Implementing Interoperable V2G-AC
One Grid Interface, Two Certified Devices
In V2G-AC, the grid support technology is in the car, but the grid interface is the EVSE. The EV’s onboard bidirectional inverter converts the grid AC energy to battery DC stored energy and in reverse, to grid-ready AC sent to the charger it plugs into — the EVSE. However, from a utility perspective, the EVSE is accountable for insuring grid safety and supervises the export rather than performing it. Without standards V2G-AC could not move forward: the grid code, the onboard inverter, and the communications tying them together sit in different but connected systems and two critical standards were just published this year.
2026 closed the loop for North American standards. UL 1741 SC published in May (the standard for V2G-AC EVSEs); ISO 15118-20 Amendment 1 followed in July which is triggering an update to the SAE J3072 standard for the V2G-AC EV. With both now in print, interoperable V2G-AC can move to the certification program stage — one that spans two devices, so getting to market means certifying both the EV and the EVSE independently, and proving the communications link that binds them into a single grid resource that works as required.
The US path: independent certifications on the EV and the EVSE
In North America, the grid-code functions IEEE 1547 defines — ride-through, power controls, anti-islanding, response curves — run on the EV’s onboard inverter. SAE J3072, last updated in 2024, specifies the onboard inverter requirements, requires conformance to IEEE 1547-2018, and defines the accompanying EVSE–EV communications. With the publication of ISO 15118-20 Am 1, it is being updated to recognize ISO 15118 as a valid J3072 communications protocol.
The EV and the EVSE are certified independently: J3072 applies to the EV, and UL 1741 SC applies to the EVSE. SC creates a new certification category for the bidirectional AC charger. Under SC, the charger is the interconnection point and the oversight supervisor: it authorizes the vehicle to discharge based on the vehicle’s J3072 certification, duplicates the IEEE 1547 ride-through, under and over voltage and frequency trip, and enter-service requirements on the export it supervises, and opens its contactor if the EV discharges when not authorized.
The goal of UL 1741 SC is to manage the export of power and energy from a grid support EV while mimicking key grid safety functions. The expectation is that the J3072 EV will perform all of the IEEE 1547 grid functions as required, BUT, because this is new technology and the utilities don’t have experience with EV OEMs as DER vendors, the certified UL 1741 SC EVSE is designed to duplicate a small, but critical set of responses to anomalous grid conditions, regardless of the EV response.
UL 1741 SB CRD: Certifying a combination of an EVSE and EV
An alternative route is the UL 1741 CRD for DER systems, which certifies a matched EV-and-EVSE combination as a single DER — but then only that specific matched pairing can interconnect and deliver V2G. Independent certification is what makes V2G-AC interoperable: any certified vehicle, any certified charger can work together to supply V2G services to the grid.
This is an attractive alternative to OEMs with their own V2G EVs and EVSEs and a reasonable market share. The CRD can also be an interim step toward full UL 1741 SC and/or J3072 certification. An early design decision to follow both standards, even with a CRD objective, means that evolving to UL 1741 SC and J3072 independent certifications and products.
Of note is that the “certification” requirement of a J3072 EV is still being debated. J3072 itself essentially allows an OEM to self-certify a J3072 EV while utilities strongly prefer independent certification through 3rd party labs authorized to do the certification in question. It remains to be seen how the utilities and OEMs settle this issue.
The same issue does not exist for Ac EVSEs. There is not any sort of “escape hatch” that allows EVSE OEMs to self-certify.
V2G-AC upstream communications standards are messy
One of the nuances of V2G is that the DER – either the EVSE in V2G-DC or EVSE/EV combination in V2G-AC – must communicate “upstream” from the EVSE to grid operator through some sort of aggregation platform, most likely a CMS (Charge Management System operated by a CPO – Charge Point Operator).
In the US, those upstream communications are standardized in IEEE 1547 and include IEEE 2030.5, SunSpec Modbus or IP and IEEE 1815 (DNP3). All three protocols support grid code messages for managing DERs. However, these protocols are not designed to managing a charging station infrastructure. The industry has adopted the Open Charge Point Protocol (OCPP) for managing a fleet of charging stations. But OCPP was not designed to support grid support inverters and only just recently added that support in version 2.1.
And another HOWEVER is that OCPP is not recognized as an interoperability protocol in IEEE 1547. So, the North American V2G-AC standardization landscape is further complicated by the inconsistent standards that apply. Our expectation is that the industry will move towards using OCPP 2.1 for V2G-AC simply because of the investment by EVSE and CMS OEMs in this standard.
BUT (one more wrinkle) the upstream and downstream communications protocols are also inconsistent in North America: J3072 protocols do include IEEE 2030.5 and SunSpec ModBus but the EV domain has invested in ISO 15118 to manage the EV-EVSE interface and ISO 15118-20 Am 1 is the answer to V2G-AC for that interface.
