Wireless power transfer is seen as an ideal solution to the range and reliability challenge of electric vehicle ownership. Despite the ostensibly attractive environmental advantages of these vehicles, the almost primordial fear of being stranded far from home on a deserted road is widely perceived as one of the central barriers to the widespread uptake of electric vehicle technology.
“Electric vehicles are going to be the way we re-invent transportation and reduce the cost in terms of the environment,” says Ned Freeman, a member of the executive committee at Plugless Power (Evatran). “Given that, you start to think about what are some of the things that are holding consumers back when it comes to considering electric vehicles. Number one is range and life.” WPT offers a range of benefits in this respect.
IEC Technical Committee (TC) 69 develops International Standards for electric road vehicles and industrial trucks, totally or partly electrically propelled from self-contained power sources, including issues associated with WPT, which are addressed by JPT 61980: Electric vehicle wireless power transfer systems. IEC TC 69/JPT 61980 is a Joint Project Team set up by IEC TC 69 and a Subcommittee (SC) of the International Organization of Standardization (ISO) TC 22: Road vehicles, to develop International Standards for WPT.
Bridging the gap
Wireless power transfer describes a range of technologies which permit electrical energy to be transmitted to a source of demand without the need for conductive cables or making a physical connection.
Promising approaches include radio, microwave or even laser transmission, coupled capacitance and the most market-developed WPT technology to date – magnetic induction.
Similar to the induction charging systems found in the domestic environment on low-power devices such as electric toothbrushes, razors or inductive cookers, in an EV application, WPT induces an electrical current in an appropriately tuned coil. It is capable of delivering significant power – systems supplying several hundred kW are under development.
Certainly, inductive power transfer is the technology of choice for major auto manufacturers as they look to launch systems commercially in the coming years. It is also the technology behind the world’s first market-ready EV WPT system from Plugless.
It began a low-volume roll out of its L2 System – developed and manufactured by Evatran – in mid-2014, following more than two years of trials with partners including Google, Duke Energy, and Hertz. Currently available for the Chevrolet Volt and Nissan Leaf vehicles, a 7,2 kW system for the Tesla S is due for launch in the next few months.
It uses inductive power transfer from a transmitting coil in a parking pad and charges an EV as quickly as a plug-in Mode 2 (240 V) station. Mode 2 charging refers to the connection of an EV to the AC supply network (mains) not exceeding 32 A and not exceeding 250 V AC single-phase or 480 V AC three-phase utilizing standardized single-phase or three-phase socket-outlets, according to IEC 61851-1:2010, Electric vehicle conductive charging system – Part 1: General requirements.
“If you have an in-ground mount system, that’s what I would say is the candidate which has the most advantages,” says Dr Jochen Mahlein, who heads the LMS division at SEW-EURODRIVE. SEW-EURODRIVE has had experience in WPT for industrial applications for more than 16 years and is a member and secretary of IEC TC 69/JPT 61980.
For example, rather than poles, stanchions or other street furniture, inductive charging systems can be contained within a concrete pad that is flush with the road surface, and are therefore very difficult to damage, representing potentially low maintenance costs. It also solves the issue of the need for an appropriate plug at a charging point. Furthermore, Mahlein argues that the installation costs of a WPT system are comparable with those of existing wired alternatives.
Freeman also comments: “It’s obvious that wireless power transfer has unique advantages”.
For example, there is the possibility of ‘dynamic’ charging whilst a vehicle is in motion. Such systems are already in use in industrial environments and in August 2015 the UK’s Highways Agency began off-road trials of dynamic wireless power transfer.
The trials will involve replicating motorway conditions. The trials are expected to last for approximately 18 months.
Certainly there is some evidence of gathering momentum behind WPT technology for the EV market. A 2014 report from Navigant Research concludes: “Most wireless charging systems are in the pilot phase and are likely to remain there for another two to three years. […] Within a decade, wireless charging could be the leading way of charging EVs”.
Navigant forecasts that wireless charging equipment for light duty vehicles will grow by a compound annual growth rate of 108% from 2013 to 2022, reaching annual sales of some 300 000 units in 2022. Another recent forecast indicates that by 2019, WPT for the EV market is expected to be worth around USD 4,6 billion.
With the high power transfer capability of WPT comes the possibility of rapid charging.
There are already projects using high power systems for commercial vehicles and increasing power capacity is one key area of research. For instance, in March this year, a 20 kW wireless charging system was demonstrated at the US Department of Energy’s Oak Ridge National Laboratory running at 90% efficiency. Working with companies including Toyota and Evatran, the researchers say they are already looking ahead to their next target of a 50 kW WPT system.
Nissan is expected to launch a unit of more than 7 kW in the coming year, doubling the transfer capacity of its early developments. And Qualcomm has developed a 7,2 kW system, also doubling the capacity of its previous version.
However, at higher powers, safety becomes more of a concern, as Mahlein explains: “Current WPT systems are in a frequency range of 20 to 140 kHz. In terms of safety, 140-150 kHz is the starting point of broadcast radio applications; this is also something that needs to be borne in mind.”
As a result, mechanisms to address the possibility of animals, people or even waste such as aluminized paper entering a strong magnetic field are being looked at.
Oak Ridge’s Power Electronics Team lead, Madhu Chinthavali, picks up on this: “The high-frequency magnetic fields employed in power transfer across a large air gap are focused and shielded. This means that magnetic fringe fields decrease rapidly to levels well below limits set by international standards, including inside the vehicle, to ensure personal safety”.
The role of International Standards
IEC International Standards for issues associated with WPT are developed by IEC TC 69/JPT 61980.
This JPT, in which some 70 experts from 13 Participating Members are active, has already published IEC 61980-1:2015, which deals with general requirements for electric vehicle WPT systems, and is preparing additional Standards in the IEC 61980 series to cover specific requirements for communication between EVs and infrastructure, as well as for magnetic and electric field power transfer systems.
Mahlein outlines some of the key issues in developing appropriate Standards: “The process of finding a unique solution is still ongoing; we have to deal with a lot of demands. I think we have some good approaches in standardization to cover most of those demands and I think we’re close to finding a consensus in this for public infrastructure”.
The crucial role of standards in accelerating the roll-out of EV WPT is also picked up by Freeman, who says: “Interoperability is something that’s going to be transformative for wireless power transfer. Standards can be a key enabler of getting interoperability”.
Looking forward, he says: “Wireless charging as an after-market accessory is something I think we’ll see more of. In the near term, the key is to take away those everyday concerns at home by making it hands free and automatic with wireless power”.
Freeman concludes: “The success in terms of helping to catalyze EV adoption comes when people stop worrying about it”. Wireless Power Transfer is set to be a key enabler in achieving that goal.