Researchers developing roads that charge your electric car while you're driving
Clemson University's International Center for Automotive Research (ICAR) in Greenville, S.C., has been testing stationary wireless vehicle charging and is now preparing to test mobile wireless recharging for vehicles.
Clemson's R&D project is backed in part by a multimillion-dollar grant from the U.S. Department of Energy (DOE), and is in collaboration with the Oak Ridge National Laboratory (ORNL), Toyota, Cisco and other companies.
The university's stationary wireless charging technology uses magnetic resonance to create a field between a ground charging coil and a copper coil embedded in a vehicle through which electricity can pass. Key to the technology is the Wi-Fi communications system, created by researchers at Oak Ridge that allows the ground and vehicle charging systems to talk to one another.
Stationary wireless vehicle charging is an emerging technology already commercialized by Evatran and Bosch. The two companies unveiled their PLUGLESS vehicle charging system at the 2014 Consumer Electronics Show in Las Vegas. The PLUGLESS charger is available for the Chevrolet Volt for $2,998 and the Nissan LEAF for $3,098.
Joachim Taiber, a Clemson professor of electrical and computer engineering, said there's a big difference between commercial wireless vehicle chargers and the ones his research team is testing. The main differences are between the transmission communications systems and the amount of power that can be transferred.
The Clemson ICAR has been able to transfer up to 250 kilowatts (a kilowatt is 1,000 watts).
Along with Cisco, ICAR has developed a Dedicated Short Range Communication (DSRC) technology that can support both stationary wireless charging and in-motion wireless charging with the same system architecture.
DSRC creates a vastly faster communication link between vehicles or roadway technology than say Wi-Fi, so that communications can be established even as a vehicle passes a wireless charger at high speeds.
Today, the National Highway Safety Administration is considering the DSRC protocol, which operates at 5.9 GHz, for mandatory use in vehicle-to-vehicle communication for crash avoidance. Essentially, cars will detect other cars or infrastructure with DSRC modules and automatically avoid a collision.
If every car were mandated to have the modules, a massive market could be created for using the communications protocol not only for crash avoidance, but also wireless charging, Taiber said.
Taiber, also the chief technology officer at the International Transportation Innovation Center, a 559-acre test bed in Greenville, said ICAR is planning to test the in-motion wireless charging with DSRC technology later this fall.
ICAR's first test of its wireless charging station demonstrated power transfer systems integrated into two different Toyota vehicle models. One of the vehicles was tested at a power transfer rate of 6.9 kilowatts and achieved an overall efficiency of greater than 85%.
Because of the high efficiency of the system, the difference in charge times between a wired charging system and a wireless charging system is "minor," Taiber said.
The idea behind dynamic wireless charging is to create a series of embedded highway stations that can incrementally recharge electric vehicles carrying mobile receivers as the vehicles drive by.
In the U.K., the government is expected to perform off-road trials of dynamic wireless charging that it acquired from researchers at North Carolina State University (NCSU).
The NCSU research suggests that vehicles driving on roadways with dynamic wireless charging stations could increase their driving range anywhere from 62 miles to about 310 miles.
"Currently, at peak efficiency, the new system can transmit energy at a rate of 0.5 kilowatts (kW). "Our goal is to move from 0.5 kW into the 50 kW range," Srdjan Lukic, an assistant professor of electrical engineering at NC State and senior author of a paper on the research, told Phys.org.
"That would make it more practical," Lukic added.
The U.S. wireless power transfer projects started in 2013 after the DOE created an $8.1 million grant for the research. The ORNL subcontracted with Clemson to develop the highway grid-side and vehicle-side communication system for wireless charging.
Taiber said the effectiveness of in-motion wireless charging depends on several things, including a vehicle's battery technology and how much energy it can absorb.
The research project will also test the use of ultracapacitors in cars that can store energy in an electric field, rather than in a chemical reaction, and then transfer it to the vehicle battery as needed.
"The power level we designed it for is up to 250 kilowatts. So you can push a lot of power through. Obviously, how much power [the vehicle] can absorb depends on the speed of the car," Taiber said.
For example, in urban settings, where vehicles may sit at intersections or traffic lights, the vehicles can absorb greater amounts of power, Taiber said. Conversely, vehicles traveling along high-speed highways would be able to absorb far lower amounts of power.
"We see great potential in understanding the technology of wireless charging to deliver value to our customers. In particular, we see the need to work more on dynamic wireless charging and to automate the charging process," Jae Lee, Toyota research and development manager, said in a statement.