SAE Blog Text

SAE J2954 TF decides upon “Differential Inductive Positioning System” as alignment methodology in upcoming standard; finalizing set of requirements needed for mass production.

Posted: November 21, 2023
Guest Post by Jesse Schneider, CEO and CTO at ZEV Station, chair of the SAE Wireless Power Transfer Task Force

Wireless Power Transfer (WPT) following SAE J2954 enables fully automatic wireless charging solutions for electric vehicles and promises highly efficient charging (up to 93%) of electric and plug-in-hybrid vehicles. The missing piece of standardization of light duty WPT has been the specification of an alignment methodology which works in all weather conditions and environments, and ensuring it is interoperable between many different types of applications. The SAE Wireless Power Transfer & Alignment Taskforce has surveyed its members including vehicle automakers, TIER 1s, OEMs and wireless charging suppliers to determine a minimum common method for alignment (fine alignment, pairing, and alignment check) to be standardized. After a comprehensive testing program, and background information, the taskforce agreed to a common alignment method for all public ground-side infrastructure called “Differential Inductive Positioning System” or DIPS for short.

The DIPS J2954 standard alignment system is described as a standardized magnetic field generated from the ground assembly with multiple coils that can be evaluated by the vehicle assembly for positioning. A conformance test is done to ensure interoperability between vehicle and charging pad. Ground and Vehicle WPT assembly manufacturers can develop and test their systems according to this interoperability specification. The DIPS transmitter and receiver coils can be fully integrated into the GA and VA.

The basic interoperability working principle of DIPS is comparable with that of the plug. The GA provides a H-field source description like the socket and the VA has therefore free choice like the connector. With that concept it is possible to develop the GA and VA independent from each other.

The H-field description is provided by a Test Station GA where a solenoid coil shown in yellow is wound around the ferrite and the litz wire from the power transfer coil to generate a horizontal field with a defined magnetic flux with 0.26 At_RMS (far below ICNIRP limit). This horizontal field allows the VA to evaluate the magnetic field early enough before reaching the Ground Assembly so that it is possible to provide the needed information about steering and braking for the driver in good time. The four red coils placed above the winding and the ferrite from the power transfer coil generate a vertical field, also with a defined magnetic flux. Since there are different frequencies, the VA can distinguish from which coil which signal level comes to calculate the position. As one example for the VA, the magnetic field can be evaluated by a crossed solenoid coil wound around the ferrite with 45° to driving direction (with only one turn each).


DIPS fine alignment/guidance solution for static charging in SAE J2954(courtesy of MAHLE)


The updated SAE J2954/1 light duty vehicle WPT standard is planned to be published in the first quarter 2024 along with a data report (on two competing methodologies) presented at SAE World Congress.

“The standardized alignment method “DIPS”, makes it easy for a seamless, all-weather J2954 wireless EV charging & parking and opens the door also for autonomous vehicles. With this, the SAE team has solved the missing link for wireless charging commercialization,” stated Jesse Schneider, chair of the SAE Wireless Power Transfer Task Force (ZEV Station).

“Wireless charging effectively provides an electric vehicle with infinite range. Just park and forget—the vehicle is always charged.  With this update to the standard, wireless automatic charging will become available to public infrastructure. I’m pleased to commend the excellent work of the SAE J2954 technical sub-committee for alignment and controls on the extended efforts to reach this result,” stated Ky Sealy, co-chair of the SAE J2954 Alignment and Controls sub-team (WiTricity).