2 February 2012

Wireless charging proposed for electric cars

by Will Parker

An innovative wireless system that charges electric cars while they are on the road could also be used to control driverless electric vehicles, say the Stanford University team who designed the system. While the new technology has the potential to dramatically increase the driving range of electric vehicles, the researchers concede that large-scale deployment of the system would involve revamping the entire highway system.

According to the researchers, their charge-as-you-drive system would overcome one of the major limitations of electric vehicles - limited range. "What makes this concept exciting is that you could potentially drive for an unlimited amount of time without having to recharge," said study co-author Richard Sassoon. "You could actually have more energy stored in your battery at the end of your trip than you started with."

The system is based on a technology known as magnetic resonance coupling where two copper coils placed a few feet apart are tuned to resonate at the same frequency. One coil is connected to an electric current, which generates a magnetic field that causes the second coil to resonate. This magnetic resonance results in the wireless transfer of electrical energy from the first coil to the receiving coil. Receiving coils attached to the bottom of the car would resonate as the vehicle speeds along, creating magnetic fields that continuously transfer electricity to charge the battery.

The Stanford research, published in Applied Physics Letters, builds on previous research at MIT that detailed a stationary charging system capable of wirelessly transferring about 3 kilowatts of electric power to a vehicle parked in a garage or on the street. The Stanford researchers wondered if the MIT system could be modified to transfer 10 kilowatts of electric power over a distance of 6.5 feet - enough to charge a car moving at highway speeds. Using computer models, they found the answer: a coil bent at a 90-degree angle and attached to a metal plate can transfer 10 kilowatts of electrical energy to an identical coil 6.5 feet away. "This wireless transfer scheme has an efficiency of 97 percent," boasted Stanford's Shanhui Fan.

Fan says the next step is to test it in the laboratory and eventually try it out in real driving conditions. The researchers also want to make sure that the system won't affect drivers, passengers or the dozens of microcomputers that control steering, navigation, air conditioning and other vehicle operations.

The wireless charging system would also offer the possibility of an automated highway system with driverless electric vehicles, which the researchers say would reduce accidents and dramatically improve the flow of traffic. "The magnetic fields could also be used to control steering," they note. "Since the coils would be in the center of the lane, they could provide very precise positioning at no extra cost."

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Source: Stanford University