Professor John Haddock and graduate student Oscar Moncada examine a slab of concrete pavement they tested to handle heavy truckloads with wireless power-transfer technology installed below the surface. The machine behind them is designed to imitate those loads by repeatedly passing half a loaded semi-truck axle across the concrete slab. (Image: Consensus Digital Media)

Purdue University engineers and the Indiana Department of Transportation (INDOT) are working to make it possible for electric vehicles ranging from tractor-trailers to passenger cars to wirelessly charge while driving on highways.

Construction is in progress on a quarter-mile test bed on U.S. Highway 231/U.S. Highway 52 in West Lafayette that the team will use for testing how well a patent-pending system designed by Purdue engineers can provide power to a heavy-duty electric truck traveling at highway speeds.

An electric truck provided by Indiana-based company Cummins Inc. will drive over the test bed as part of a pilot program planned to start next year. The hope is to electrify a section of an Indiana interstate in the next four to five years.

A few other states and countries have also begun testing roads that wirelessly charge EVs. But making this possible for highways — and heavy-duty trucks in particular — is a unique challenge. Because vehicles travel so much faster on highways than city roads, they need to be charged at higher power levels. So, this wireless charging system is intended to work at much higher power levels than what has been demonstrated in this country so far. By accommodating the higher power needs for heavy-duty vehicles, the design is also able to support the lower power needs of other vehicle classes.

Building electrified highways with heavy-duty trucks in mind would maximize greenhouse gas reductions and the economic feasibility of developing infrastructure for EVs. Heavy-duty trucks are one of the biggest sources of greenhouse gas emissions for the U.S. transportation sector because they make up a large portion of interstate traffic. Compared to passenger cars, these trucks also need a lot more fuel.

“The so-called ‘middle mile’ of the supply chain, which refers to all the travel heavy-duty trucks must do to carry goods from one major location to another, is the most challenging part of the transportation sector to decarbonize,” said Nadia Gkritza, a Purdue professor of civil engineering and agricultural and biological engineering.

But if electric heavy-duty trucks could charge or maintain their state-of-charge using highways, their batteries could be smaller in size and they could carry more cargo, significantly reducing the costs of using EVs for freight transportation. Since trucking contributes more to U.S. gross domestic product compared to other modes of freight transportation, lowering costs for heavy-duty electric trucks could help attract more investment into electrifying highways that all vehicle classes would share.

“We’re developing a system that has the power to charge semi tractor-trailers as they move 65 miles per hour down the road,” said John Haddock, a professor in Purdue’s Lyles School of Civil Engineering.

The technology Purdue is developing would enable highway pavement to provide power to EVs similarly to how newer smartphones use magnetic fields to wirelessly charge when placed on a pad. “If you have a cellphone and you place it on a charger, a magnetic field from the charger couples power into the phone. We’re doing something similar. The only thing that’s different is the power levels are higher and you’re going out across a large distance from the roadway to the vehicle,” said Steve Pekarek, Purdue’s Edmund O. Schweitzer, III Professor of Electrical and Computer Engineering. “This is a simple solution. There are complicated parts of it, and that we leave to the vehicle manufacturers.”

In the Purdue wireless charging system, transmitter coils would be installed in specially dedicated lanes underneath normal concrete pavement and send power to receiver coils attached to the underside of a vehicle.

The Purdue-designed coils accommodate a wider power range than existing wireless EV charging systems — larger vehicles wouldn’t need multiple low-power receiver coils on the trailer to charge from the road. Instead, a single receiver coil assembly is placed under the tractor, greatly simplifying the overall system.

These transmitter coils are designed to work within concrete pavement, which makes up 20 percent of the U.S. interstate system. Other coil designs have only been developed for use in asphalt pavement.

The team has done lab tests verifying the electromagnetic performance of the bare transmitter coils and the receiver coils. They have also completed testing how well 20-foot-long sections of concrete and asphalt could handle heavy loads with the transmitter coils embedded. They imitated truck traffic by having a machine repeatedly drive a loaded one-half semi axle over the pavements.

“We don’t envision 100 percent of the roads being electrified,” Gkritza said. “But we see the potential for dynamic wireless power pavement technology as complementary to an expanding network of EV charging stations. We feel it would be useful in areas where charging stations are scarce in underserved communities, even supporting transit routes where initial charging at the depots and terminal stations might not be enough and there might need to be some charging in between the routes.”

The researchers anticipate that it may be 20 to 30 years before EVs can receive the full power they need while driving at highway speeds. It is up to EV manufacturers to decide whether to incorporate receiver coils into their vehicles.

“The technical obstacles that we need to overcome are not insurmountable. Those can be overcome with proper design,” said Dionysios Aliprantis, a Purdue electrical and computer engineering professor. The team hopes that the results of their experiments could help convince the industry that electrified highways could work.

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