Introduction to European Standard Charging Pile Communication Protocol

15118-1 mainly outlines the general requirements, covers the charging and billing process based on ISO 15118, and describes in detail the devices and their information interactions in various application scenarios.
15118-2 focuses on the application layer protocol, clarifies the messages, message order, state machines in various application scenarios, and the technical requirements required to implement these scenarios. It comprehensively defines the protocols at each layer from the network layer to the application layer.
15118-3 involves the link layer, using power carrier technology, and mainly defines the physical layer signaling and messages, which is not very relevant to software developers.
15118-4 is about testing, while 15118-5 focuses on the physical layer, which also does not require too much attention from software developers.

In addition, there are the yet-to-be-released 15118-8 and 15118-9, which deal with wireless aspects and the wireless physical layer, respectively.

Next, let's talk about ISO 15118-20. This is the latest version of ISO 15118, which is committed to becoming the communication standard for future electric vehicle (EV) charging. It began development at the end of 2015 and aims to eliminate the limitations in previous versions and support a full range of electric vehicles, including cars, motorcycles, trucks, buses, ships, and aircraft. This new version places special emphasis on plug-and-charge capabilities and supports wireless power transmission (WPT), providing various services through bidirectional power transmission (BPT) and automatic connection devices (ACD). Next, we will take a deep look at these new features and their timeline for market launch.

Since its proposal in 2011, the CCS charging standard has gone through several iterations. Initially, in order to solve the interoperability and charging convenience problems caused by different standards in the global electric vehicle market, the European Automobile Manufacturers Association (ACEA) proposed this standard proposal, which aims to integrate AC and DC charging systems. Its feature is the combined socket design of the connector physical interface, which is compatible with three charging modes: single-phase AC, three-phase AC and DC, providing electric vehicles with more flexible charging options. In 2012, the CCS Combo 0 standard was officially launched. Subsequently, in 2014, the CCS Combo 0 version was released, marking a major upgrade of the standard. This version not only significantly improves the charging power, but also supports faster DC charging, so it has been widely used in the European and North American markets. Since then, the CCS standard has been updated twice (CCS Combo 1 and CCS Combo 2) in 2017 and 2020 respectively, continuously optimizing charging power and safety.

Interface Overview
There are multiple international standards for charging interfaces for electric vehicles (EVs). These standards include German DIN, European EN, international ISO, and national GB, each with unique protocols and characteristics. It is critical to understand and follow these standards when exporting electric vehicles.

In the United States and Japan, Type 1 plugs and ports are widely used in these two markets because the power grid only supports single-phase AC charging.

In Europe, especially Germany, due to the need for three-phase charging, the CCS2 interface has become relatively complex, with various configurations, including single-phase AC, three-phase AC, low-power DC and high-power DC. It is worth noting that both the European and Chinese power grids support single-phase 240V and three-phase 400V connection methods. In order to meet this market demand, eight automobile companies such as Audi, BMW, Chrysler, Daimler, Ford, GM, Porsche and VW jointly proposed a new charging interface standard in October 2011 - Combined Charging System (CCS), which aims to support both AC and DC charging. The standard was later formally established as IEC 62196-3. Among them, the Type 2 port is designed to support both single-phase charging and three-phase charging, and the three-phase AC charging technology can effectively shorten the charging time of electric vehicles. In addition, the car's charging port also integrates both AC and DC functions. During the charging process, data communication between the electric vehicle (EV) and the charging pile (EVSE) is achieved through the Control Pilot (CP) interface.

The CP - Control Pilot interface is responsible for transmitting analog PWM signals and ISO 15118 or DIN70121 digital signals modulated onto analog signals based on power line carrier (PLC). The PP - Proxmity Pilot (also known as Plug Presence) interface is responsible for transmitting a signal that enables the vehicle (EV) to detect whether the charging gun plug is connected. This function is crucial to ensure charging safety because it prevents the vehicle from moving when the charging gun is connected. PE - Productive Earth, or ground protection, is the ground lead of the device for safety. In addition, there are several other interfaces for transmitting power, including Neutral (N) line, L1 (AC single phase), L2, L3 (AC three phase), and DC+ and DC- (direct current). Next, we will delve into the details of the ISO15118 protocol. The protocol uses a client-server model, in which the vehicle charging controller (EVCC) is responsible for sending request messages and the pile end charging controller (SECC) is responsible for returning response messages. The EVCC must receive a response from the SECC within a specific timeout range (usually 2 to 5 seconds), otherwise the session will be terminated. Depending on the implementation of different manufacturers, EVCC can re-initiate a new session.

Now, let's turn to the detailed analysis of the charging process.

During AC charging, you first need to ensure that the connection between the car and the charging pile has been established. Once the connection is successful, the vehicle charging controller (EVCC) will send a request to the pile-side charging controller (SECC) to start charging. After receiving the request, SECC will perform a series of verification and preparation work to ensure the safety and effectiveness of charging. If everything is normal, SECC will return a confirmation message to inform EVCC that charging can begin. At this point, the charging process is officially started, and the electric energy is transmitted to the car battery through the Neutral (N) line, L1 (AC single-phase), L2, L3 (AC three-phase) and other interfaces. During the charging process, EVCC will continue to monitor the charging status and maintain communication with SECC to ensure smooth charging. When charging is completed, SECC will send a message to EVCC to end charging, and the charging process will end.

