What is ISO 15118? – V2G Clarity

What Is ISO 15118?

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. 

In a nutshell, ISO 15118 is an international standard that outlines the digital communication protocol that an electric vehicle (EV) and charging station should use to recharge the EV’s high-voltage battery. As part of the Combined Charging System (CCS), ISO 15118 covers all charging-related use cases across the globe. This includes wired (AC and DC) and wireless charging applications and the pantographs that are used to charge larger vehicles like buses.

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 realize 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. You’ll walk away with an understanding of the following themes:

History of ISO 15118 

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.  

Vehicle-to-Grid — Integrating EVs into the Grid

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 realized with ISO 15118.
Illustration of an interconnected smart grid

Secure Communications Powered by
Plug & Charge

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 dataC

User-Convenience as a Key to a 
Seamless Charging Experience

ISO 15118’s Plug & Charge feature also enables the EV to automatically identify itself to the charging station and get authorized 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:
 
  1. Convenience to the customer that comes with Plug & Charge
  2. The enhanced data security that comes with the cryptographic mechanisms defined in ISO 15118
  3. Grid-friendly smart charging 
With those fundamental elements in mind, let’s get into the nuts and bolts of the standard.  

The ISO 15118 Document Family

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 (powerline communication via a HomePlug 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.

The eight parts of ISO 15118 and their relation to the seven ISO/OSI layers

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 standardization projects

Let’s dive into each of the document parts individually.

Part 1 is called “General information and use-case definition” and is known as ISO 15118-1. It outlines the intention of the standard and explains its overall goals by defining terms and use cases. Here are some of the use cases described in ISO 15118-1. Certain use cases are only described in the second edition (Ed. 2) of ISO 15118-1.

  • Automated identification and authorization via Plug & Charge
  • Manual identification and authorization (e.g. via RFID card or QR code)
  • Wired charging—both alternating and direct current  
  • Wireless charging (Ed. 2)
  • Bidirectional power transfer, which allows the EV to provide energy to the grid (Ed. 2)
  • Charging buses via pantographs (Ed. 2)
  • Load management (smart charging) for all charging modes
  • Renegotiation of charging schedules while charging to react upon unforeseen changes in the grid
  • Value-added services that allow additional information to be exchanged via separate communication channels such as HTTP, HTTPS, FTP

Status: Published in April 2013 (Worth noting: publication of ISO 15118-1 Ed. 2 is planned for Q4/2019)

Part 2 is called ISO 15118-2 and is titled “Network and application protocol requirements”. ISO 15118-2 is the core or the heart of the entire international standard because it defines all the messages and related technical requirements that are necessary to implement to realize the use cases defined in ISO 15118-1. 

If you want to dig deeper into this part, check out the ISO 15118 Manual. This in-depth guide to ISO 15118-2 is for both beginners and experts. You can also check out our online courses. There, you’ll find step-by-step guides, implementation examples, and hands-on exercises that will accelerate your understanding of the standard and help you design ISO 15118-compatible products.

Did you know there is an open-source implementation of ISO 15118-2 available? It’s called  RISE V2G, and you can use it to test your ISO 15118-compliant charging stations or electric vehicle. RISE V2G covers all aspects of ISO 15118-2 for AC and DC charging, including security related features like TLS and certificate handling to bring the tamper-proof and convenient Plug and Charge mechanism to life. 

Status: Published in April 2014

Part 3 is called “Physical and data link layer requirements” and defines lower-level communication (the data link layer and the physical layer). These layers establish the higher-level communication outlined in ISO 15118-2. This third part also refers to IEC 61851-1, a standard that describes how to process the analog, safety-related pulse width modulation (PWM) signals that encode the available amperage at a charging station. 

These PWM signals are controlled by the charging station and expressed as duty cycles given in percentages that range from 10% to 96%: the higher the duty cycle, the higher the available amperage and the quicker the EV can be charged. This was the usual way of charging EVs before ISO 15118 came into existence. The ISO 15118 Manual explains the PWM signaling mechanism in detail. If both the charging station and EV support ISO 15118-2 (or ISO 15118-20), they can use a PWM signal of 5% to trigger high-level communication. This means that they will engage in a charging process that is not controlled by analog PWM signals but instead by the information that is exchanged via the digital communication protocol ISO 15118. 

Moreover, ISO 15118-3 addresses how powerline communication (PLC) is used to modulate the digital information specified in ISO 15118-2 onto the Control Pilot (CP) pin inside the charging cable. Part 3 also describes a mechanism called SLAC (Signal Level Attenuation Characterization), which the EV and charging station use to establish the data link between each other and to cope with the crosstalk phenomenon that occurs in powerline communication networks. The HomePlug GreenPHY specification describes how PLC is used in the context of ISO 15118.

Status: Published in May 201

Part four of this family of ISO documents relates to conformance tests for the requirements specified in ISO 15118-2. Part five refers to the conformance tests for requirements defined by ISO 15118-3. A conformance test is a set of rules that describes whether a certain input of data is valid with respect to both the data itself and the current state of the system that is being tested (i.e. EV or charging station).

Status: Both published in February 2018

Part 6 is called “General information and use-case definition for wireless communication” and is one of the parts that made it to the official phase of a Draft International Standard (DIS). However, work on ISO/DIS 15118-6 has stopped, which means it will not be published as an international standard (IS). Instead, the ISO and IEC Joint Working Group decided to merge the outlined use cases and terms for wireless charging and communication with the existing ISO 15118-1 document. The result will be a second edition of ISO 15118-1. This means, you can safely ignore ISO/DIS 15118-6.

Status: To be published as part of ISO 15118-1 Edition 2 by end of 2019

Part 7 is called “Network and application protocol requirements for wireless communication.” This part was originally devised to add the technical requirements of wireless charging to the wired specifications outlined in ISO 151118-2. At first, the Joint Working Group decided to merge part two and part seven into a second edition of ISO 15118-2. However, as of January 2019, they decided not to publish all the new features in a second edition of ISO 15118-2, but instead to use a separate document number: ISO 15118-20. The anticipated publication date for ISO 15118-20 is the end of 2019 or the beginning of 2020. 

Status: There is no document behind ISO 15118-7 (although the title remains out of commission)

In contrast to parts six and seven, ISO 15118-8 remains as a separate part that specifies the technical requirements for wireless communication on the lowest two communication layers using IEEE 802.11n as Wi-Fi technology. Part 8 is called “Physical layer and data link layer requirements for wireless communication”.

Status: Published in March 2018

ISO 15118-9 is called “Physical and data link layer conformance test for wireless communication”. This specification provides conformance tests for the use cases in part eight and completes the current list of required conformance tests for both wired and wireless communication. 

Status: No publication date available yet

ISO 15118-20 is called “2nd generation network and application protocol requirements” and is an updated version of ISO 15118-2, with additional features like wireless charging, bidirectional energy transfer, and charging buses via pantographs. ISO 15118-20 will not be compatible with ISO 15118-2, meaning: an EV that only communicates via ISO 15118-2 will not be able to charge at a charging station that only supports ISO 15118-20—and vice versa.

Status: Publication planned for late 2019 or early 2020

The Process and Timeline for the
Publication of ISO Standards

Stages within the timeline for publishing ISO standards (Source: VDA)

The figure above outlines the timeline of a standardization 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 standardization 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. 

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