A more powerful 50-kilowatt system is already being looked into

Electric vehicle wireless charging hits 90 per cent efficiency

Super-efficient wireless charging for electric cars has been demonstrated at the US Department of Energy’s Oak Ridge National Laboratory (ORNL) in Tennessee.

The 20-kilowatt charging system has been shown to achieve 90 per cent efficiency at three times the rate of the plug-in systems commonly used for electric vehicles today.

It is hoped that the greater convenience of the system will help to accelerate the adoption of electric vehicles. Industry partners from Toyota, Cisco Systems, Evatran and Clemson University International Center for Automotive Research contributed to the development of the technology.

The developers created a unique architecture that included an ORNL-built inverter, isolation transformer, vehicle-side electronics and coupling technologies over the course of three years.

The technology was trialled by integrating the single-converter system into an electric Toyota RAV4 equipped with an additional 10-kilowatt hour battery.

The researchers are already looking ahead to their next target of 50-kilowatt wireless charging, which would match the power levels of commercially available plug-in quick chargers.

Providing the same speed with the convenience of wireless charging could increase consumer acceptance of electric vehicles and is considered important for the wide adoption of hands-free, autonomous vehicles.

Higher power levels are also essential for charging larger vehicles such as trucks and buses.

However, as the energy transmitted by the system is ramped up, safety considerations need to be taken into account.

“The high-frequency magnetic fields employed in power transfer across a large air gap are focused and shielded,” said Madhu Chinthavali, ORNL Power Electronics Team lead. “This means that magnetic fringe fields decrease rapidly to levels well below limits set by international standards, including inside the vehicle, to ensure personal safety.”

The system is designed to be convenient and simple for its users and could eventually be installed in garages and driveways so that an electric vehicle could immediately start charging as soon as it is parked in its usual spot.

Radio communications are used to regulate the power consumption which is augmented by software control algorithms.

While the team’s initial focus has been on static or motionless wireless charging, the researchers have also demonstrated the system’s dynamic charging capabilities which allows vehicles to be driving and charging simultaneously.

Funding for the project was provided by the Department of Energy’s EV Everywhere Grand Challenge, which aims to make plug-in electric vehicles as affordable to own and operate as today’s gasoline-powered vehicles by 2022.

Electric vehicles are predicted to become cheaper to run than petrol vehicles in the 2020s due to the falling price of battery technology according to recent research which also claims they will make up more than a third of new vehicle sales by 2040.

“Wireless power transfer is a paradigm shift in electric vehicle charging that offers the consumer an autonomous, safe, efficient and convenient option to plug-in charging,” said David Smith, vehicle systems program manager. “The technology demonstrated today is a stepping stone toward electrified roadways where vehicles could charge on the go.”

In November, Fraunhofer researchers demonstrated a smart energy management system that allows homeowners to charge their electric vehicles from rooftop solar panels.

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