SAE規格 J2954/2, 2022: Wireless Power Transfer for Heavy-Duty Electric Vehicles

Description

The published SAE J2954 standard established an industry-wide specification that defines acceptable criteria for interoperability, electromagnetic compatibility, EMF, minimum performance, safety, and testing for wireless power transfer (WPT) for light-duty plug-in electric vehicles. This SAE Information Report, SAE J2954/2, defines new power transfer levels in the higher power ranges needed for heavy-duty electric vehicles. This document addresses the requirements based on these charge levels and different vehicle applications as a first step in the process of completing a standard that the industry can use, both for private (fleet) and public wireless power transfer, including for charging electric vehicle batteries.

This document is the first step in a process towards HD static and dynamic WPT. This document lacks specific requirements and solutions, for which field data is needed. This document is not intended to be a guideline to enable manufacturers to design systems with minimal assistance; the goal is to inform readers about many of the things to consider in addressing this market and is an outline for the SAE J2954/2 committee for continued work. Based on data, there will be much more detail in the next version of this document. This document represents experience from the SAE J2954 light-duty standard along with active participation of industry providers developing and deploying non-standardized HD wireless power transfer systems with the goal of creating standardized systems in the future.

SAE J2954/2 addresses unidirectional power transfer, from grid to vehicle; bidirectional transfer may be evaluated for a future document. This document is intended to be used in stationary applications (power transfer while vehicle is not in motion) and some dynamic applications.

SAE J2954/2 covers requirements for safety, performance, and interoperability. Further development of detailed requirements will be based on performance-based evaluations of candidate designs, including evaluations against electrical safety and human safety standards.

SAE J2954/2 also covers recommended methods for evaluating electromagnetic emissions, but the requirements and test procedures are controlled by regulatory bodies.

Wireless Power Transfer General System Description
WPT systems consist of a ground assembly (GA) subsystem and a vehicle assembly (VA) subsystem as depicted in Figure 1. The GA broadly consists of a connection to an AC or DC power source, with suitable filtering and phase correction in the case of an AC source, in order to minimize the disturbances to others sharing the power source followed by a DC-AC inverter, a filter and an 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.

In order to ensure safety, a certain set of requirements are met by both the GA and the VA, including monitoring for safe operation (voltage, current, and temperature) and the ability to take corrective action in the event that a limit indicating unsafe operation is being approached.

The GA and the VA share a communication system that allows the GA to know the state of the VA and for the GA to receive and respond to messages from the VA. It is critical that power transfer is not initiated until the GA determines that a vehicle with a compatible VA is in place and properly aligned.

The following steps describe the high-level operation of the closed loop power transfer system with respect to the sub-system blocks in the diagram in Figure 1, after necessary safety and compatibility checks have been performed and passed.

• Within the vehicle, the VA (25) determines the power desired to charge the battery and to provide power for other purposes.
• The request for power is communicated over the wireless communication channel (b) from the VA to the GA (15).
• The GA recognizes the request, draws power from the grid, converts it to high frequency AC, and sends it to the GA coil (11).
• The high frequency AC couples (a) to the VA coil (21), is rectified and processed in the VA, and delivers it to the vehicle electrical system to charge the batteries and provide power for other purposes.
• This process continues until the VA signals a different power level requirement, including no power required, as would be the case when the demand no longer exists.