During the DC charging process, it is also necessary to ensure that the connection between the car and the charging pile has been established. Similar to AC charging, the vehicle charging controller (EVCC) will also send a request to the pile-end charging controller (SECC) to start charging. The difference is that DC charging uses a higher voltage and current power transmission method. Once the SECC confirms and starts charging, the power will be directly transmitted to the car battery through the DC interface. During this process, the EVCC will also continue to monitor and maintain communication with the SECC to ensure safe and efficient charging. When charging is completed, the SECC will notify the EVCC to end charging, and the entire DC charging process will end.

The IEC 61851 standard defines a communication protocol that is closely related to charging safety, which is based on pulse width modulation (PWM) technology. The ISO 15118 standard further strengthens the communication between charging piles and electric vehicles, providing more comprehensive information exchange through advanced digital protocols, covering key functions such as two-way communication, channel encryption, authentication and authorization, charging status monitoring, and departure time management. Once the CP pin on the charging line detects a PWM signal with a 5% duty cycle, charging control is immediately transferred from other protocols to the ISO 15118 standard.

If the charging pile or car only supports the IEC 61851 communication protocol, then when a PWM signal with a 5% duty cycle is detected, the charging process will start with the maximum available charging current and continue until the car is fully charged. However, during this period, the charging station operator cannot know the total amount of power required by the car or the desired charging end time. But the ISO 15118 standard can provide this key information, which is essential for peak load shaving and valley filling of the power grid and more efficient services.

Core functions
(1) Smart charging
Smart EV charging involves intelligent control, management and optimization of all aspects of EV charging. It relies on real-time data communication between EVs, chargers, charging operators and power suppliers. In the smart charging ecosystem, all parties communicate continuously and adopt advanced charging solutions to improve charging efficiency. The core lies in the smart charging EV solution, which can process relevant data and give charging operators and users comprehensive management capabilities for charging links. Smart charging includes multiple functions:
A. Intelligent energy management to ensure that the impact of EV charging on the power grid and power supply is within a controllable range;
B. Optimizing EV charging to help drivers and charging service providers make the best decisions in terms of cost and efficiency;
C. Remote management and analysis to achieve charging control and adjustment through network platforms or mobile applications;
D. Advanced EV charging technologies, such as the implementation of new technologies such as V2G, also rely on the support of smart charging functions.

The ISO 15118 standard introduces a new source of information for smart charging - the electric vehicle itself. The energy that the car is expected to consume is a crucial piece of information when planning the charging process. This key data can be provided to the charge management system (CSMS) in a variety of ways, enabling intelligent control of the charging process.

The ISO 15118 standard introduces a new source of information for smart charging - the electric vehicle itself. The energy that the car is expected to consume is a crucial piece of information when planning the charging process. This key data can be provided to the charge management system (CSMS) in a variety of ways, enabling intelligent control of the charging process.

(2) Smart charging and grid management Smart electric vehicle charging is an integral part of the system, as the charging behavior of electric vehicles has a profound impact on the energy consumption of homes, buildings or public areas. There is an upper limit to the amount of electricity that the grid can handle at a certain moment. Smart charging technology can optimize charging behavior while ensuring a stable power supply, thereby reducing the pressure on the grid.

(3) Plug and charge technology
In 2014, the ISO 15118 standard was released, one of the important functions of which is plug and charge. This technology enables electric vehicles to automatically identify and start charging when connected to a charging pile without human intervention, which greatly facilitates users.

(4) TLS communication technology

TLS (Transport Layer Security) communication technology, as a security protocol, is widely used in network communications. It can establish an encrypted channel between electric vehicles and charging piles to ensure the security of data transmission and provide strong protection for users' charging behavior.

(5) Key verification
In TLS communication technology, key verification is a crucial link. It ensures the authenticity of the identities of both parties in communication and the integrity of the data. Through key verification, electric vehicles and charging piles can confirm each other's identities, thereby establishing a secure and reliable communication link.

Comparison of charging pile protocols
The IEC 61851 standard not only ensures that the charging current is activated only when a stationary vehicle is connected, but also has analog, safety-related low-level charging control functions. On this basis, IEC 62196 and ISO 15118 have been further developed, both with IEC 61851 as the cornerstone. The CP line in the IEC 62196 plug can distinguish 6 electric vehicle connection states and indicate the maximum charging current allowed by the charging pile through an analog PWM signal. However, to achieve flexible charging management of multiple electric vehicles, more basic parameters are required, which cannot be transmitted separately through PWM analog signals. Therefore, the need for digital communication protocols came into being, and the ISO 15118 protocol was born in this context. It is worth noting that the DIN 70121 standard is based on an early unpublished version of ISO 15118. In addition, the GB/T 27930 communication protocol was designed for specific application scenarios of domestic electric vehicle charging facilities.

