NC State University researchers have recently implemented what is being used in radios for decades in wireless power transfer (WPT) receivers – the ability of the receiver to keep track of the transmitter’s frequency if the differences are really small. This could ultimately impact electric vehicle wireless power transfer systems by making them more efficient and reliable.

“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 at NC State and co-author of a paper on the research.

For those who don’t know, WPT systems transmit significant amounts of energy by using tuned magnetic waves. If the frequency of the receiving end is tuned with the transmitter’s frequency, if they resonate with each other, then the transfer of energy is at its peak efficiency. Should there be slight differences in frequency between the two, then the efficiency drops and the current transmitted is not amplified (just like a broken musical instrument).

Lukic and Ph.D. student Zeljko Pantic’s innovation sits in additional electronics circuitry that they developed for the receiver to tune it with the transmitter. They did that by injecting small amounts of reactive power (those who used to stay “tuned” to their physics classes know what that is) into the receiving circuit just to maintain its original resonant frequency.

A second improvement is that, if the transmitter’s frequency changes (slightly), the receiver tunes itself to that frequency. The technique used in FM radios is called PLL (phase locked loop) – I don’t know what they used here, but my gut says it’s something similar to that.

Just a quick reminder: Nissan has recently said that it intends to make wireless charging a standard in their future electric cars. Other car manufacturers will also join the movement, and thus will make this technology just as common as fuel injection in gas  cars. For the moment, the efficiency of such devices is far from being perfect (and my guess is that it’ll never reach the good-old copper cable), but there’s a lot of room for improvement. Every engineer working in the field should praise Tesla for inventing it in the first place.

It’s must be a pride for these two fine Serbian engineers to follow their ancestor’s path for improving the wireless power transmission technologies… invented 120 years ago.

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