Engineers at Stanford University in california have taken a wireless charging system for moving electric vehicles out of the lab and adapted it for real world use.
Three years ago, Stanford electrical engineer Shanhui Fan and Sid Assawaworrarit, a graduate student in his lab, built the first system that could wirelessly recharge objects in motion regardless of the distance using a technique from quantum machanics. However, this only had a 10 per cent power transfer rate.Now the two researchers have developed a switched mode amplifier and feedback circuit that can deliver 92 per cent transfer efficiency.
“This is a significant step toward a practical and efficient system for wirelessly re-charging automobiles and robots, even when they are moving high speeds,” said Fan. “We would have to scale up the power to recharge a moving car, but I don’t think that’s a serious roadblock. For re-charging robots, we’re already within the range of practical usefulness.”
The prototype can wirelessly transmit 10W of electricity to a moving receiver over a distance of up to 62cm, but there aren’t any fundamental obstacles to scaling up a system to transmit the tens or hundreds of kilowatts that a car would need, says Fan, and the transmission takes only a few milliseconds. The only limiting factor will be how fast the car’s batteries, or a supercapacitor, can absorb the power.
The design uses a switch-mode amplifier with current-sensing feedback in a parity–time symmetric circuit. The parity–time symmetry guarantees that the effective load impedance on the switch-mode amplifier remains constant, which allows the amplifier maintains high efficiency despite variation of the transfer distance.