Understanding the ISO 15118 standard EV smart grid integration

ISO 15118, known as “Road vehicles – Vehicle to grid communication interface,” is an international standard that outlines the communication protocol between EVs and the charging infrastructure, including smart grids. It enables advanced functionalities such as Plug and Charge, bidirectional power flow, and smart charging.

How are EVs and smart grids related to each other?
Figure 1 shows the integration of electric vehicles (EVs) into the smart grid, allowing them to act as mobile energy storage units that can support grid stability and the efficient use of renewable energy sources. Integrating EVs into the smart grid also facilitates the implementation of vehicle-to-grid (V2G) technologies.

Figure 1. A smart grid-EV ecosystem comprising renewable energy, EVs, smart meters, energy storage systems, and communication. (Image: IEEE Access)

What are the various parts of the ISO 15118 standard?
ISO 15118 consists of several parts and is collectively called a standard. The different parts are shown in Figure 2. All the parts are assigned to one or more than one of the seven Open Systems Interconnection (OSI) layers.

Figure 2. The different parts of ISO 15118 standard and the relationship with the OSI layers. (Image: Switch EV)

Part 1 defines terms and use cases covering all seven layers. Part 2 forms the standard’s core, where all the application layer messages concerning the EV charging communication are explained in detail.

Part 3 deals with the lowest two layers – physical and data link layers meant for wired charging. Higher-level communication is established with the use of these two layers. Parts 4 and 5 are conformance tests applicable to parts 2 and 3.

Part 6 was meant for “General information and use-case definition for wireless communication,” which will be merged in the second edition of the standard with wired charging.

“Network and application protocol requirements for wireless communication” is part 7. Similar to the previous part, this part is merged with part 2. Part 8 is a standalone technical document and deals with the OSI layer 1 and OSI layer 2. Part 9 is the newest addition, offering guidance on conformance tests for part 8.

What are the notable features of ISO 15118?
The salient features of the ISO 15118 standard are Plug and Charge, V2G communication, smart charging, and interoperability, as shown in Figure 3.

Figure 3. Four salient features of ISO 15118 standard. (Image: Rakesh Kumar, Ph.D.)

Plug and charge
ISO 15118 facilitates a seamless Plug and Charge experience by automating the authentication and billing process when an EV is connected to a compatible charging station. This means drivers can simply plug in their vehicle to start charging without needing additional apps or cards.

The standard employs cryptographic mechanisms to ensure secure communication protocols between EVs and charging stations. These mechanisms include digital certificates and public key infrastructure (PKI) to enable authentication and secure data exchange.

V2G communication
V2G communication is a core feature of ISO 15118, enabling bi-directional energy flow and allowing EVs to draw power from the grid and supply energy back to it. This capability is essential for balancing demand and supply in the grid, especially with fluctuating renewable energy sources.

V2G can also support grid stability by providing ancillary services like frequency regulation, load balancing, and peak shaving. The ISO 15118 standard also mentions the wired and wireless communications protocols, detailing how EVs interact with charging stations for energy transfer and data exchange.

Smart charging
ISO 15118 supports smart charging strategies that consider grid load, energy prices, and renewable energy availability, allowing for the optimization of charging times and rates.

The standard enables participation in demand response programs, where charging can be adjusted based on grid needs to prevent overloads and efficiently use energy resources.

Interoperability
By establishing a standard communication protocol, ISO 15118 ensures interoperability between different EVs and charging infrastructure, promoting a wide-scale adoption of EVs.

The standard is designed to be forward-compatible, accommodating future technological advancements in EV charging and grid integration.

Summary
The ISO 15118 standard for EV charging communication with the smart grid is necessary to ensure interoperability, security, and efficiency. It allows vehicles from different manufacturers to communicate seamlessly with various charging stations and grid operators, making the charging process user-friendly and consistent.

It also ensures that the data exchanged during charging sessions is secure, protecting user information and energy transactions. A standard protocol facilitates the integration of EVs as active participants in the smart grid, capable of smart charging and contributing to energy balancing, thereby enhancing the overall resilience and sustainability of the power system.

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