SAE International has published a new global standard that specifies both the vehicle-side and charger-side requirements for wireless charging of EVs.
The new standard, SAE J2954, was more than a decade in the making. In 2007, when SAE began its research, there were few EVs on the market, and wireless power transfer (WPT) may have seemed a whimsical pursuit. Since then, the Wireless Power Transfer and Alignment Taskforce has worked to thoroughly vet and test the technology, in partnership with numerous government agencies, regulatory bodies and industry groups.
Wireless power transfer begins with parking a vehicle over an SAE J2954-compatible transmitting pad on the ground (the Ground Assembly, or GA). After a communications handshake, charging begins automatically. Power is transferred by creating a magnetic resonance field between the GA and a receiving pad fitted on the underside of the vehicle (the Vehicle Assembly, or VA). The energy crosses an air gap (the ground clearance between the pads) and is then converted from AC into DC on the vehicle to charge the battery pack.
Tests using a 10-inch ground clearance have shown that WPT systems can operate at grid-to-battery efficiencies of up to 94%.
“Charging your EV should be as simple as parking and walking away. The SAE J2954 standard gives freedom and convenience to do exactly that, safely and automatically,” said Task Force Chair Jesse Schneider. “The SAE J2954 standard is a game-changer by giving a ‘cook book’ specification for developing both the vehicle and charging infrastructure wireless power transfer as one system, compatible to 11 kW. The SAE J2954 alignment technology gives additional parking assistance, even allowing for vehicles to park and charge themselves autonomously.”
The new standard specifies three power levels: WPT1 (3.7 kW), WPT2 (7 kW), and WPT3 (11 kW). To validate its performance targets and safety limits, the standard includes key parameters such as minimum efficiency, limits on electromagnetic interference (EMI), and foreign object detection. There are three overlapping ranges of vehicle ground clearances, from 100 to 250 mm (3.9 to 9.8 inches) and three levels of grid input to the GA, up to 11.1 kVA. Parking tolerances are ±75 mm (3.0 inches) in the direction of travel and ±100 mm (3.9 inches) in the lateral direction.
Wireless communication for control of the WPT charging process was standardized by SAE J2847/6, which was published in 2015, and updated in 2020. “SAE J2847/6 is a communications document utilizing WiFi, IEEE 802.11n, designed specifically with the SAE J2954 standard, and facilitates the automatic wireless charging experience while allowing for continuous optimization of the WPT system,” said Ky Sealy, co-lead of SAE J2847/6.