EV charging standards: Ensuring compatibility and safety in the charging process

Introduction

EV charging standards are instructions and guidelines that ensure the safe and compatible charging of electric vehicles (EVs). These standards include electrical specifications, grounding requirements, and other safety features crucial for promoting EV adoption and growth. The standards for EV chargers, also known as electric vehicle supply equipment (EVSE), vary by country and depend on the available EV models and electrical grid characteristics. Charging standards govern the connection between the EV and the EVSE, including physical connectors, communication protocols, and electrical parameters for charging electric vehicles. By adhering to these standards, various types of vehicles can ensure compatibility with multiple types of electric vehicles.

Charging standards

Charging standards are developed by international organisations such as the International Electrotechnical Commission (IEC) and the Society of Automotive Engineers (SAE). These organisations bring together technical experts, manufacturers, and government agencies to create standards that are widely adopted by the industry. Some countries also have national standards organisations that may differ slightly from the international standards. To ensure compatibility and ease of use for EV owners, most EVs and charging stations are designed to be compatible with international and national standards.

a) Society of Automotive Engineers (SAE)

SAE has developed two standards related explicitly to charging electric vehicles: SAE J1772 and SAE J3068. The SAE J1772 governs AC charging for Levels 1 and 2, including the charging connector (the "J1772 plug") and communication between the EV and the charging station. The standard supports a range of single-phase AC charging rates, from portable devices that can connect to a standard 120-volt outlet to home and public charging stations with higher power levels. It includes plug type; current type; current phase; wattage; voltage; plug size; plug shape; cord length; and plug color.

The SAE J3068, in contrast, covers DC fast charging, including specifications for the charging connector and communication protocols.

b) International Electrotechnical Commission (IEC)

IEC 61851-1, IEC 61851-23, and IEC 62196 are key standards that provide technical specifications for charging connectors, communication protocols, and other components of EV charging systems.

• IEC 61851-1 is a standard for AC charging that covers the physical connection between the EV and the charging station and communication protocols between the two.
• IEC 61851-23 is a standard for DC fast charging that also covers the physical connection between the EV and the charging station and communication protocols.
• IEC 62196 is standard for AC and DC charging, covering the charging connector and communication protocols.

EV charging levels

Electricity distribution systems supply AC power, which must be converted to DC power for charging the battery pack in EVs. This is done using a converter. Figure 1. depicts the charging process of electric vehicles through AC or DC infrastructure. DC charging provides considerably faster charging speeds than AC charging. An AC EVSE employs the onboard charger of the EV to convert the AC power delivered by the charging station into DC power. Conversely, a DC EVSE directly supplies DC power to the battery by converting the power externally, bypassing the onboard charger.

Figure 1: The basic structure of a bi-directional EV charging

There are three levels of EV charging:

• Level 1 (L1) charging is the most basic and affordable option. This is typically done through standard 120V outlets and can take up to 8 hours to charge a vehicle. L1 charging is ideal for those with minimal EV needs or who need access to higher-level chargers. It delivers low power loads (1-2 kW) and has relatively longer EV charge times (approximately 4 miles/6.4 km of light-duty vehicle range per hour of charging).
• Level 2 (L2) charging uses AC to deliver power through a specialised higher-voltage connection. This is the most common type of charging used at home and in public, delivering between 6.6 kW and 19 kW of power. It requires a 240V outlet and takes 4-6 hours to recharge a vehicle fully. L2 charging is the most convenient vehicle charge and is widely available in public locations.
• Level 3 (L3) charging, also known as DC Fast Charging, is the fastest way to charge an EV. This type of charging is only supported by specific vehicle models and requires specialised equipment. It provides high power levels (50-400 kW) using specialised charging equipment and can give an 80 per cent charge in as little as 30 minutes. Table-1 summarises the different levels of charging.


Table 1: EV charger type classifications

Modes of EV charging

There are four different charging modes. These are called modes 1, 2, 3, and 4, specified by the IEC 61851 standard. Figure 2 illustrates the different modes of connecting EV chargers.



Figure 2: Different EV charging methods

• In Mode 1 charging, an EV uses a cable and plug to connect to a standard household socket outlet. There needs to be more communication between the EV and the EVSE, so it is occasionally used.
• Mode 2 uses a particular type of charging cable equipped with an in-cable control and protection device (IC-CPD). The inbuilt protection and control capability prevents overcharging and ensures safety and efficiency. This makes it suitable for home charging. The maximum current of this mode is 32 A. Mode 2 can be used with both household and industrial sockets (250 V single-phase or 480 V three-phase)
• Mode 3 charging utilises an EVSE that communicates with the vehicle to negotiate the charging parameters, such as charging speed and time and can also provide feedback on the charging process. It utilises a dedicated EVSE along with the EV onboard charger. The maximum current of this charging mode is 250 A with either a 250 V 1-phase or 480 V 3-phase network.
• Mode 4 charging, also known as DC fast charging, bypassing the onboard charger, uses a high-power charger that directly provides DC power to the vehicle's battery. It can provide 600 V DC with a maximum current of 400 A and demands a higher level of communication and stricter safety features. It can charge an EV up to 80% in as little as 30 minutes.

Rapid charging standards

Rapid charging is a type of charging for electric vehicles (EVs) that can provide faster charging than normal charging. Rapid charging typically uses a high-powered charging station, which can provide a large amount of electrical power to the EV's battery in a short amount of time. There are several different rapid charging standards used around the world, including CHAdeMO, Combo Charging System (CCS), Tesla Supercharger, and GB/T. Each of these standards uses a different connector and communication protocol, which means that they are largely incompatible with one another.

EV charging standard connectors

EV standards provide guidelines for manufacturers to create an EVSE that can be connected to a vehicle's charging inlet. These guidelines cover the shape and size of the connector, as well as basic safety requirements and charging limitations.

Figure 3 displays the EV connectors used worldwide for AC and DC charging. AC charging uses power directly from the electric grid, whilst DC charging requires two additional dedicated DC pins. Additionally, all chargers require extra pins for communication or controls.



Figure 3: Depiction of different AC and DC EV connectors



Table 2: EV charging connector used by different levels of charging station

Wireless EV charging standard

This is a newer technology that allows EVs to charge without the need for cables or plugs. Wireless charging technology is becoming increasingly popular as it allows EV owners to charge their vehicles without having to plug in a physical cable.

SAE J2954 is a wireless charging standard developed by the Society of Automotive Engineers (SAE) that outlines the technical requirements for wireless power transfer (WPT) systems used for EVs and autonomous vehicles. The SAE J2954 standard defines the technical requirements for both the charging pad and the receiving pad, including the power output, frequency, and communication protocol. WPT systems work by parking in a wireless charging spot, with the vehicle positioned over an SAE J2954-compatible ground assembly pad. After a communications handshake, charging begins automatically without a physical corded connection.