Stanford Tackles Wireless EV Charging
Originally published on Gas2.
Some of you are going to read this and say, “Ho hum. Another useless story about some silly lab experiment that has no relevance to the real world.” And you could be right. There may be nothing here. Then again, figuring out how to keep an electric car fully charged wirelessly while driving could be a huge deal someday — even if that day is fairly far off.
Researchers at Stanford’s Precourt Institute For Energy have figured out how to solve one of the most vexing problems associated with wireless charging — adjusting automatically for variations in the distance between a wireless charging source and the receiver built into a car while one is in motion.
Under normal circumstances, the amount of energy transferred varies a great deal as that distance varies. But Stanford professor Shanhui Fan and graduate student Sid Assawaworrarit figured out how to automate that process. By eliminating the radio frequency component of the wireless transmitter and replacing it with a commercially available voltage amplifier and feedback resistor, the pair was able to create a device that automatically determines the correct frequency needed for different distances.
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“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,” says Assawaworrarit, the lead author of the study. “This eliminates the need for automatic and continuous tuning of any aspect of the circuits.”
“In theory, one could drive for an unlimited amount of time without having to stop to recharge,” Fan explains. “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.”
Here’s the part that may have some jeering. So far, the experiment has only been successful at transmitting one milliwatt of power. “We still need to significantly increase the amount of electricity being transferred to charge electric cars, but we may not need to push the distance too much more,” says professor Fan. The amplifier the researchers used is only 10% efficient, but high-performance amplifiers that are up to 90% efficient are available.
The researchers see other possibilities for wireless charging systems built into roadways. In addition to charging passing cars, they could improve autonomous driving controls that rely on GPS signals. GPS is only accurate down to about 35 feet. The information conveyed to the car’s guidance system from a wireless charging system would be accurate to a few millimeters.
The technology has other potential benefits. “In addition to advancing the wireless charging of vehicles and personal devices like cellphones, our new technology may untether robotics in manufacturing, which also are on the move,” says Fan. “We can rethink how to deliver electricity not only to our cars, but to smaller devices on or in our bodies. For anything that could benefit from dynamic, wireless charging, this is potentially very important.”
For more on how the new system works, watch the YouTube video below.
Source: Stanford University
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