continue working together in the near term to further improve upon the 270-kW charging prototype by developing it into a more cost-effective and manufacturable system. “We’re also working with Volkswagen on developing a polyphase system for residential charging applications and collaborating on the development of a lightweight enclosure design that will improve mechanical, electrical, thermal and magnetic performance,” Onar said. “Our goal is to mature the technology so that it’s ready for deployment in production vehicles.” 

ORNL researchers have been demonstrating improvements in wireless charging for the past decade, achieving a 20-kW transfer to a sports utility vehicle in 2016 with a charging system that utilized an ORNL-built inverter and coupling technologies. In 2018, the research team raised the mark to a 120-kW charge using conventional coil technology in benchtop lab testing. The 100- and 270-kW demonstrations mark the first time ORNL’s polyphase system has been tested on electric vehicles. “We’re working to reach much higher charge rates for other types of vehicles, including investigating achieving a significantly higher charge for heavy-duty freight and transport trucks,” Onar said. 

Volkswagen Group officials visited ORNL to view the lab’s novel lightweight polyphase electromagnetic charging system, capable of transferring unprecedented power to electric vehicles. Credit: Carlos Jones/ORNL, U.S. Dept. of Energy 

“This achievement gets us one step further to the reality of a future where an electric vehicle can pull into a charging station and recharge in the same time it would take to walk into a store and grab a snack,” said ORNL’s Burak Ozpineci, corporate fellow and distinguished researcher who leads vehicle and mobility systems research. “The driver doesn’t have to do anything but park. We’re even exploring ways that this technology could be used to charge a vehicle in motion on the roadway.” 

The novel polyphase electromagnetic wireless system was built and developed by researchers in the Power Electronics and Electric Machinery Laboratory at DOE’s National Transportation Research Center at ORNL. The electric vehicle demonstrations were conducted in the Grid Research Integration and Deployment Center there. 

At the earlier demonstration in June, the researchers showed that a light-duty passenger electric vehicle can be wirelessly charged at 100-kW with 96% efficiency using the polyphase system. It transferred power to a Hyundai Kona EV across a five-inch airgap in a process similar to the wireless charging of small consumer devices. 

ORNL’s lightweight polyphase electromagnetic coupling coil design, with a diameter just over 14 inches, achieved the 100 kW stage with higher power density in smaller coils boosted by rotating magnetic fields generated by coil phase windings. Credit: Genevieve Martin/ORNL, U.S. Dept. of Energy 

“We’ve achieved the highest power density in the world for a wireless charging system for this class of vehicle,” ORNL’s Onar said about that demonstration. “Our technology reaches power densities 8-10 times higher than conventional coil technology and can increase battery charge state by 50% in under 20 minutes.” While researchers previously achieved a 120-kW charge using conventional coil technology in benchtop lab testing, this test marked a milestone achievement for vehicle integration using ORNL’s polyphase coils. “This is a breakthrough achievement and opens the door to fast and efficient wireless charging for passenger electric vehicles,” Onar said.  

For more info, see www.ornl.gov and, for info about licensing, email partnerships@ornl.gov