ISO 15118

What is ISO 15118?

ISO 15118 is an international communication standard for electric vehicles developed by the International Organization for Standardization (ISO) to establish a common communication protocol for electric vehicles (EVs), charge points (CPs), and charge point management systems (CPMSs). ISO 15118 specifies a secure and reliable way for these devices to exchange authentication and authorization data, charging parameters, and billing information.

What are the key components of ISO 15118?

ISO 15118 relies on two core controllers to manage communication between the vehicle and the charging station:

Key components and requirements

• EVCC (Electric Vehicle Communication Controller): The controller within the EV that handles the communication.
• SECC (Supply Equipment Communication Controller): The controller within the charging station that handles communication.
• Protocol: Uses Internet Protocol-based communication over the charging cable or wirelessly.
• Versions: Has been updated over time, with major versions including -2 (2014) and -20.

How does ISO 15118 work? 

ISO 15118 defines the communication interface between an electric vehicle and a charging station. It replaces basic analog signaling with an IP-based connection that enables encrypted, bidirectional data exchange between the two endpoints.

When a vehicle connects to a compatible charger, the protocol initiates a structured session: the EV provides vehicle and payment authorisation data, while the charging station requests and validates it before commencing the session. The two parties then align on charge parameters based on battery state and grid conditions, and power delivery begins. All communication is encrypted using TLS, ensuring billing data and user information remain secure throughout.

What are the key use cases and functions of ISO 15118?

When an EV plugs into a compatible charging station, the two devices open an encrypted communication session. The EV shares its identity and charging requirements; the charging station validates them against the backend system and, once authorised, agrees on a charging schedule. This exchange underpins everything from frictionless authentication to real-time grid interaction.

Core functions:

• Authentication and authorization: Enables secure identification of the driver and vehicle before a session begins.
• Plug & Charge: Allows a car to be identified, authorised, and charged automatically upon connection, using digital certificates managed through a Public Key Infrastructure.
• Smart charging: Optimises charging speed and timing based on electricity tariffs, grid load, and the driver’s departure needs.
• Vehicle-to-grid (V2G): Supports bidirectional power flow, allowing vehicles to both draw from and supply power back to the grid.

Core use cases

Authentication, Authorization, and Plug & Charge

ISO 15118-enabled charge points (CPs) allow charge point operators (CPOs) to provide EV drivers with a more seamless and secure charging experience. The protocol makes this possible by establishing a reliable communication environment between the EV, the CP, and the charge point management system (CPMS)—a centralized backend software for managing chargers and charging networks.

In the typical scenario, EV drivers can initiate charging only after authenticating themselves and their car. Upon authenticating through an app, RFID card, or another method, the backend system authorizes or disallows charging depending on preset criteria. 

The purpose of this data exchange is for the CPMS to know who’s the driver charging which car, whether the driver is allowed to use this particular charger, and who needs to receive the bill for the session. While authentication and authorization happen in a matter of seconds, the need for drivers to physically authenticate is an added inconvenience.

ISO 15118 makes this process more accessible thanks to the Plug & Charge functionality. As the name implies, with Plug & Charge, EV drivers can simply plug into a CP, and authorization and authentication happen automatically. This works because after initial set-up, the EV stores information about the driver, which is then automatically shared with the CP so charging can begin immediately. 

To put it simply, a Public Key Infrastructure system manages the information exchange. This secure public-key management system uses hardware, software, and procedural units to acquire, store, and manage sensitive data.

Smart Charging

ISO 15118 enables smart charging by establishing two-way communication between the EV and charge point to set charging speeds and schedules. The EV sends data about how much electricity it needs and by what time. The charge point then calculates how much energy it needs to deliver to efficiently meet the required time and state of charge (SOC) — optimising for factors like electricity tariffs and grid load.

Vehicle-to-Grid (V2G)

ISO 15118 also enables vehicle-to-grid (V2G), which allows bidirectional energy exchange between the grid and compatible EVs. Normally, electricity flows in one direction — from the grid to the charger to the EV. V2G reverses that flow, allowing EVs to send energy stored in their batteries back to the charging station and the grid.

