EVs charging wirelessly

Future EVs may not need to plug in to charge their batteries

By Morand Fachot

The growing number of electric vehicles (EVs) on the roads relies on cabled connections to the grid for charging. Wireless power transfer (WPT) is seen as an attractive alternative to plug-in charging. The IEC has published the first in a series of International Standards aimed at paving the way to the adoption of WPT for EV charging.

WPT EV charging Tokyo Demonstration of WPT EV charging at Tokyo Motor Show 2011 (photo: NJo)

EVs on the march

With growing concern about the environmental impact of vehicles powered by internal combustion engines (ICEs), EVs represent an attractive solution for the future of personal and public transport.

Hybrid EVs, which initially relied on various technologies such as regenerative braking or an ICE to recharge their batteries, first became available in the late 1990s. The introduction of plug-in hybrid EVs (PHEVs), which can be recharged by connecting a plug to the grid, marked an advance on ICE-hybrid EVs, with a longer all-electric range. There are some 10 million hybrid EVs on the roads today.

By mid-September 2015, the global number of plug-in EVs broke the one million mark, with all-electric EVs making up 62% of the total and PHEVs 38%.

Drawbacks of plug-in EVs

As their description indicates, for charging their batteries, plug-in EVs must be connected to the power grid through a cable and a plug. It is rare to find charging points in public places and on streets in most countries and they are costly to install. Furthermore, many are being damaged either accidentally or intentionally (theft of cable, hostility to EVs, etc.).

A solution in the form of WPT can prove attractive if it can be deployed.

IEC Technical Committee (TC) 69: Electric road vehicles and electric industrial trucks, has been developing International Standards for WPT.

The first of these Standards, IEC 61980-1:2015, Electric vehicle wireless power transfer (WPT) systems – Part 1: General requirements, was published in July 2015.

Setting the groundwork

IEC 61980-1 covers general requirements for WPT for EVs.

The requirements for the various WPT technologies are very different and will be treated in technology-specific parts of the 61980 series. These technologies include:

  • Inductive power transfer, in which energy is transferred through magnetic field (MF-WPT). This includes technologies utilizing magnetic resonance
  • Capacitive power transfer, in which the energy is transferred through an electric field (EF-WPT)
  • Microwave power transfer, in which the energy is transferred through electromagnetic waves in the range 1 GHz - 300 GHz (MW-WPT)
  • Infrared power transfer, in which the energy is transferred through electromagnetic waves in the range 300 GHz – 400 THz range (IR-WPT)

Interoperability of a WPT system is only achievable when the primary devices (which provide the contactless coupling) and the secondary devices (mounted on the EV) employ the same type of transfer technology.

The efficiency will be specified in the technology-specific parts of IEC 61980 series.

Multiple aspects

The scope of this part of IEC 61980 states that it "applies to the equipment for the wireless transfer of electric power from the supply network to electric road vehicles for purposes of supplying electric energy to the rechargeable energy storage system (RESS) and/or other on-board electrical systems in an operational state when connected to the supply network, at standard supply voltages ratings per IEC 60038 up to 1 000 V AC and up to 1 500 V DC".

It "also applies to WPT equipment supplied from on-site storage systems (e.g. buffer batteries, etc.)".

Aspects covered in IEC 61980-1 include:

  • the characteristics and operating conditions
  • the specification for the required level of electrical safety
  • requirements for basic communication for safety and process matters if required by a WPT system
  • requirements for basic positioning of the primary and secondary devices, efficiency and process matters if required by a WPT system
  • requirements for two- and three-wheel vehicles (under consideration)
  • requirements for dynamic WPT system while driving (under consideration)
  • requirements for bidirectional power transfer (under consideration)
  • specific EMC requirements for WPT systems

However, this Standard does not apply to safety aspects related to maintenance or to trolley buses, rail vehicles and vehicles designed primarily for off-road use.

Installation and environmental conditions

IEC 61980-1 lists the various types of installation, which depend on the type of secondary device on the EV:

  • ground mounted, including:
  •    in-ground mounted (e.g. under road surface)
  •    on-ground mounted
  •    over stand (e.g. for motorbikes, scooters)
  • vertical surface mounted (e.g. wall mounted)
  • on-roof mounted.

Furthermore, the Standard classifies the EV WPT supply equipment according to environmental conditions and use: indoor use, outdoor use or industrial area exposed to pollution and/or severe conditions.

Comprehensive scope covers multiple requirements

A non-exhaustive list of general and constructional requirements contained in this Standard includes, in addition to classification, interoperability, installation and environmental conditions, control and communication between the EV supply equipment and the EV, protection against electric shock and EMC-related immunity and disturbance requirements. Service and test conditions are also detailed and a number of use cases are described.

This first Standard in the IEC 61980 series focuses currently on stationary WPT systems. However the technology is expected to lead eventually to dynamic WPT-enabled infrastructure where EVs can be charged continuously while in motion, solving the EV battery problem with unlimited driving range.

IEC 61980-1:2015 is a decisive first step on the road to WPT adoption.

WPT EV charging Tokyo Demonstration of WPT EV charging at Tokyo Motor Show 2011 (photo: NJo)
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