Scientists at Stanford University's Department of Electrical Engineering have developed a dynamic wireless charging technology that can transmit electricity to moving objects and vehicles. Such an advance could solve the current problem of "range anxiety," wherein electric cars are feared to run out of juice before reaching their destination or a charging station.
“In theory, one could drive for an unlimited amount of time without having to stop to recharge,” said Shanhui Fan, a professor of electrical engineering at Stanford and research team leader. “The hope is that you’ll be able to charge your electric car while you’re driving down the highway. A coil in the bottom of the vehicle could receive electricity from a series of coils connected to an electric current embedded in the road.”
Magnetic field coupling forms the basis for the Stanford group's wireless charging technology, which is similar to efforts by a few other research groups in the academe and industry. Qualcomm last month unveiled its dynamic electric vehicle charging (DEVC) wireless technology, which uses charging pads embedded on the road surface to transfer power wirelessly to receiving parts onboard moving vehicles.
However, efficient power transfer can only be achieved if both transmitting and receiving coils are stationary, or manually tuned as the object moves. The Stanford team sought to enable frequency tuning as an automatic process, devoid of human intervention, by eliminating the RF source in the transmitter and replacing it with a commercially available voltage amplifier and feedback resistor.
“Adding the amplifier and resistor allows power to be very efficiently transferred across most of the three-foot range and despite the changing orientation of the receiving coil,” said graduate student Sid Assawaworrarit, lead author of the study. “This eliminates the need for automatic and continuous tuning of any aspect of the circuits.”
In an experiment, the team demonstrated successfully that an LED bulb attached to a receiving coil achieved uniform brightness as it moved up to three feet away from the source, without the need for any manual tuning.
“This is in contrast with conventional methods where high transfer efficiency can only be maintained by constantly tuning the frequency or the internal coupling parameters as the transfer distance or the relative orientation of the source and receiver units is varied,” the authors wrote in the June 14 online edition of Nature.
According to the Stanford researchers, if further developed to transfer a greater amount of electrical energy more efficiently, this type of wireless charging technology will not only potentially extend the range of electric vehicles, but can be applied in the more seamless charging of mobile devices and medical implants.