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Get to know one of the world’s leading international electric vehicle standards
The official nomenclature for ISO 15118 is “Road Vehicles – Vehicle to grid communication interface.” I may be slightly biased, as I’m one of the co-authors of this international standard, but I truly believe that ISO 15118 is one of the most important and future-proof standards available today.
The smart charging mechanism built into ISO 15118 makes it possible to perfectly match the grid’s capacity with the energy demand for the growing number of EVs that connect to the electrical grid. ISO 15118 also enables bidirectional energy transfer in order to realise vehicle-to-grid applications by feeding energy from the EV back to the grid when needed. ISO 15118 allows for more grid-friendly, secure, and convenient charging of EVs.
In this article, we’ll go through the main characteristics of ISO 15118 and each part of the ISO 15118 document family. Let’s start with the story behind the creation of this standard.
In 2010, the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC) joined forces to create the ISO/IEC 15118 Joint Working Group. For the first time, experts from the automotive industry and the utility industry worked together to develop an international communication standard for charging EVs. The Joint Working Group succeeded in creating a widely adopted solution that is now the leading standard in major regions across the globe like Europe, the U.S., Central/South America, and South Korea. ISO 15118 is also rapidly picking up adoption in India and Australia. A note on the format: ISO took over publishing of the standard and it is now known as simply ISO 15118.
ISO 15118 enables the integration of EVs into the smart grid (aka vehicle-2-grid or vehicle-to-grid). A smart grid is an electrical grid that interconnects energy producers, consumers, and grid components like transformers by means of information and communication technology, as illustrated in the image below.
ISO 15118 allows the EV and charging station to dynamically exchange information based on which a proper charging schedule can be (re-)negotiated. It’s important to make sure electric vehicles operate in a grid-friendly manner. In this case, “grid friendly” means that the device supports the charging of multiple vehicles at once while preventing the grid from overload. Smart charging applications will calculate an individual charging schedule for each EV by using the information available about the state of the electrical grid, the energy demand of each EV, and the mobility needs of each driver (departure time and driving range).
This way, each charging session will perfectly match the capacity of the grid to the electricity demand of simultaneously charging EVs. Charging in times of high availability of renewable energy and/or in times where the overall electricity usage is low is one of the main use cases that can be realised with ISO 15118.
The electrical grid is a critical infrastructure that needs to be defended against potential attacks and the driver needs to be properly billed for the energy that was delivered to the EV. Without secure communication between EVs and charging stations, malicious third parties can intercept and modify messages and tamper with billing information. This is why ISO 15118 comes with a feature called Plug & Charge. Plug & Charge deploys several cryptographic mechanisms to secure this communication and guarantee the confidentiality, integrity, and authenticity of all exchanged data
ISO 15118’s Plug & Charge feature also enables the EV to automatically identify itself to the charging station and get authorised access to the energy it needs to recharge its battery. This is all based on the digital certificates and public-key infrastructures made available through the Plug & Charge feature. The best part? The driver doesn’t need to do anything beyond plug the charging cable into the vehicle and the charging station (during wired charging) or park above a ground pad (during wireless charging). The act of entering a credit card, opening an app to scan a QR code, or finding that easy-to-lose RFID card is a thing of the past with this technology.
ISO 15118 will significantly affect the future of global electric vehicle charging because of these three key factors:
With those fundamental elements in mind, let’s get into the nuts and bolts of the standard.
The standard itself, called "Road vehicles – Vehicle to grid communication interface", consists of eight parts. A hyphen or dash and a number denote the respective part. ISO 15118-1 refers to part one and so on.
In the image below, you can see how each part of ISO 15118 is related to one or more of the seven layers of communication that define how information is processed in a telecommunications network. When the EV is plugged into a charging station, the communication controller of the EV (called the EVCC) and the charging station’s communication controller (the SECC) establish a communication network. The goal of this network is to exchange messages and to initiate a charging session. Both the EVCC and SECC must provide those seven functional layers (as outlined in the well-established ISO/OSI communication stack) in order to process the information they both send and receive. Each layer builds upon the functionality that is provided by the underlying layer, starting with the application layer at the top and all the way down to the physical layer.