This capability helps the grid handle periods of high demand without activating peak generation sources such as coal plants, and allows EV batteries to act as distributed storage for excess renewable energy. ISO 15118-20 introduced formal V2G support through Bidirectional Power Transfer (BPT), available for both AC and DC charging.

Initiating a V2G session involves four key steps:

Step 1: Check for available charging services

The EV sends a ServiceDiscovery request to the charging station to find out which charging services it offers — AC, DC, wireless power transfer (WPT), or automatic connection device (ACD). If BPT is available, the EV can select it to enable both charging and discharging during the session.

Step 2: Mutually exchange charging limits 

The EV and charging station exchange their technical limits for bidirectional power flow via a ChargeParameterDiscovery message pair. The EV communicates its minimum and maximum power and current limits for both charging and discharging, as well as its target energy request, maximum energy needed for a full charge, and the minimum energy it needs immediately. The charging station responds with its available current, nominal voltage, and grid frequency. This mutual exchange ensures both parties operate within safe and compatible parameters.

Step 3: Calculate and send a power profile to the charging station

Using the exchanged limits, the EV calculates a power profile — an ordered sequence of time and power value entries that together form a curve illustrating planned charging and discharging over time. Positive values indicate charging periods; negative values indicate discharging. This allows the charging station to plan ahead for how much power it needs to provide or absorb at each point during the session.

Step 4: Control the charging process in the charging loop

Once power flow begins, the EV and charging station continuously exchange bidirectional control messages. The EV reports its present active and reactive power, while the charging station provides set-points for target frequency, active power, and reactive power. This ongoing communication allows the charging station to react to real-time grid conditions and request ancillary services from the EV as needed — ensuring the EV behaves as a grid-friendly distributed energy resource throughout the session.

Data security

Data security is an essential consideration in EV charging. Data exchange is protected within the EV ecosystem by using cryptographic layers added on top of hardware and software solutions. ISO 15118, on the other hand, has built-in security measures, meaning that ad-hoc data security is unnecessary when using this protocol. It handles data protection on several levels—through authentication, authorization, and data encryption.

Why is ISO 15118 important for EV adoption?

ISO 15118 is among the important standards for the ongoing development of the EV charging industry. This communication protocol is a secure, reliable, and internationally recognized instrument compatible with many EV hardware and software solutions and charging speeds. Adding to that is the role this protocol will play as grid-balancing technologies become more widespread.

Practical examples of ISO 15118

Here are some practical examples of how ISO 15118 can be used:

• An EV arrives at a public charging station. The EV and the charging station communicate using ISO 15118. The EV sends the charging station its SOC, which is the percentage of battery power that is remaining. 

The charging station also communicates with a back-end system, which manages the charging infrastructure. The back-end system considers the current grid load and sets the optimal charging rate for the EV.

Based on this information, the charging station and the EV agree on a charging schedule. The charging station may start charging the EV immediately or delay it until the grid is under less utilization. The EV and the charging station continue to communicate throughout the charging process. This allows them to adjust the charging rate as needed, for example, if the grid load changes or the EV’s SOC reaches a certain level.

• Let’s continue the previous example, but look at what happens with Plug & Charge. The EV plugs into the charging station. 

The EV and the charging station communicate using ISO 15118. The EV sends the charging station its identity data for authorization. The charging station verifies the EV’s identity and approves it for charging. The charging station initiates the charging session without any user interaction. 

For this process to work, the EV driver needs to go through an initial set-up process, providing their personal and billing information. This information will then be used for each Plug & Charge-enabled session.

• Regarding V2G, energy providers can improve their electricity rates by using the battery capacity of EVs during periods of high demand instead of relying on additional energy sources. In certain instances, utility companies may even pay users for participating in V2G events. For example, when EV drivers supply electricity to the grid during peak demand or charge their vehicles during low energy demand.

Additional Information for ISO 15118

• ISO 15118 is developed by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). This means that the protocol is backed by the expertise of two of the world’s leading standards organizations.
• Because of its scalability and high potential for future growth, EV software and hardware providers are thus interested in making their solutions ISO 15118-compliant.
• The latest version of ISO 15118 is ISO 15118-20. This version includes several improvements, such as V2G support, improved security, and better interoperability.