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New SAE J2847/2 Revision

The Journey to Settle the Question: How do we offer an immediate and simple standardized solution for DC Vehicle to Grid and Vehicle to Home?

Guest Post by Richard Scholer, Manager – Charging Systems at Stellantis
Posted: September 5, 2023

Buying an electric vehicle, you are presented with a myriad of options and features. One such feature is bidirectional charging or V2X options. Do you choose Vehicle to Load (V2L), Vehicle to Vehicle (V2V), Vehicle to Grid (V2G) or Vehicle to Home (V2H) or combinations of these or all of them? These features are expected to be explained to the EV owner at the dealerships, thru their local utilities and other sources.

Updating SAE J2847/2 was the first step for DC V2G and V2H for vehicle OEMs to offer a Standard solution that multiple OEMs and Charging station suppliers can offer and various vehicles and charging stations will be interoperable. DC V2G/V2H means the bidirectional inverter is in the offboard charging station.

This starts with J2847/2 using the same communication code as is presently used for DC charging and identifies how to apply negative signals for Power and Current that are matched between the vehicle and charging station during the initialization phase of message exchange. This update also identifies the complete requirements for the home that needs to be considered, such as the home main utility panel that may need some changes, adding an Automatic Transfer Switch (ATS), the same as a home generator would require. A home balancing transformer may also need to be added for V2H since the home is no longer connected to the utility transformer to balance the 120VAC phase circuits, unless this balancing function is a part of the Bidirectional DC charging station. These are choices on implementation, but the design needs to include them and this is clearly stated in the standard. Additional communication from the ATS to Charging station along with back up power for communication is also included.

The SAE standards identify the complete system and include “what to do”, not “how to do it” so each system or sub-system can determine the amount of integration of components to meet the overall requirements for their equipment. The home system needs to meet these requirements and the vehicle needs to interact with the DC charging station with the same interface.

SAE J2847/2 focuses on DC V2G/V2H since the bidirectional inverter is offboard the vehicle.

J2847/3 has also been updated for AC V2G/V2H and is in the final ballot cycle. There are choices for the customer to choose an DC or AC system and important for both standards to be in place.

If a customer is installing Solar and/or Stationary storage, these are also DC systems and a DC charging station may have appeal since these are all converting DC energy to DC energy between these and then may have a single inverter to convert to AC to send energy into the home.

If not, then an AC system may be the best choice since it may be less cost than a stand-alone bidirectional DC charging station. The vehicle onboard charger however then has to include the additional features to meet the state regulations and utility company requirements.

Whether the bidirectional inverter is offboard (DC V2G) or onboard (AC V2G), it is required to meet additional grid stability functions such as voltage, frequency adjustments and more. J2847/3 complements the Sunspec Profile standard that that identifies the steps and exchange of messages when the vehicle connects to the AC charging station installed in the home.

The vehicle OEM identifies these requirements to the customer when they select a vehicle with these options and any additional interaction with their utility provider, along with options to engage local installers to provide the complete home solution. The SAE standards include the entire system at this time but when other standards include some of this material, SAE will be updated and then reference those other standards, instead of duplicating material.

The SAE Hybrid Communication and Interoperability Task Force did not stop with V2H and V2G, J2847/5 is also in the final ballot cycle for AC V2L and AC V2V. This completes the entire V2X features for OEMs and equipment suppliers have standards in place for their designs and products. This provides common solutions for customers to select various OEM vehicles and equipment and use interoperable product. V2L applies to remote sites to power tools, equipment, camp sites and more, where there is no grid power. V2V offers a Jump start to another electric vehicle that may need a small amount of energy to drive to a charging station, similar to providing a gasoline vehicle a gallon of gas to drive to the nearest gas station.

This is still not the end of this effort as the Task Force is now updating J3072 for vehicle onboard inverter requirements and J2846/3 for V2X use cases. Hank McGlynn is leading these, and the updates are intended to harmonize with the added features noted above and other standards in IEEE and UL along with regulations that have continued to change.

Additional updates are planned to J2847/2 and J2847/3 to include Solar and/or Stationary Storage for the V2H function since one of these three devices need to function as “grid forming” or generate the home voltage and frequency, and the others would be “grid following” or match this voltage and frequency and simply add power to the home if loads require it. Coordination of the controls and power and perhaps the transfer of this function from one device to another also needs to be clear.

This is a first step for V2X updates and provides a complete set of standards and recommended practices for all the V2X functions. These will continue to be updated as the regulations change, and customer expectations continue to evolve for these new uses of Electric Vehicles.