Vehicle to Grid (V2G) Software Stack (ISO/IEC 15118)
The global consumer electric vehicle market is increasing continuously and impressively. V2G-technology for electric charging communication has become a key technology in this market. V2G is providing standardized Plug & Charge features – automated and secured communication between electric vehicles and charging stations. Tamper-free charging and billing is working fully autonomously.
SEVENSTAX V2G is a next level Vehicle-to-Grid communication software stack for embedded systems focusing on an outstanding performance while reducing the memory footprint to a minimum.
We help the world’s leading OEMs and suppliers in the automotive and charging equipment fields with innovative software solutions. Reduce your time to market by developing with our worldwide established, ISO 15118and DIN 70121 conform, SEVENSTAX V2G software stack.
Your Advantages with the Embedded SEVENSTAX V2G Stack
Small memory footprint
- ROM: 129 kB
- RAM: 14 kB
- ROM: 64 kB
- RAM: 27 kB
- ARM Cortex M MCU
- IAR Embedded Workbench Compiler
- Low Optimization
- TLS 1.2 and 1.3 (future proof)
- ISO 15118 compliant cipher suites
- ISO 15118 compliant X.509 v3 certificates
- XML Signatures for Plug & Charge
Fully tested and proven in the field
- According to automotive standards
- MISRA checked
- Automated testing based on SEVENSTAX Test Bench
- AUTOSAR Complex Device Driver (CCD) integration
Vehicle-to-Grid Background Information
Vehicle to Grid (V2G) is a concept about the intelligent, bidirectional transport of energy between an electric vehicle and the power grid, including a communication standard for electric vehicles describing the communication between charging stations (EVSE – Electric Vehicle Supply Equipment) and vehicles (EV).
The standard is specified by the ISO/IEC 15118 / SAE J2847-2, as well as DIN 70121, which is an early component of the ISO/IEC 15118 and exclusively describes direct current charging.
Currently, the V2G communication takes place via Power-line Communication (PLC) according to the HomePlug Green PHY (HPGP) standard (also compare SAE J2931/4 and ISO15118-3). HPGP could be considered a subset of the prominent HomePlug AV (HPAV), therefore HPAV devices are compatible with HPGP. However HPGP was extended with a few features concerning E-Mobility applications and Smart Metering. Physically, PLC takes place via one of the two electrical lines not used for the charging current of the CCS (Combined Charging System) plug, called the control pilot. However, for this scenario the line coupling of the PLC module must be properly equipped for this task (transmitter, no zero crossover recognition, etc.). Apart from the PLC communication, a rudimentary communication via PWM signal is always taking place on the control pilot. Via the duty cycle it is possible to signal various charging parameters without utilising PLC. If the duty cycle is maintained at 5%, the V2G communication can potentially be initiated (always initiated by the vehicle).
Since as a matter of principle, PLC can include crosstalk of different networks. But it needs to be ensured that the EV is communicating exclusively with the EVSE it is directly connected to. In order to achieve this, Signal Level Attenuation Characterization (SLAC) is used. In brief, when SLAC takes place, the PLC driver of the EV sends a message via broadcast to all PLC devices “nearby”. All EVSE PLC interfaces, that receive this package respond and include the signal strength of the former request into the response as payload. The EV side then chooses the correct EVSE by using the one with the highest signal strength.
After identifying the right EVSE the communication will be initiated by the EV based on IPv6. At the start of the process the IP-address of the EVSE is determined with the use of the SECC Discovery Protocol (SDP) and thereafter the proper TCP based V2G connection is established. Additionally, the connection can be secured utilising Transport Layer Security (TLS).
Two different scenarios for the payment process have been taken into consideration in the V2G communication. When using “External Identification Mean (EIM)” the payment process takes places independently from the charging communication e.g. via credit card at the charging station terminal. Also, the secure transmission of billing information via the communication interface, allows a fully automated payment process: Plug and Charge. As a requirement, the connection has to be secured by TLS. The authentications take place via X.509 certificate and V2G messages are signed. An according certificate infrastructure – Public Key Infrastructure (PKI) is required.
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