Reliability boost for wireless power transfer

Posted by Kate Taylor

Electric vehicles could soon be charged wirelessly, thanks to a new way of fine-tuning wireless power transfer (WPT) receivers that makes them more efficient and functional.

While it's been known for some time that it's possible to transmit power wirelessly by using magnetic resonance, it's a hit-and-miss procedure, as even minor changes in how the receiver is tuned can result in faulty power transmission.

But a new prototype developed at North Carolina State can retune receivers automatically and precisely.

"We're optimistic that this technology moves us one step closer to realizing functional WPT systems that can be used in real-world circumstances," says Dr Srdjan Lukic, an assistant professor of electrical and computer engineering.

WPT systems transmit magnetic waves on a specific frequency, which interact with a coil in the receiver to induce an electric current. If the coil is tuned so that its resonant frequency matches the frequency of the magnetic waves, the current it produces is amplified.

However, if the receiver and the transmitter are out of tune, the system becomes inefficient and doesn't transfer nearly enough power. The receiver coil still picks up a trace amount of current, but it isn't amplified.

And the tuning is particularly sensitive, with factors such as temperature or proximity to other magnetic objects having a potentially devastating effect.

But the NC State team'sprototype incorporates additional circuitry into the receiver. This injects small amounts of reactive power into the receiver coil as needed to maintain its original resonant frequency; and, if the transmitter's tuning changes, can read the trace amount of current being transmitted and adjust the receiver's tuning accordingly.

"Because we are using electronics to inject reactive power into the receiver coil, we can be extremely precise when tuning the receiver," says Lukic.

"The next step is to try incorporating this work into technology that can be used to wirelessly charge electric vehicles."