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Charging Electric Vehicles Wirelessly

12 August 2014

Most of our devices can now be charged wirelessly, so that cables are not as important as they were years ago. Our smartphone, toothbrush, and headphones all can be charged through standard wireless techniques via electromagnetic induction.

Charging an electric car wirelessly is a much bigger task that is still in the distant future, but researchers at the Fraunhofer Institute for Integrated Systems and Device Technology IISB in Erlangen, Germany are developing a means of charging EV batteries wirelessly. "Cables are annoying, especially in winter or when it's raining. Whatever gets on the cable -- snow, sludge, water -- also gets on your hands," says Dr. Bernd Eckardt, head of the Vehicle Power Electronics department at Frauhofer.

According to Dr. Eckardt, the way to do this is to use electromagnetic induction to transfer electric energy between the vehicle and the supply. The physics behind this process is explained by Dr. Eckardt as follows: "Any wire that carries a current generates a magnetic field. As the English physicist Michael Faraday demonstrated in the 19th century, this magnetic field generates voltage or electromotive force as well. By correctly positioning two wires in relation to one another inside a magnetic field, it is possible to transmit energy over the air. In principle this works just like a transected transformer."

Scientists have been experimenting with using induction to charge electric car batteries for years, but without much success. The approach used so far involves mounting induction coils under the car and installing charging stations in the ground. The main problem with this technique, among many others, is that the coils have to be able to handle large amounts of power because of the relatively large gap (up to 15 cm) between the vehicle and the ground. Such coils are very expensive, pushing up the cost of the system. Another problem is that objects or animals can interrupt the transfer of energy if put between the car and ground.

The Fraunhofer team developed a simpler system. They created a technique to charge an electric vehicle at its front end. If the coils are located in the front end it is possible to drive the car as close as possible to the induction source – in fact the vehicle's coils can touch the source. The gap in this system is smaller and the coils can be made smaller as well, making the system cost-effective. The Fraunhofer team also discovered that the system is much more efficient. Because the gap is small the system is less prone to encounter objects that disrupt the flow of energy.

By installing charging systems at the front of the vehicle, scientists have found a new efficient and cost-effective approach. (© Fraunhofer IISB)

Scientists at the IISB have been working on general vehicular electronics for the past twelve years, and on induction for the past two years. "We've been consistently upping the system's performance over the past year, and are now in possession of a prototype that is able to transmit three kilowatts (kW) at an overall efficiency of 95 percent. Today's electric car models can be recharged overnight," says Eckardt. "Nowadays, charge spots are offered as part of the sales package when customers buy an electric vehicle. This technology will only become a mass product if the price is right," Eckardt explains.

The result of the research appeared on July 30, 2014 on the Fraunhover Research News website.

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