ISO 15118-2: Electric vehicle and charging pile communication protocol (V2G PnC + AC/DC)

Summary

ISO 15118-2 is an application layer communication standard between electric vehicles (EV) and charging piles (EVSE). It defines the message sequence, message structure, TLS security layer and EXI (Efficient XML Interchange) encoding method of alternating current (AC) and direct current (DC) charging processes.Its core feature is Plug & Charge (PnC), which allows users to “plug and charge” through the X.509 certificate chain without the need for RFID cards or App authentication.KopherBit provides complete ISO 15118-2 EV side stacking in EVCC, supporting AC, DC, EIM, PnC modes.

Technical Role

ISO 15118-2 specifies application layer protocol between cars and piles, located above the PLC physical layer (HomePlug Green PHY) and IPv6/TCP/TLS transport layer.A complete charging session consists of the following state machine stages:

SLAC (ISO 15118-3) — signal attenuation pairing.
SDP — SECC Discovery Protocol, obtains the SECC IPv6 endpoint.
TCP connection (TLS 1.2/1.3 required for PnC, TLS optional for EIM).
SessionSetup → ServiceDiscovery → ServiceDetail.
Authentication: PaymentServiceSelection → PaymentDetails (PnC) or Authorization (EIM).
ChargeParameterDiscovery — Both parties negotiate maximum voltage/current/timing.
(DC) CableCheck → PreCharge → PowerDelivery → CurrentDemand Loop → WeldingDetection.
(AC) ChargingStatus loop. 9.SessionStop.

ISO 15118-2 PnC relies on a complete certificate chain: OEM Provisioning Certificate → Contract Certificate, issued by the respective Sub-CA and revocation checked via OCSP / CRL.

Architecture

Subsystem	Role
HomePlug Green PHY	PLC physical layer, specified by ISO 15118-3.
IPv6 / DHCP / SDP	Obtain SECC IPv6 link and communication endpoint.
TCP/TLS	Encrypted channel; PnC forces TLS.
V2G Transfer Protocol (V2G TP)	Application layer message packaging and serialization.
EXI Codec	XML messages are encoded and decoded using EXI binary high efficiency.
State Machine	ISO 15118-2 Charging session state machine.
PKI / Crypto	X.509 certificates, ECDSA, TLS handshake, Contract Certificate installation/update.

Key Capabilities

Supports both AC charging (such as home wall-mounted wallbox) and DC fast charging (CCS1 / CCS2 high-voltage DC pile).
PnC (Plug & Charge): Users can complete the authentication by plugging in the gun, no RFID/App is required.
EIM (External Identification Means): Compatible with existing RFID, App, and QR code payment processes.
TLS 1.2/1.3 encryption and mutual authentication (PnC mode).
EXI encoding: Significantly reduces message size and encoding and decoding costs compared to original XML.
Standardized error codes: During the DC charging process, battery overheating, voltage out of range, charger connector lock failure, EVRESS failure, etc. can be reported.

Engineering Inputs Required

Input	Purpose
Charging mode	Support combination of AC, DC, PnC, and EIM.
BMS signal matrix	SoC, target voltage/current, maximum allowable voltage/current, temperature, error code.
PKI Settings	OEM Provisioning CA, Contract CA, Trust Anchors, OCSP Endpoints.
Charging hardware	CCS1 / CCS2 / GB/T corresponding physical connector and PLC module.
Vehicle Network	CAN/CAN FD signal definition between EVCC and BMS and VCU.
Interoperability testing requirements	EVSE brands and market regulations expected to be supported (Europe, North America, China, Japan).

How KopherBit Supports This

EVCC Software stack: KopherV2G provides ISO 15118-2 complete stack: SLAC, SDP, TLS, V2G TP, EXI, state machine.
PnC Integration: Assist customers to import OEM CA, Contract CA, SubCA, OCSP and Contract Certificate installation processes.
AUTOSAR integration: Package the ISO15118 process into a BSW configurable SWC through KopherSAR and KopherConfig to interface with the vehicle BMS and VCU.
Verification: KCU Gen2 Testbench provides interoperability testing and message tracking.

FAQ

What is the difference between ISO 15118-2 and DIN 70121?

DIN 70121 is the German DIN standard before ISO 15118-2, which only covers the basic DC charging process, does not support PnC, and does not force TLS.ISO 15118-2 is an ISO international standard covering AC + DC, adding PnC, encryption and a more complete message set.Most modern CCS charging stations support both and are selected based on vehicle capabilities.

What is the difference between PnC and EIM?

PnC completes identity authentication and billing identification through the X.509 certificate chain. The user can start charging by inserting the gun; EIM still requires external (RFID / App) authentication before charging is allowed.

Does it support two-way charging (V2G / V2H / V2L)?

ISO 15118-2 is one-way charging.Bidirectional charging requires ISO 15118-20.

Is TLS mandatory?

PnC mode must use TLS (1.2 or 1.3); EIM mode can optionally use TLS.

How to obtain and update Contract Certificate?

EV interacts with the back-end Mobility Operator Issuance Center (CPS) through the PnC process to complete the installation or update of the Contract Certificate on the charging pile.KopherBit EVCC supports CertificateInstallation and CertificateUpdate services.

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