SAE approves wireless charging guidelines for plug-in electric vehicles

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Wireless charging is expected to be a large part of the future of electric vehicles(Credit: BMW)

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The Society for Automotive Engineers International has approved publication of its first wireless charging guidelines. The "SAE TIR J2954 Wireless Power Transfer for Light-Duty Plug-in/Electric Vehicles and Alignment Methodology" paves the way towards an industry-wide wireless charging standard for automobiles.

The current SAE J1772 standard has created an industry standard for plug-in charging that has been adopted by a large number of automakers. The TIR J2954 wireless standard has co-signers that include Daimler, BMW, Fiat-Chrysler, Ford, General Motors, Honda, Jaguar Land Rover, Mitsubishi, Nissan, and Toyota. Those co-signers make up the bulk of the plug-in vehicles being produced today. Several Tier 1 original equipment manufacturers such as Delphi, LG, Panasonic, TDK, and more have also signed onto the new SAE guidelines. Manufacturers of plug-in systems for buses, such as Volvo, BYD, and Proterra, are also co-signers.

The new SAE standard is meant to create a basis for wireless charging protocols for passenger vehicles. It creates a wireless power transfer (WPT) protocol for low-speed charging and leaves openings for addenda that can accommodate higher-speed charging options. The paper includes a test setup for WPT acceptance and has been in the works since the SAE Wireless Power Transfer committee was was formed in 2010. That committee is chaired by BMW's Fuel Cell, Electric Vehicle and Standards Development Manager, Jessee Schneider, who presented the paper, which will be published online on May 31, 2016, at an electric vehicle conference in Logan, Utah.

SAE TIR J2954 establishes 85 kHz (81.39-90 kHz) as a common frequency band for light-duty vehicle charging systems. Four levels of plug-in and electric (PH/EV) WPT are defined in the guidelines with more allowed in future revisions. Specifying the frequency band allows manufacturers to build wireless charging receivers in vehicles that are compatible with multiple wireless charging stations from various makers. Just as the J1772 standard has allowed a Nissan and Mitsubishi to both utilize the same charging plug, so will the J2954 standard allow a Toyota and a BMW to also share wireless stations.

The four charging levels are labeled WPT 1-4, with two being defined in the current paper and two more reserved for future use. WPT 1 specifies 3.7 kW charging capability (speed) and WPT 2 specifies 7.7 kW capability. These two charging classes are now being tested in the United States by a Department of Energy team from Idaho and Argonne National Labs. Bench testing is currently underway and live in-vehicle testing on infrastructure-based grids is on its way, with a 2018 target for completion of the standard.

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