Level 3, dc fast charging, is expected to help reduce range anxiety by speeding the EV charging process. However, fast dc chargers are expensive and can be challenging to connect to the grid, which is expected to slow their widespread use.
On the other hand, wireless power transfer (WPT) charging is currently limited to much lower power levels. It’s easy to install, low in cost, and expected to enable the deployment of many charging stations, contributing to reduced range anxiety for EV drivers.
This article reviews several international standards related to Level 3 fast dc charging and newer standards from the International Electrotechnical Commission (IEC) and SAE International for WPT EV charging.
Level 3 charging
Some of the standards that apply to Level 3 fast dc charging, starting with the connections to the utility distribution network and continuing to the EV, include (Figure 1):
- IEC 61930 and EN 50522 apply to medium-voltage to low-voltage (MV/LV) transformers in the utility distribution network.
- IEC 61439 applies to enclosures with a rated voltage of 1,000 Vac or 1,500 Vdc.
- IEC 60364-7-772 applies to EV charger electronics and includes requirements for feeding electricity back from EVs to the grid.
- IEC 61851 applies to EV chargers and covers the charger’s characteristics and operating conditions, the specification of the connection between the charger and the EV, and various requirements for electrical safety.
- IEC 62893 specifies construction, dimensions, and test requirements for cables rated to 1,500 Vdc for use in equipment like dc fast chargers. It includes requirements for carrying power and refers to the IEC 62196 series for plugs and sockets and IEC 61851-1 for related communications requirements. The charging cables are applicable for charging modes 1 to 4 of IEC 61851-1
- IEC 62196 is a standards series that defines requirements and tests for plugs, socket outlets, vehicle connectors, and vehicle inlets for conductive charging of EVs.
Figure 1. There’s a range of IEC standards for EV charging — from the MV/LV transformer interface to the distribution grid through the LV switchgear and building service entrance to the fast dc charger and the interface to the EV. (Image: TU Graz, Institute of Electrical Power Systems).
IEC and WPT
IEC 60364-7-722 Edition 2 recognizes the possibility of WPT chargers for EVs and requires compliance with IEC 61980. IEC 61980 currently includes requirements for inductive wireless power transfer, also called magnetic field wireless power transfer (MF-WPT). The requirements in IEC 61980 may be extended in the future to include additional WPT technologies like:
- Capacitive power transfer, also called energy transfer through the electric field (EF-WPT).
- Microwave power transfer is energy transfer through electromagnetic waves 1 to 300 GHz (MW-WPT).
- Infrared power transfer is energy transfer through electromagnetic waves 300 GHz to 400 THz (IR-WPT).
Various parts of IEC 61980 address requirements for wireless communication between the WPT system and the EV. In the case of MF-WPT, important considerations also include efficiency requirements, electrical safety, and electromagnetic compatibility (EMC).
SAE and WPT
The SAE International J2954 standard for wireless power transfer (WPT) is aimed at speeding the charging of EVs and autonomous vehicles. Tests using a 250 mm (10 inch) ground clearance show that WPT systems can deliver up to 94% grid-to-battery efficiencies. The optional alignment elements in SAE J2954 can enable EVs to charge themselves without human intervention.
The standard defines two sides to a WPT system, the ground assembly (GA) and the vehicle assembly (VA), and includes three power levels:
- WPT1, 3.7 kW
- WPT2, 7 kW
- WPT3, 11 kW
A second standard, SAE J2847/6, Communication for Wireless Power Transfer Between Light-Duty Plug-in Electric Vehicles and Wireless EV Charging Stations, using Wi-Fi, IEEE 802.11n, was developed specifically for use with SAE J2984 WPT systems (Figure 2).
Figure 2. Like the IEC, SAE WPT EV charging standards have specific documents that cover power transfer and wireless communications. (Image: SAE)
Summary
The availability of Level 3 dc fast charging and WPT opportunity charging are both expected to be important developments in reducing range anxiety for EV drivers. In the case of fast dc charging, the IEC has a comprehensive suite of standards that extend from the utility distribution network to the EV charger interface. For WPT charging, the IEC and SAE address the need for safe, reliable, and efficient power transfer and wireless communications between the charger and the EV.
References
- Charging Infrastructure for Electric Vehicles, TU Graz, Institute of Electrical Power Systems
- Developing Infrastructure to Charge Electric Vehicles, US Department of Energy
- Developments in International Standards for supplies for electric vehicles, The Institution of Engineering and Technology
- Electric Vehicle (EV) Charging Infrastructure Services, UL
- New SAE Wireless Charging standard is EV game-changer, SAE
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