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SAE J3068/2: Control of Bidirectional Power for AC Conductive Charging
As electric vehicles become integral to energy systems, the ability to manage bidirectional power flow between the vehicle and the grid is essential. SAE J3068/2, released in January 2024, defines a new Protocol Version for AC conductive charging that enables four-quadrant power transfer while conforming to SAE J3072 and IEEE 1547. This standard unlocks advanced vehicle-to-grid (V2G) capabilities, allowing control of both real and reactive power during charging and discharging to support site electrical limits and grid management.
Understanding SAE J3068/2 and Its Role in Bidirectional Charging
SAE J3068/2 extends the existing J3068 standard by introducing a dedicated Protocol Version (number 252) that defines the signals and logical rules necessary for bidirectional operation. The standard specifies requirements for both electric vehicle supply equipment (EVSE) and electric vehicle (EV) components. A key aspect is its alignment with SAE J3072 (interconnection requirements for utility-interactive inverters) and IEEE 1547 (standard for interconnection of distributed energy resources). This ensures that vehicles used as grid resources meet consistent safety and performance standards.
Protocol Version 252 and LIN Communication
At the core of J3068/2 is the use of a Local Interconnect Network (LIN) for communication between the EV and EVSE. The standard defines over a dozen LIN signals specifically for bidirectional power control. These signals handle authorization, mode selection, target setting, and status reporting.
| LIN Signal | Function |
|---|---|
| EvPwrCtrlModesAvail | Signals which power control modes are available from the EV |
| SePwrCtrlAuth | Provides authorization from EVSE for specific power operations |
| SeTargets1ElementX | Conveys target real and reactive power values |
| EvGridCodeStatus | Reports grid code compliance status |
| SePwrCtrlMode | Selects the active power control mode |
Each signal is encoded in a specific LIN frame with defined schedules. The protocol ensures deterministic behavior, making it suitable for power control applications.
Power Control Modes: Grid-Following vs. Grid-Forming
J3068/2 supports two primary operational modes: Area EPS Following and Local EPS Forming. In Area EPS Following mode, the EV acts as a current source synchronized to the utility grid, managing charge and discharge according to external setpoints. In Local EPS Forming mode, the EV can operate as a voltage source in an islanded microgrid, enabling power backup and local grid support. Both modes require proper authorization and real-time communication via LIN signals.
🛠️ Engineering Design Insight: J3068/2’s dual-mode architecture allows the EV to transition seamlessly between grid support and standalone operation. The LIN protocol provides the low-latency control loop necessary for stable power regulation in both scenarios.
Safety is paramount when exporting energy to the grid. The standard mandates that devices conform to the latest editions of SAE J3072 and IEEE 1547, which include anti-islanding detection, voltage/frequency regulation, and utility disconnect requirements.
⚠️ Common Implementation Mistake: A frequent error is neglecting to properly configure the Protocol Version number to 252. Using an older version may cause interoperability failures or unsafe operation.
Frequently Asked Questions
How does Protocol Version 252 enable bidirectional power flow?
Protocol Version 252 introduces new LIN signals and state machines specifically for controlling real and reactive power in both directions. These signals communicate availability, authorization, and setpoints, allowing the EV to both draw from and supply power to the grid.
What are the key LIN signals used for power control?
Key signals include EvPwrCtrlModesAvail, SePwrCtrlAuth, SeTargets1ElementX, SePwrCtrlMode, and EvGridCodeStatus. These handle mode negotiation, authorization, and target value exchange.
How are safety requirements addressed for discharging to the grid?
Safety is enforced through conformance to SAE J3072 and IEEE 1547, which require grid disconnect, anti-islanding, and power quality protections. The LIN protocol also ensures secure communication and state validation.
How does J3068/2 coordinate with SAE J3072 and IEEE 1547?
J3068/2 explicitly requires compliance with both standards for any device supporting bidirectional operation. This includes EVSE and EV inverters meeting the interconnection and inverter requirements of those documents, ensuring a unified approach to grid integration.
