Electric Cars: Charging On The Move

Published on Wednesday, 30 November 2011 09:38

	By Robin Whitlock Follow @RobinWhitlock66

One of the common criticisms of electric vehicles is that they just can’t compete with conventionally fuelled vehicles with regard to battery life and driving range.

 However, that may be about to change if scientists successfully manage to develop a wireless charging system that energises vehicles while they are on the move, part of a process called Contactless Power Transfer (CPT).

Research currently being conducted at the Centre for Automotive Research at Stanford University in California indicates that it may be possible to use magnetic coils embedded in road surfaces to create a weak magnetic field which resonates with a coil embedded in cars, thereby charging electric vehicles as they travel.

The research, currently being conducted by scientist Shanhui Fan and his team, follows earlier trials conducted in 2007 at the Massachusetts Institute of Technology (MIT) which demonstrated that magnetic resonance could be used to transfer power wirelessly between two stationary objects at a distance of 2 metres.

Fan has taken this a step further by suggesting that it may be possible to achieve the same power transfer at typical highway speeds and at levels sufficient to propel electric vehicles. His research suggests that it may be possible to transfer around 10 kW of energy with a 97 percent level of efficiency within 7 microseconds using a system of resonant coils and discs.

Admittedly the team have yet to actually build such a system, but Fan claims that two main benefits could be that drivers will be able to travel across large distances without fear of being stranded and also that electric car batteries could be reduced in size, thereby reducing costs.

Such research seems to be going on all over the world in fact. For instance the concept is the subject of a Japanese paper published in 2009 in the World Electric Journal written by Takehiro Imura, Toshiyuki Ichida and Yoichi Hori from the University of Tokyo. In New Zealand HaloIPT is working on has already unveiled a similar system. 

BMW and Siemens have also developed systems that can charge an EV while standing stationary, for example as in the case of electric taxi’s standing at a taxi rank. These are known as ‘park-and-charge’ systems and there is at least one such system available already, the WiTricity WiT-3300.

The use of oscillating magnetic fields in such research ensures that there is no safety issues involved since oscillating magnetic fields interaction with biological organisms is very weak. The power transfer only occurs when two circuits are resonating with each other which means that the system can be turned off merely by tuning the resonant frequency circuit accordingly.

The Stanford experiment goes further than the MIT research by advocating a series of coils placed beneath the road surface delivering energy to vehicles moving above. The scientists believe that an energy level of 10-20 kW should be sufficient.

These are exciting developments and definitely something to watch in the near future.