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SAE publishes J2954 Recommended Practice (RP) enabling wireless charging to 11 kW

SAE International published SAE J2954 Recommended Practice (RP), providing the first worldwide specification for wireless power transfer (WPT) for electric vehicles up to 11 kW power levels (WPT 3). Following the previous Technical Information Report J2954, with power levels up to WPT 2 (7.7 kW), 11 kW wireless charging is a big step towards commercialization for electric vehicles. (Earlier post.)

The RP also provides a standardized test stand (first up to WPT 2 power levels) which gives both electric vehicle manufacturers and infrastructure companies a means for testing performance and validation of products and new developments. The J2954 standard test stand is based on the circular topology but also provides a way to demonstrate compatibility to other topologies such as the “double D” design.

SAE J2954 RP Picture 1 copy

Inductive WPT systems have two main components; a Ground Assembly (GA) unit and a Vehicle Assembly (VA) unit. The GA contains a grid-connected Power Factor Correction (PFC) converter, followed by a DC-AC inverter, a filter and impedance matching network (IMN) connected to the GA coil. The VA consists of the VA coil connected to an IMN and filter, a rectifier and an optional impedance converter that produces suitable voltages and currents to the connected battery. During charging, the magnetic energy created by the GA Coil is coupled to the VA Coil.

Sae1
WPT systems consist of a Ground Assembly (GA) and a Vehicle Assembly (VA). The GA broadly consists of a main connected Power Factor Correction (PFC) converter, followed by a DC-AC inverter, a filter and impedance matching network (IMN) that is connected to the GA coil. The magnetic energy created by the GA Coil is coupled to the VA Coil. The VA consists of the VA coil connected to an IMN and filter, a rectifier and an optional impedance converter that produces suitable voltages and currents to the connected battery. —SAE J2954. Click to enlarge.

The Recommended Practice establishes a new methodology using magnetic triangulation for vehicle alignment to assist manual as well as autonomous parking. Coupled with communications, SAE J2954 can assist EV drivers seamlessly to park their vehicles, to establish payment and to charge without customer interaction.

Image LPE J2954
Wireless charging is convenient due to its non-contactless nature. One of the benefits of wireless charging is the flexibility provided in alignment between the charging infrastructure and a vehicle. While fairly large tolerances may be allowed, some level of vehicle alignment is required in order to ensure safe and efficient charging. It is primarily the responsibility of the vehicle’s on-board capability to guide or otherwise assist the driver in aligning the Vehicle Assembly to the Ground Assembly. There is a need, however, for a standardized method to allow for any vehicle with a SAE J2954 compliant VA Coil to align with any SAE J2954 compliant GA Coil.

The SAE J2954 alignment sub-team has surveyed vehicle OEMs and wireless charging suppliers to determine the minimum common method of alignment to be standardized. The adopted minimum common alignment method is by means of low power excitation (LPE). LPE is the method whereby the SAE J2954 compliant GA coil is excited at a low current to induce a detectable signal on the VA. —SAE J2954. Click to enlarge.

Power transfer enables vehicle ground clearance up to 250 mm (10 inches) with a side-to-side tolerance of +/- 100mm (+/-4 inches). The alignment method assists the driver to stay within the charging range—and autonomous vehicles with finding parking spots—even in inclement weather like rain or snow.

The RP SAE J2954 provides EMF & EMC limits as well as test methodologies for conformance which have been vetted with the American Association of Medical Instrumentation, US FDA as well as internationally with CISPR B.

SAE International also published a technical paper with bench test results from the automobile and wireless charging suppliers measured at the US DOE’s Idaho National Labs and TDK. This test report confirmed that operation with both matched and unmatched coil topologies, as well as charging between different power ranges (3.7kW to 7.7kW), power transfer can be achieved at full power and with high efficiency up to 93% (grid to battery). Over the next year (2018), the systems will be tested—including in-vehicle field testing—for a final validation. Thereafter, the standard will be released.

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Va1
Two examples of vehicle assemblies (VA): (left) circular topology; (right) double D. SAE 2017-01-2448 Click to enlarge.

SAE J2954 Signage
Standardized signage has been developed to help customers quickly identify an SAE J2954 parking space with a recognizable design as well as the delivered power level. WPT 1-3 (3.7-11 kW) are specified in the published SAE J2954 RP.

The SAE J2954 RP establishes the methodology for designs and testing of wireless power transfer for EVs up to 11 kW. It does much more than that, by enabling an automated and seamless “charge-and-park” experience for the customer. Wireless power transfer using J2954 also gives the soon-to-be commercialized autonomous vehicle a way to align themselves and charge even during inclement weather automatically. Thus, it enables customers and taxi fleets a way to charge without the need for human interaction. This disruptive technology changes the game for EVs by removing the need for the customer to plug in—making the act of charging not about the plug, but parking in the right spot.

—Jesse Schneider, Chair of the SAE Wireless Power Transfer and Alignment Taskforce

Resources

Comments

Davemart

'This test report confirmed that operation with both matched and unmatched coil topologies, as well as charging between different power ranges (3.7kW to 7.7kW), power transfer can be achieved at full power and with high efficiency up to 93% (grid to battery).'

That is the first time I have seen this so definitively stated.

Great news, and if anything better than wired charging typically gets!

This is far more important for PHEVs than BEVs, and in my view combined with the lower life time GHG emissions of PHEVs against BEVs as in the report the other day moves PHEV technology into a decisive advantage.

CheeseEater88

Two words "up to", i mean yeah the shorter height vehicles will be better, than let's say a truck. I imagine proximity to the pad has to do with the efficiencies.

It would be nice to know the average efficiency not the peak.

It would be nice to have these installed flat, into the surface, so snow plows or other unforseen things like thieves would be less apt to damage them.

But as you say Dave very definitive. I was surprised by the 93%.

At 7.7kw it is good enough for PHEV but BEV might find it lacking. The question is what will be the cost compared to the other style of chargers?

Engineer-Poet

The Combo 1 connector is good for charging at up to 80 kW (400 V @ 200 A).  Charging at a fraction of that power at a substantial loss in efficiency has to be counted as a giant step backward.

Darius

Very, very important step. Much more significant than fast charging stuff. Practical wireless chwrging would enable mass charging capability at public parking locations.

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