As should be painfully apparent, interoperability for V2G-AC has significant protocol challenges to overcome.
The EU path: a different split, being codified now
In the EU, a different division of grid-code and communication functions between the EV and the EVSE is being codified in a set of updated standards, under the EN 50549 grid code plus country codes and driven by the pending RfG (Request for Generators) 2.0 revision of the EU interconnection regulation. The package mirrors the US structure with different documents: ISO 5474-2 Ed 2 covers the onboard inverter (the closest counterpart to J3072), IEC 61851-1 Ed 4 covers the EVSE (the EU counterpart to UL 1741 SC), and the EU version of ISO 15118-20 Amendment 1 adds the EV–EVSE communications to support V2G-AC. Each component will be independently tested and certified for both grid-code and communications compliance, with certifications starting soon after the new standards are published.
Until the package lands, national paths do the work. Germany’s VDE 4105 today certifies the complete functional system — vehicle model plus cable plus wallbox — as one unit; the pairing does not extend to a different wallbox (similar to UL 1741 SB CRD). That is the pairwise constraint the new standards are written to remove. And as with every grid code: a product certified for one market is not compliant in another.
ISO 15118-20 did not cover V2G-AC — Amendment 1 does
ISO 15118-20 introduced bidirectional power transfer at the connector, and in V2G-DC that is enough, because the charging station is the DER and carries the grid-code certification itself. V2G-AC needs more: the utility’s IEEE 1547 settings have to reach an inverter riding in the car, and as published in 2022, ISO 15118-20 carried none of the IEEE 1547 grid-support functions — true of OCPP 2.0.1 as well, in the US and the EU alike. That gap is why SAE developed J3072 with communications protocols IEEE 2030.5 or SunSpec Modbus, and why UL developed 1741 SC.
Amendment 1, published July 13, 2026, closes the gap. It adds AC DER services to ISO 15118-20: AC_DER_SAE, aligned to SAE J3072 and IEEE 1547, and AC_DER_IEC, built on IEC 61851-1 Ed 4. The two regional versions have different protocol behaviors. And the scoping point survives the amendment: ISO 15118-20 carries the communication functions, not the grid code. Certifying the protocol proves nothing about the inverter’s ride-through response. V2G-AC requires both proofs.
Why V2G-AC is harder to test than V2G-DC
In V2G-DC the device under test is one box. V2G-AC spreads the proof across a two-device system:
- Two devices, two certifications, one grid resource. The EV and EVSE certify independently, but the certifications only mean something when the pair can connect, interoperate and perform as a single DER.
- The handshake is part of the certification. Testing has to drive the J3072 authorization-to-discharge exchange, including the failure path where the EVSE opens its contactor on unauthorized export. UL 1741 SC requires certification of the J3072 protocol implementation is there is an industry program in place.
- Upstream settings flow through the charger. IEEE 1547 interoperability testing verifies that utility settings sent downstream arrive through the EVSE onto the EV and take effect — a communications proof layered on a power proof. This is effectively validation that the translation from upstream to downstream communications protocols works correctly.
- Simulating a UL 1741 SC or a J3072 EV are part of the certification process. Certifying a DC EVSE requires simulating grid conditions and capturing and analyzing the EVSE power behaviors. The EV can be simulated as simply a battery or a DC power source. For AC, certifying a J3072 EV requires simulating the EVSE and certifying a UL 1741 SC EV requires simulating a J3072 EV. Not only are these added complexities but these systems do not yet exist commercially.
- The anchor standards just published. UL 1741 SC in May 2026 and ISO 15118-20 Amd 1 in July 2026: test programs are standing up against freshly printed targets, with US and EU variants (not yet published) that differ.
How QualityLogic tests and certifies V2G-AC
QualityLogic built the first automated certification test product for UL 1741 SB testing. It supports the DER protocols IEEE 1547 requires — IEEE 2030.5, SunSpec Modbus, and IEEE 1815.2 — and drives the full grid-code sequence end to end. QualityLogic’s automation has taken grid-code certifications for the firmware and protocol aspects from 4-5 weeks of manual effort down to as little as 32 hours.
The same framework is applicable to both V2G topologies — the UL 1741 SB test system is already in use for V2G-DC EVSEs For V2G-AC we are working with EV/EVSE simulator system partners to develop the required J3072 and UL 1741 SC simulation systems for certification testing. QualityLogic already equips with the major NRTLs with its tools for protocol and UL 1741 SB certifications, so extending into V2G-AC certification testing is a logical evolution of both tools and the relationships for both the North American and European paths.
********
