Researchers at Oak Ridge National Laboratory used these coils to generate magnetic fields to wirelessly charge electric vehicles.
Scientists at Oak Ridge National Laboratory (ORNL) in Tennessee have developed a wireless charging technology. They say the technology can fully charge an average electric car in an hour. That's a six-fold power boost over a similar wireless charging system they announced in 2016. They report that this plug-in electric vehicle charging technology is currently being improved for commercial applications such as delivery trucks.
Burak Ozpineci, head of Oak Ridge's Power Electronics and Power Machinery Group, said the team isn't done yet. He said they are working toward a larger goal set by the U.S. Department of Energy -- to create a series of fast, safe and simple electric vehicle charging systems. This will "accelerate the adoption of electric vehicles in the United States," according to the DOE's 2016 directive.
Their idea is to triple the power throughput of existing systems, bringing the total charging time of a drained EV battery to less than 15 minutes. And to charge an electric car, there's no need to plug anything into the car or do anything other than drive it to a wireless charging pad embedded in concrete.
The DOE directive doesn't say whether the systems should be wired or wireless, Ozpineci said. But he added, "Our expertise is in wireless. So we said, we're going to do the wireless part."
Current artist concept drawings of electric car charging pumps resemble car gas stations, but emit electrons instead of oil. And wireless charging for electric vehicles may represent more than just a new source of vehicle fuel. Like the wireless internet revolution 20 to 30 years ago, wireless power for electric vehicles may not just change the source of power for the car. Some futurists believe wireless power is playing a major role in the rise of "smart cities" and the demise of gas stations.
Photo credit: Genevieve Martin/ORNL/DoE
These ORNL-designed wireless coils and power electronics can safely transmit large amounts of electrical energy through the air with 97 percent efficiency.
The two key elements involved in their 97 percent efficient wireless charging technology, which can output 120 kilowatts of power, are the materials they use and the coils that transmit and receive electricity, Ozpineci said. They presented details of the technology at IEEE's Energy Conversion Congress and Exposition in September. This article from them will soon be published on the IEEE Xplore database.
Transmitting wireless power from the ground unit to the power receiving unit in the electric vehicle (with an air gap of about 6 inches between the two) means rapidly oscillating the electric and magnetic fields in the ground coil and the receiving coil in the electric vehicle cause similar behavior. In practical terms, that means delivering 120 kilowatts of power through an oscillating current at about 22,000 cycles per second, or 22 kilohertz, Ozpineci said.
"The problem is usually we have silicon devices, and when we get to higher power levels, you can't run them at higher switching frequencies," he said. "At 10 kWh, you can switch to 20 kHz. But When you get to 100 kilowatts and beyond, you have to lower the switching frequency — because of thermal issues, device response issues, a lot of things.â€
Photo credit: Genevieve Martin/ORNL/DoE
The coil outputs 120 kilowatts of power through an oscillating current of approximately 22 kilohertz.
However, transferring higher power with high efficiency requires higher switching frequencies. So this effectively means both replacing the silicon with the more reliable (and more expensive) silicon carbide and strengthening the coils on the sending and receiving ends of the power exchange.
Tesla's Model 3 also uses silicon carbide electronics, Ozpineci said. Therefore, the reliance on materials of Oak Ridge's technology is not unprecedented in electric vehicle systems. On the other hand, they admit that their 100-pound (45-kilogram) coil needs some refinement and optimization before it can move to the design stage for commercial production.
They must then further innovate the design to triple the power to reach the Department of Energy's 350 to 400 kilowatt target. Ozpineci said that work is in progress, but he suspects that there must be multiple power modules in any wireless supercharger of 350 kilowatts or more.
Photo credit: Genevieve Martin/ORNL/DoE
Power electronics that manage current flow between the constituent components of a new wireless charging system developed by ORNL.
"We're able to use a single power module," he said of the current 120-kilowatt unit. "We're at or near the limit of these power modules. To do things beyond the limit, we either need to parallel these modules or we need to Put two inverters in parallel. When you do that, you have more challenges running these things in sync.â€
Ozpineci said his team is also working on a feasibility study for a so-called dynamic wireless charging system for electric vehicles. The Dynamic Wireless Charging System automatically charges electric vehicles in motion using wireless charging pads installed under the road.
He said: "Many groups around the world are looking at it, but most people are thinking about reducing power. Like 20 kilowatts. But we don't limit ourselves to 20 kilowatts. Do we need 100 kilowatts? Do we need 120 kilowatts? Need more High power? No matter what we get, the DOE will likely fund demonstration projects.â€
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