IEC 61851 Protocol
IEC 61851-1 is one of the important standards that defined the charging requirements of electric vehicles in the early days. It specifies four charging modes, of which mode 2 specifically uses PWM signals as a means of communication between the EV and the off-board charger, which is transmitted through the pilot line. Mode 4 further develops the function of high-level communication (HLC) through the pilot signal line to achieve effective management and communication of direct current charging (DC) defined in IEC 61851-23. The charging pile will send out a 1kHz PWM signal, but the actual charging current is determined by the vehicle (EV) based on the information received. In addition, pulse width modulation technology plays a key role in this process. It is a modulation technology that encodes information, such as the maximum allowed charging current, into a pulse signal. Its working principle is to control the voltage amplitude and switching time of the CP signal at the output port of the charging pile. The ratio of the power on and off time, that is, the "duty cycle", is expressed in percentage form, which reflects the level of available charging current. At the same time, the voltage difference [V] between the voltage on the CP line and the ground wire (PE) is used to distinguish different connection states between the pile and the car.

DIN70121 protocol
The DIN 70121 standard was issued by the German Institute for Standardization in 2012. It provides specifications for digital communication between electric vehicles and DC charging piles. When the ISO/IEC 15118 standard was still being drafted, the German automotive industry urgently needed a standard to lead the market and promote product launches. Therefore, DIN 70121 came into being, carrying the heavy responsibility of promoting the electrification transformation of German automobiles. This standard is based on IEC 61851-23 and the early version of ISO 15118, and specifies in detail the digital communication specifications during the DC charging process, including the HLC over Pilot signal between EV and EVSE. It is worth mentioning that when DIN 70121 was released, PLC (as described in the HomePlug Green PHY specification) was widely used in North America and Europe as the physical layer and data link layer of the HLC protocol. This standard not only solved the problem of lack of standards in the DC charging industry at that time, but also brought a new communication mode and specification to the industry, promoting the development of the industry. In 2014, the German Institute for Standardization further released DIN 70121:2014 Ed.2 to improve the original standard. In 2018, they officially launched the consistency test specification DIN 70122:2018 for DIN 70121, providing a comprehensive and rigorous standard and testing system for CCS charging.

SAE J1772 Protocol
The SAE J1772 standard was developed by the Society of Automotive Engineers (SAE) to standardize different types of charging protocols. The standard uses the HLC protocol of DIN70121 for DC charging and the Pilot PWM signal of IEC 61851-1 for AC charging. In addition, SAE J1772 also defines in detail the PWM waveform for controlling the Pilot signal in the EV-EVSE interface during AC charging. In addition, SAE J1772 and SAE J2847-2 protocols jointly describe the message timing and sequence of vehicle-to-grid (V2G) communication based on DIN70121.

ISO15118 protocol
ISO 15118 is a comprehensive protocol standard that covers the security of the HLC protocol for both AC and DC charging sessions. The standard introduces two methods for charging user identification: External Identification Mode (EIM) and Plug and Charge (PnC) mode. The EIM mode is similar to DIN 70121 or SAE J2847, requiring car drivers to manually authenticate using a credit card or other identification method before charging begins; while the PnC mode allows identification and billing information to be automatically exchanged between EV and EVSE via HLC without the need for manual operation by the driver. In addition, unlike DIN SPEC 70121, ISO 15118 also provides the function of intelligently scheduling charging time based on grid capacity and energy costs.

(1) Both DIN 70121 and ISO15118 are based on PLC communication, while GB/T 27930 uses CAN communication as the basis.
Power line communication (PLC) technology based on the HomePlug GreenPHY protocol couples OFDM modulated high-frequency signals with CP signal lines through a modem installed in the charging pile or vehicle CP signal circuit. The modem at the other end is responsible for demodulating these signals, thereby achieving a communication rate of up to 10 Mbit/s without adding additional communication pins. This technology provides a high-bandwidth channel for DC charging information interaction, while supporting advanced features such as plug-and-play charging and vehicle-network interaction.

(2) Comparison between ISO15118 and IEC 61851
The IEC 61851 standard uses pulse width modulation (PWM), which is an analog signal. If the charging station or car only follows this protocol, the charging process will start with the maximum available current until the car is fully charged, and the charging station operator will have no idea about the actual power demand or the end time of charging. In contrast, if the system supports ISO15118, when a PWM signal with a 5% duty cycle is detected, charging control will be immediately transferred to ISO15118, achieving smarter charging management.
(3) Extended functions of ISO15118
In addition to traditional conductive charging, ISO15118 also covers V2G (vehicle to grid) plug-and-play functions, wireless charging, etc. In contrast, the DIN70121 standard does not support plug-and-play, lacks secure communication and digital signature mechanisms, and cannot guarantee data authenticity and integrity. In addition, it is only applicable to DC charging mode, while ISO 15118 supports both AC and DC charging.
(4) Relationship and differences between DIN 70121 and ISO 15118
The DIN 70121 standard is based on an earlier unpublished version of ISO 15118 and is mainly used to define digital communication between electric vehicles and DC charging stations. However, it only covers the DC charging mode, while ISO 15118 is more comprehensive and supports both AC and DC charging. Figure 1 shows the main functional differences between the two versions.