Enabling electric cars to recharge themselves wirelessly

The technology could be scaled up to power electric cars as they drive over highways, robots on factory floors and drones hovering over rooftops.

It is no longer inconvenient to charge objects in motions, thanks to a technology developed by Stanford engineers. Engineers have taken a step forward towards making this concept practical to recharge electric cars as they speed along futuristic highways built to “refuel” vehicles wirelessly.

In the future, the system is expected to wirelessly recharge robots as they move around in warehouses and on factory floors—eliminating downtime and enabling robots to work almost around the clock.

Stanford electrical engineer Shanhui Fan said“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. 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.”

In their first breakthrough three years ago, the specialists built up a wireless charger that could transmit power even as the distance to the receiver changes. They did this by incorporating an amplifier and feedback resistor that permitted the system to automatically adjusts its operating frequency as the distance between the charger and the moving object changed. 

Be that as it may, that initial system wasn’t significant enough to be practical. The amplifier uses so much electricity internally to produce the necessary amplification impact that the system just transmitted 10% of the power moving through the system.

In this new study, scientists show how to boosts the system’s wireless-transmission efficiency to 92%.

Sid Assawaworrarit, a graduate student in his lab, said, “The key was to replace the original amplifier with a far more efficient “switch mode” amplifier. Such amplifiers aren’t new, but they are finicky and will only produce high-efficiency amplification under very precise conditions. It took years of tinkering, and additional theoretical work, to design a circuit configuration that worked.”

Stanford electrical engineer Shanhui Fan said, “There aren’t any fundamental obstacles to scaling up a system to transmit the tens or hundreds of kilowatts that a electric car would need. The system is more than fast enough to re-supply a speeding automobile. The wireless transmission takes only a few milliseconds—a tiny fraction of the time it would take a car moving at 70 miles an hour to cross a four-foot charging zone. The only limiting factor will be how fast the car’s batteries can absorb all the power.”

Assawaworrarit said, “The wireless chargers shouldn’t pose a health risk, because even ones that are powerful enough for cars would produce magnetic fields that are well within established safety guidelines. Indeed, the magnetic fields can transmit electricity through people without them feeling a thing.”

Fan said, “Though it could be many years before wireless chargers become embedded in highways, the opportunities for robots and even aerial drones are more immediate. It’s much less costly to embed chargers in floors or on rooftops than on long stretches of highway. Imagine a drone that could fly all day by swooping down occasionally and hovering around a roof for quick charges.”

Journal Reference:
  1. Sid Assawaworrarit, Robust and efficient wireless power transfer using a switch-mode implementation of a nonlinear parity–time symmetric circuit. DOI: 10.1038/s41928-020-0399-7

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