Adjustable power management could enable wireless charging of electric vehicles on the road

Drexel researchers helped demonstrate a more controllable system for wireless electric vehicle charging that could one day help enable on-road charging.

One of the biggest issues holding back the adoption of electric vehicles is the fear of being stuck with a dead battery and no charging stations nearby. In addition to the Biden administration’s recent push to install more charging stations across the country, tech developers are also tackling this “range anxiety” with the vision of ubiquitous wireless charging built right in. in the roads. A breakthrough by an international team of researchers, led by engineers at Drexel University, could help make this kind of built-in wireless charging a reality.

Their discovery, reported in the newspaper IEEE Transactions on Industrial Electronicsoffers a solution to one of the fundamental physical challenges facing all wireless charging technologies: misalignment.

While wireless charging has eliminated cable clutter and frustration with mismatched or faulty outlets, anyone who’s accidentally placed their phone on a slightly off-the-wall charger — and returned to find it drained — can attest to that. is not yet infallible.

Getting an electric vehicle to line up perfectly on a wireless charger can be an even more difficult task – misalignment leading to an equally unpleasant surprise. “In practice, misalignment between receiver and transmitter is unavoidable,” the team acknowledges in its report. But current wireless charging technology for electric vehicles is unable to adapt to the slightest lag without its function or efficiency suffering.

One of the biggest issues holding back the adoption of electric vehicles is the fear of being stuck with a dead battery and no charging stations nearby. In addition to the Biden administration’s recent push to install more charging stations across the country, tech developers are also tackling this “range anxiety” with the vision of ubiquitous, directly integrated wireless charging. to roads. A breakthrough by an international team of researchers, led by engineers at Drexel University, could help make this kind of built-in wireless charging a reality.

Their discovery, reported in the newspaper IEEE Transactions on Industrial Electronics, offers a solution to one of the fundamental physical challenges facing all wireless charging technologies: misalignment.

While wireless charging has eliminated cable clutter and the frustration of incompatible or faulty outlets, anyone who’s carelessly placed their phone on a charger can attest, it’s still not foolproof.

Getting an electric vehicle to line up perfectly on a wireless charger can be an even more difficult task – misalignment leading to an equally unpleasant surprise. “In practice, misalignment between receiver and transmitter is unavoidable,” the team acknowledges in its report. But current wireless charging technology for electric vehicles is unable to adapt to the slightest lag without its function or efficiency suffering.

The researchers, from Drexel’s College of Engineering and Jiao Tong University in Shanghai, Zhejiang University and Northwestern Polytechnic University, China, developed and tested a charging system versatile enough to adjust how it delivers an inductive load, so it can accommodate misalignment. and different battery charge levels.

“Creating a more forgiving system that can adapt to the realities of electric vehicle charging is an important step toward widespread adoption of wireless charging,” said Fei Lu, PhD, assistant professor at Drexel, who is one of the main researchers. “There is great potential for wireless charging to support dynamic charging of vehicles as they move down the road, but it is crucial that we overcome the alignment challenge first.”

Inductive charging works by using an electromagnetic field to transfer energy, similar to how wind or water might drive a turbine to generate electricity. An induction coil receives the electromagnetic “push” from the charger and transforms this vibration into energy that charges the device or vehicle battery.

But, like a misaligned turbine that misses all the force of the wind or water, inductive charging coils that are not properly coupled will not charge the battery effectively and – with sufficient misalignment – they may fail to energize. the whole charging process.

What the researchers found, however, is that with inductive charging, it’s actually possible to exert a bit more control over the torrent that transfers energy.

The team’s strategy differs from current wireless chargers, which can only adjust the voltage – the amount of charge – pushed into the system. Their hybrid method shows that adjusting the frequency of the field – how quickly or slowly voltage is transferred – produces a greater range with which to adjust misalignment or battery charge.

“Think of our wireless charging challenge like trying to fill a small glass of water under a running tap. It can be quite tricky because if you don’t hold it directly under the tap, a lot of water will miss in the glass,” Lu said. “And once it is almost full, the force of the jet will splash the water from the glass without it ever being filled to the brim. The key to our system is that it provides more control over the tap – or load power, so to speak – so it’s easier to direct more of the flow into the glass and slow it down when the glass is filling up.

To test their theory, the researchers produced a prototype of their system, built to the standards for wireless chargers for electric vehicles set by the Society of Automobile Engineers. It included an adjustable resistor, in order to simulate different levels of battery charge, and a moving platform that allowed the sender coil and charging coil to be pushed up to 100 millimeters out of alignment – which was about half the width of the charging surface.

They tested the system on relatively charged and uncharged battery states, in both well-aligned and misaligned conditions. By adjusting both the frequency and charging process voltage, the prototype was able to provide stable input power from 0 to 3.3 kilowatts, which is the standard charging range for plug-in electric vehicle charging. And across all four sets of conditions, the team was able to achieve almost 96% efficiency – on par with commercial wireless chargers and slightly below that of plug-in chargers.

“Being able to vary the voltage while maintaining power to the charging system means this process could be used to efficiently charge both near-dead batteries and those that just need a top-up,” Lu said. “It also allows for adjustments to the charging station when multiple cars are using it at once, so charging power remains constant for all of them.We see this as a critical step in making inductive charging more resilient to real-world conditions . »

The discovery could also allow electric vehicles to eliminate some of the power conversion hardware currently needed to handle DC wireless charging. This would reduce some of the weight and cost of the vehicle. The team plans to continue its efforts to improve wireless charging technology by adapting the system to other types of wireless charging circuits, to ensure compatibility with all electric vehicles.

In addition to Lu, Hua Zhang, PhD, assistant research professor at Drexel; Yao Wang and Amr Mostafa, PhD students at Drexel; Chong Zhu, PhD, assistant professor at Shanghai Jiao Tong University; Ningfei Jiao, PhD, research associate at Northwestern Polytechnical University; and Ying Mei, PhD student at Zhejiang University.

This article will be published in the October 2022 edition of IEEE Transactions on Industrial Electronics, it is available online here: https://ieeexplore.ieee.org/document/9583844

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