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.
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.
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.
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.
|Two examples of vehicle assemblies (VA): (left) circular topology; (right) double D. SAE 2017-01-2448 Click to enlarge.|
||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
Schneider, J., Kamichi, K., Mikat, D., Sutton, R. et al., “Bench Testing Validation of Wireless Power Transfer up to 7.7kW Based on SAE J2954,” SAE 2017-01-2448