There are multiple challenges associated with vehicle-to-grid (V2G) systems. Of course, they must interface efficiently and safely between the vehicle and the grid without interfering with the grid’s operation. They’re also expected to meet multiple standards for distributed energy resources (DERs), including control and communications protocols.
There are three V2G architectures — V2G-dc, V2G-ac, and V2G-Split inverter — each with unique challenges.
The principal elements of V2G installations are a bidirectional onboard battery charger (BOBC), a bidirectional, four-quadrant (4Q), inverter, and a smart inverter control unit (SMCU). The SMCU includes grid support and communications functions, which are not required for basic EV charging.
The difference between the three V2G architectures is where the bidirectional power conversion and the SMCU smart functions are placed (Figure 1):
- V2G-dc – The BOBC is in the EV, and a 4Q inverter and SMCU are collocated in the electric vehicle supply equipment (EVSE)
- V2G-ac – The BOBC, 4Q inverter, and SMCU are collocated in the EV
- V2G-Split Inverter – The BOBC and 4Q inverter are in the EV, and the SMCU is in the EVSE
Figure 1. A block diagram of the three basic V2G architectures. (Image: Interstate Renewable Energy Council)
SMCU and system integration testing
Testing the BOBCs and 4Q inverters in V2G systems is like testing conventional battery chargers and inverters with the added complexity of bidirectional operation. The challenges when testing V2G systems relate to SMCU and system integration testing.
Interconnecting a V2G-enabled EV as a DER on the utility grid is a complex process. There are multiple standards to consider, and the implementation depends on the V2G architecture being deployed. Some of the standards that must be satisfied include:
North America
SAE J3072 Interconnection Requirements for Onboard, Utility Interactive, Inverter Systems, includes onboard grid-interactive inverter requirements. It incorporates IEEE 1547-2018, IEEE 1547.1, and IEEE 2030.5.
- IEEE 1547.1-2020 is the standard for conformance test procedures and equipment interconnecting DER with electric power systems and associated interfaces.
- IEEE 1547-2018 is the standard for interconnection and interoperability of DER with associated electric power systems interfaces and mandatory support functions.
- IEEE 2030.5 is a secure and scalable application-layer protocol built upon standard Internet protocols. The standard contains DER models based on IEC 61850.
Europe
Open Charge Point Protocol (OCPP) is the open-source communication standard for EV charging stations and network software companies.
- IEC 63110-1:2022 is a protocol for managing EV and EVSE charging and discharging.
The three cases associated with V2G system architectures include:
V2G-dc, where the BOBC is in the EV, and the 4Q inverter and SMCU are in the EVSE. Testing must ensure that the EVSE can meet the standards for grid connectivity, including coordinating the interaction of the BOBC and the 4Q inverter with one another and the grid, as well as the SMCU’s ability to support external communications.
V2G-ac, where the BOBC, the 4Q inverter, and SMCU are in the EV, must meet grid connectivity requirements. In addition to functional testing of the system elements in the EV, testing must confirm the EVSE functions correctly as the intermediary coordinating connectivity and communications between the EV and the grid.
V2G-Split Inverter (also called Split Ac-V2G), where the BOBC and 4Q inverter are in the EV and the SMCU is in the EVSE, and testing must ensure that the combined system meets the grid connectivity and communications requirements.
The EVSE is the ultimate arbiter between the V2G system and the grid in each case. Testing is needed to ensure it effectively connects with external systems like a utility-led distributed energy resource management system (DERMS). In other cases, it must communicate with third-party systems like a charge network operator (CNO) that manages a fleet of EVSEs.
There are different types of CNOs with different communication and control needs, such as fleet operations, apartment buildings, commercial locations like shopping centers and parking lots, and so on. In this case, communication from the utility DERMS comes through the CNO that manages EVs’ actual charging and discharging and communicates power flow requirements with individual EVSEs (Figure 2).
Figure 2. The testing and certification requirements of the three V2G architectures. (Image: Keysight)
Summary
The challenges associated with simulating and testing V2G modules lie mainly in system integration and communications. The specific challenges vary depending on the V2G architecture, such as V2G-dc, V2G-ac, or Split Inverter V2G.
References
- Battery simulation and testing of V2G modules, Rexgear
- Communications Protocols for Grid-EV Integration, Quality Logic
- Comprehensive Assessment of On-and Off-Board V2G Technology Performance on Battery and the Grid, Electric Power Research Institute
- Electric Vehicle-to-Grid (V2G) Technologies: Impact on the Power Grid and Battery, MDPI sustainability
- Electric Vehicles As Distributed Energy Resources, Keysight
- Vehicle-to-grid (V2G) standards for electric vehicles, Interstate Renewable Energy Council
Images
- Figure 1, Interstate Renewable Energy Council, Page 6, Figure 1
- Figure 2, Keysight, Page 15, Figure 4
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Filed Under: FAQs, Testing and Safety, Vehicle-to-Grid (V2G)