Communication between Plug-in Vehicles and the Utility Grid 2010-01-0837

This paper is the first in a series of documents designed to record the progress of the SAE J2293 Task Force as it continues to develop and refine the communication requirements between Plug-In Electric Vehicles (PEV) and the Electric Utility Grid. In February, 2008 the SAE Task Force was formed and it started by reviewing the existing SAE J2293 standard, which was originally developed by the Electric Vehicle (EV) Charging Controls Task Force in the 1990s. This legacy standard identified the communication requirements between the Electric Vehicle (EV) and the EV Supply Equipment (EVSE), including off-board charging systems necessary to transfer DC energy to the vehicle.

It was apparent at the first Task Force meeting that the communications requirements between the PEV and utility grid being proposed by industry stakeholders were vastly different in the type of communications and messaging documented in the original standard. In order to understand and adequately capture the communication structure between plug-in electric vehicles and the electric power grid, the task force generated two new documents. The original J2293 was also re-issued to keep it intact for legacy equipment.

The two new SAE documents are J2836™ and J2847. SAE J2836™ is an Information Report that captures the communication requirements between plug-in electric vehicles and the electric power grid based on use cases. A use case is simply a "story" that includes various "actors", and the "path" they take to achieve a particular functional goal. By considering the actions of the actors working to achieve this functional goal, a completed use case results in the documentation of multiple scenarios, each containing a sequence of steps that trace an end-to-end path. These sequential steps describe the functions that the proposed systems and processes must provide, directly leading to the requirements for the given use case.

SAE J2847 is a Recommended Practice which builds upon the Use Cases defined in J2836™ and defines the detailed messages and specifications for vehicle to utility communication.

Both SAE J2836 & J2847 have a series of dash 1 through dash 5 in order to keep the task force focused as we start, beginning with the fundamental requirements and migrate to other more advanced options. Dash 1 identifies the Utility rate and incentive programs, dash 2 includes the detail for an EV Supply Equipment (EVSE) for off-board DC chargers (updated version of J2293), dash 3 is for reverse energy flow, dash 4 includes diagnostics of the charging system and PEV and dash 5 contains vehicle manufacturer specific options.

The primary purpose of SAE J2836™ and J2847 is to achieve grid-optimized energy transfer for plug-in electric vehicles - that is, ensuring that vehicle customers have sufficient energy for driving while minimizing system impact on the electric grid. This can be accomplished, for example, by voluntary participation in utility controlled-charging programs in return for financial incentives, and hence the specification therefore supports information flows that enable such mechanisms.

These specifications support energy transfer via both Forward Power Flow (FPF) (grid-to-vehicle), and Reverse Power Flow (RPF) from vehicle-to-grid. Forward Power Flow is used to charge the vehicle's rechargeable energy storage system (RESS); support for FPF is optional, though encouraged, for any plug-in vehicle implementation. Reverse Power Flow may be used to discharge the RESS, in order to provide support to the grid, or to power local loads during a grid outage; support for RPF is also optional and may be limited with various RESS applications.

Beyond its primary purpose of energy transfer, these documents enable other applications between vehicles and the grid, such as vehicle participation in various utility rates and incentive programs, utility-controlled charging plans (e.g., Demand response and direct load control), and participation in a Home-Area Network (HAN) of utility-managed electrical devices. The protocol established is designed to be extensible, so that as new applications emerge, additional messages can be added while maintaining support for the existing message set.