Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Use Cases for Wireless Charging Communication for Plug-in Electric Vehicles (SAE J2836/6)
1. Standard Scope and Purpose
SAE J2836/6 is an information report that defines use cases for communication between a plug-in electric vehicle (EV) and the wireless EV supply equipment (WEVSE) for magnetic-field wireless power transfer (MF-WPT) per SAE J2954. It addresses the communications needed to detect the charging system, manage the charging process, and monitor it in real time. The standard also covers communication to the charging infrastructure and power grid for smart charging, aligning with the general framework established in SAE J2836/1 for V2G communications.
The document is part of a coordinated set: SAE J2847/6 specifies the functional messaging required to support these use cases, and SAE J2931/6 defines the protocol profiles for the underlying communication layers. This revision (2021) refines the initial step 1 release and focuses on providing a robust communication framework for residential (home) chargers.
2. Wireless Charging Communication Phases
The use cases follow a stepwise process that mirrors conductive charging but introduces unique steps specific to wireless power transfer. The main phases are:
- Wireless Charging Spot Discovery – detecting the presence of an active WEVSE without physical coupling.
- Service Discovery (Optional) – exchanging capabilities and configuration information between the EV and WEVSE.
- Vehicle Alignment Procedure – guiding the driver or automated system to align the vehicle pad to the ground pad for optimal power transfer efficiency.
- Power Transfer Procedure – initiating, controlling, monitoring, and terminating the wireless energy transfer, including safety interlocks.
The following table summarizes the phases and their key communication requirements:
| Phase | Description | Key Communication Requirements |
|---|---|---|
| Spot Discovery | Near-field or short-range detection of a WEVSE | Reliable detection without false triggers; coexistence with multiple units |
| Service Discovery | Optional exchange of load capacity, pricing, or scheduling info | Compatible message set; security for sensitive data |
| Vehicle Alignment | Precise positioning of the vehicle-side coil relative to ground-side coil | Low-latency feedback; tolerance for misalignment guidance |
| Power Transfer | Active energy transfer with real-time monitoring | Command/response with redundancy; fault detection |
3. Engineering Design Insights and Considerations
The architecture in SAE J2836/6 clearly separates functional and physical elements, emphasizing the division between control and power domains. This design ensures that communication protocols can be developed independently of the specific hardware implementation. A critical aspect is the coexistence of inductive (wireless) and conductive charging systems on the same vehicle—a pragmatic requirement for early adoption.
🛠️ Engineering Insight: The wireless charging process demands tight coordination between alignment and power transfer to maintain high efficiency. J2836/6 defines the use cases that sequence these operations, building directly on the alignment methodology from SAE J2954. Without proper communication handshake steps, efficiency and safety can be compromised.
⚠️ Common Mistake: Directly copying conductive charging communication without accounting for alignment tolerances and variable coupling. Unlike conductive, wireless charging requires additional discovery and adjustment phases to adapt to positioning differences and ensure consistent power delivery.
Frequently Asked Questions
- How does wireless charging spot discovery ensure reliable detection without interference?
- The EV and WEVSE use a dedicated initial communication handshake (often through low-power signaling) to detect presence and confirm compatibility. The protocol includes filtering mechanisms to avoid interference from adjacent units or other wireless systems.
- What are the key performance requirements for the vehicle alignment procedure?
- The alignment feedback must have low latency (typically sub-second) and sufficient precision to guide the vehicle within the tolerance window specified in SAE J2954. This ensures that the coupling coefficient remains high for efficient power transfer.
- How does the system handle coexistence of conductive and wireless charging on the same vehicle?
- The vehicle system must manage both interfaces through a common control architecture—typically the vehicle communication controller (VCC) selects one mode at a time and ensures that conductive and wireless systems do not conflict. J2836/6 explicitly requires that the communication protocol support this dual-mode scenario.
- How do the communication protocols ensure low latency and reliability during power transfer?
- The protocols profiled in SAE J2931/6 are tailored for deterministic timing over appropriate physical layers (e.g., dedicated short-range communication). Messages related to power control are given priority with redundant transmission paths to maintain safety and control loop stability.
