Use Cases for Plug-In Vehicle Communication as a Distributed Energy Resource
|Publication Date:||1 January 2017|
This SAE Information Report establishes use cases for a Plug-in Electric Vehicle (PEV) communicating with an Energy Management System (EMS) as a Distributed Energy Resource (DER) which must be supported by SAE J2847/3. This document also provides guidance for updates to SAE J2847/2 to allow an inverter in an EVSE to use the PEV battery when operating together as either a DER or as a power source for loads which are not connected in parallel with the utility grid. Beyond these two specific communication objectives, this document is also intended to serve as a broad guide to the topic of reverse power flow.
Distributed Energy Resources are small, modular Distributed Generation (DG) or energy storage systems that provide electric power or energy where it is needed on the distribution grid. A PEV using a "utility-interactive
Even if a PEV is not capable of reverse power flow, it can still be used as a DER device to allow for active control of charging for grid purposes. The use of a variable load for grid purposes is sometimes called Demand Dispatch or Demand Management. This can be considered a single-sided use of a DER device and is no different than a generator that can only vary power output.
A PEV could also serve as a power source for tools or other devices, where grid power is not available, or provide emergency backup power for a home following a loss of grid power. These are all off-grid applications. This is all about pure reverse power flow and it can be engaged manually using controls and displays provided by the vehicle manufacturer. For these applications, the vehicle is just like a portable standby generator.
In all the discussion of the benefits of reverse power flow and the use of a PEV as a DER, it is important to always remember that the primary purpose of the energy stored in the vehicle battery is transportation. While it may be acceptable for a stationary grid storage unit to discharge all afternoon and recharge at night, a PEV participating in a V2G application may need to be fully charged by the end of the workday. The use cases for a PEV serving as a DER will need to account for two objectives: serving the grid in a V2G application and having enough energy by the time of departure to meet its transportation needs.
Figure 1 provides an overview of the purpose of the document. A stationary, grid-connected, energy storage system (ESS) is shown at the top of the diagram. It is a distributed energy resource (DER). There is a great deal of work going on to integrate ESS units into the grid. A plug-in electric vehicle (PEV) with an on-board inverter looks like the stationary ESS and can be a DER device. This system is shown in the middle of the diagram. The possible use of reverse-flow capable PEVs, as inverter-based ESS units, has generated significant interest. This potential use of PEVs has become known as vehicle to grid (V2G). Alternatively, the inverter could be located externally in the electric vehicle supply equipment (EVSE) in which case the PEV battery is only used to supply or absorb DC power as required by the inverter. This system concept is shown at the bottom of the figure.
It is often assumed that the premises network will use the Smart Energy Profile 2.0 (SEP2) for communication and the PEV will be able to use this protocol for communication directly through the EVSE to the Energy Services Interface (ESI). The ESI can be thought of as the gateway between the premises network and the outside systems. This SEP2 assumption may not be true for many premises networks, in which case the EVSE will need to translate messages from the protocol used by the local network into SEP2 used by the PEV. SAE J2847/3 will define the communications between the EVSE and the PEV for those cases where the inverter is on-board the PEV. It is expected that the EVSE to PEV communications would be by power line carrier (PLC) on the control pilot. If the premises network uses SEP2 and the EVSE is not needed to perform protocol translation for the PEV, it may be possible for the PEV to use a wireless link directly to the network.
When the inverter is in the EVSE it will need to directly interact using the network protocol. This could be SEP2, but in many sites could be a different protocol. The use cases in this document and SAE J2847/3 could help with the design of the EVSE communications, but there are other documents such as IEC TR 61850-90-7 that could be directly used by the EVSE manufacturer. An external inverter will need to interact with the battery management system (BMS) of the PEV. This will be like the communications used for fast charging as defined by SAE J2847/2, but the focus will be very different and changes will be required for DER use. For fast charging, the PEV BMS manages the charging current using the data link. For DER use, the inverter will draw from the battery or push into the battery whatever current is needed to perform its DER function. In this case the BMS defines limits for the inverter, but does not manage the inverter power conversion.