Stanford Announces Electric Car Wireless Charging Breakthrough


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.

wireless charging system Stanford

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.

“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

About the Author

I have been a car nut since the days when Rob Walker and Henry N. Manney, III graced the pages of Road & Track. Today, I use my trusty Miata for TSD rallies and occasional track days at Lime Rock and Watkins Glen. If it moves on wheels, I'm interested in it. Please follow me on Google + and Twitter.
  • dogphlap dogphlap

    The text explanation made hardly any sense to me (however it was atchieved) but I think I got the gist i.e. the power transfer is kept constant as the distance from transmit coil to receiver coil is varied over a distance of up to one metre.
    I don’t see how this is a breakthrough for wireless charging for cars, in general keeping the power transfer constant is not of great importance. Mostly all you want is to maximise the power transfer, whatever the separation and with minimum loss.
    As to the power transfer being only 1mW, that blue/white LED is consuming at least 50mW but either way there are no claims about the maximum level of power that could be transferred so I see no reason to criticise that aspect of the demonstration.

    • Steve Hanley

      Well, the folks at Stanford think its a big deal and since they are a lot smarter than me, I going with that!

      Personally, I think any idea that involves special equipment buried in roads is DOA, but my role is to inform, not to judge.

      • Joe Viocoe

        Well, its a big deal for Stanford whenever a graduate student invents something interesting. Its still a big deal for them even if the technology is ultimately never getting out the lab.

        What it certainly is not, is a “breakthrough”. They don’t use that word, so neither should the headline. It falsely implies that it was an important piece to the puzzle that has been solved. Unfortunately, it isn’t really a solution to any problem that engineers were actually worried about.

        The economics of dynamic in-road charging are seriously flawed, worse than hydrogen, and only somewhat better than solar freakin roadways.

        But they are right, there are other applications for this technology, even if not for EVs, so good on them.

  • Jim Smith

    you have to start somewhere