Wireless Charging: EV Power Via Slot-Car Technology

LONDON – As the drive to encourage electric-vehicle ownership gathers momentum, so does the desire to install automated recharging systems such as devices built into roads that top up batteries as the EVs drive over them.

Dynamic inductive charging technology has been tested in a range of scenarios globally. One system now is operating on a live transport route, on roads in two towns in South Korea.

High installation costs coupled with the relatively slow uptake of EVs are the main factors hindering wider installation of this technology, despite proof of its practicality and functionality.

But industry experts believe technological development in the field is so fast-moving that in-motion charging will be commonplace within the next five to 10 years.

Indeed, California-based Lucid Motors recently unveiled its luxury-level Air EV, fitted with inductive charging that enables battery range of up to 400 miles (240 km). Another California firm, Faraday Future, has launched the FF91, an electric SUV with a 378-mile (609-miles) range that is compatible with wireless charging stations.

Burak Ozpineci, group leader of the power-electronics and electric-machinery group of the National Transportation Research Center at the U.S. government’s Oak Ridge National Laboratory, is confident in the future of wireless charging. “In a few years, drivers of traditional (gasoline powered) cars will be viewed by society in the same way as smokers,” he says.

Utility companies will drive wireless charging, says Mashrur Chowdhury, a professor of transportation at the International Center for Automotive Research at Clemson University in. “It will all depend on how many electric vehicles we see. If we see gas prices going up and governments interested in investing more in alternative energy, (then) that will motivate the deployment” of wireless charging.

“Within five years I think we will see it in place in many areas,” he says. “When people see these roads in cities it will prompt more people to buy electric cars. It’s a 2-way street.”

Batteries will need to be cheaper and more effective to achieve this. Batteries, which currently account for up to 50% of the price of an EV, have proved cost-prohibitive for many drivers wishing to switch from traditional vehicles. Most existing EV batteries provide limited driving distance between charges and are a major source of the weight auto engineers are trying to reduce.

The electromagnetic technology involved in dynamic inductive charging is the same principle as the Qi wireless charging system that powers a smartphone. This could remove storage requirements for the battery, reducing both its weight and cost.

South Korea switched on its first wireless road in 2013 for its online electric vehicle (OLEV) bus service and has been expanding its coverage ever since.

Researchers at the Korea Advanced Institute of Science and Technology developed the system based on shaped-magnetic-field-in resonance technology designed for autos.

Electric cables installed under the road are used to generate electromagnetic fields that are picked up by a coil inside the vehicle’s device and converted into electricity. The receiving equipment can be up to 6.7 ins. (170 cm) above the road’s surface.

The power cable installed under the road surface can generate a 20-kHz magnetic field when the cable draws electricity from the power converter, which already has received electricity from the grid at a typical industrial level of 3-phase 440V. The converter delivers electricity to the battery.

The pickup coils fitted to the underside of the vehicle are tuned to 20-kHz-resonant frequency and designed to have maximum exposure to the generated magnetic field, which has an optimized shape to prevent leakage outside the required area.

A powered track consists of various component segments of different cable lengths according to the road type, expected vehicle speeds and vulnerability to traffic jams. For example, a short section just the length of a bus can be installed at pickup and set-down points.

During a demonstration in Seoul, just 17% of the 1.3-mile. (2.2-km) route was powered in three sections, but this generated sufficient power to operate an OLEV bus.

Wireless-charging systems power a bus service between the train station in Gumi and the capital city’s In-dong district; a bus route in the City of Sejong; and the shuttle-bus service around the KAIST campus.

Plans are under way to integrate wireless charging into a new urban development around the new Beijing International Airport. And a memorandum of understanding has been signed with the municipality of Medellin, Colombia, for OLEV buses.

Dong-Ho Cho, who led the KAIST team, says: “OLEV buses will greatly contribute to decreasing the consumption of fossil energy by achieving a fuel cost reduction of 38% compared to their diesel counterparts and 33% compared to their (compressed-natural-gas) counterparts.”

Canada-based manufacturer Bombardier’s PRIMOVE e-mobility team has performed a series of tests with a dynamically charged truck at a construction site in Mannheim, Germany. The 32.8-ft.- (10-m) -long vehicle, weighing 10 tons, was inductively supplied with up to 200kW of power using four 65-ft. (20-m) -long charging segments of underground cable.

“We are technically ready to install the technology in ‘real life,’” a PRIMOVE spokesman says.

In Utrecht, Netherlands, and Milton Keynes, U.K., buses are able to charge wirelessly at bus stops with static pads in the road connecting remotely to the underside of the vehicles.

“The wireless charging allows the buses to run throughout the day, enabling electric buses to do everything a diesel bus can do,” a spokesman for Milton Keynes Council says. “The buses will remove 5 tons of particulates and noxious tailpipe emissions from Milton Keynes’s streets each year. Approximately 270 tons of carbon-dioxide will be removed from the atmosphere.”

In the U.S., the Evatran Plugless charging system, compatible with the Chevrolet Volt, Nissan Leaf, Cadillac ELR and Tesla Model S EVs, is being introduced in private car parks allowing motorists to drive over a pad embedded in the ground and leave the vehicle to charge wirelessly.

“Magnetic resonance pads in the road that sync with pads on the underside of the vehicle will be readily available in three to four years,” predicts Prajyot Sathe, industry manager for powertrains and electric vehicles at business analyst Frost & Sullivan.

But he admits the technology is expensive, with the dynamic application estimated to cost $1 million per 0.6 mile (1 km), including underground cable and pad installation, resurfacing work and pads on vehicles.

“Wireless road technology would only come into the picture when we get a bigger market overall for electric vehicles,” Sathe says. “Inductive charging will only be in premium vehicles initially. For mass-market vehicles it’s very unlikely in the short term, but after five to seven years there will be more mass-market applications.”