For example: The physical and data link layer specify how the EV and charging station can exchange messages using either a charging cable (power line communication via a Home Plug Green PHY modem as described in ISO 15118-3) or a Wi-Fi connection (IEEE 802.11n as referenced by ISO 15118-8) as a physical medium. Once the data link is properly set up, the network and transport layer above can rely on it to establish what is called a TCP/IP connection to properly route the messages from the EVCC to the SECC (and back). The application layer on top uses the established communication path to exchange any use case related message, be it for AC charging, DC charging, or wireless charging.
When discussing ISO 15118 as a whole, this encompasses a set of standards within this one overarching title. The standards themselves are broken into parts. Each part undergoes a set of predefined stages before being published as an international standard (IS). This is why you can find information about each part’s individual “status” in the sections below. The status reflects the publication date of the IS, which is the final stage on the timeline of ISO standardisation projects.
Let’s dive into each of the document parts individually.
The figure above outlines the timeline of a standardisation process within ISO. The process is initiated with a New Work Item Proposal (NWIP or NP) which enters into the stage of a Committee Draft (CD) after a time period of 12 months. As soon as the CD is available (only to the technical experts who are members of the standardization body), a balloting phase of three months starts during which these experts can provide editorial and technical comments. As soon as the commenting phase is finished, the collected comments are resolved in online web conferences and face-to-face meetings.
As a result of this collaborative work, a Draft for International Standard (DIS) is then drafted and published. The Joint Working Group may decide to draft a second CD in case the experts feel that the document is not yet ready for to be considered as a DIS. A DIS is the first document to be made publicly available and can be purchased online. Another commenting and balloting phase will be conducted after the DIS has been released, similar to the process for the CD stage.
The last stage prior to the International Standard (IS) is the Final Draft for International Standard (FDIS). This is an optional stage which can be skipped if the group of experts working on this standard feel that the document has reached a sufficient level of quality. The FDIS is a document that does not allow for any additional technical changes. Therefore, only editorial comments are allowed during this commenting phase. As you can see from the figure, an ISO standardisation process can range from 24 up to 48 months in total.
In the case of ISO 15118-2, the standard has taken shape over four years and will continue to be refined as needed (see ISO 15118-20). This process ensures that it remains up-to-date and adapts to the many unique use cases around the world.
Sara stands for Station Analytics and Remote Administration
The Open Charge Alliance is the official body that specifies OCPP 2.0.1 and defines a set of certification profiles. Each profile tests a certain set of functionalities. Depending on the functionality of your charger or CSMS, you might want to certify for either a subset or all of these profiles.
Continuous Integration / Continuous Deployment (CI/CD)
Scotti stands for Simple Compliance Testing Tool for Interoperability.
Efficient XML Interchange (EXI) is a very compact representation of XML. All ISO 15118 messages are defined in XML. EXI improves serialisation and parsing speed on embedded devices (like an EV and a charging station controller) and allows more efficient use of memory and battery life, compared to standard (textual) XML.
The Message Queuing Telemetry Transport (MQTT) is a lightweight, publish-subscribe network protocol that transports messages between devices.
A Charging Station Management System (CSMS) helps you monitor, maintain, and control your charger network.
Automated Connection Device (ACD), a conductive charging concept that doesn't require a person to plug in the charging cable. A first implementation is ACD-P, where 'P' stands for 'pantograph' charging of buses.
Power line communication, a communication technology that enables sending data over existing power cables.
Signal Level Attenuation Characterisation (SLAC) is based on power line communication (specifically HomePlug Green PHY) and is a protocol to establish the data link between the EV and the charging station via the charging cable.
Charge Point Operator, the entity monitoring and managing an EV charger network.