Although electric vehicles (EVs) have posted only modest sales figures as yet, recharging access, the other side of the electric car equation, is burgeoning. Already today 64,000 plug-in EV charging stations operate worldwide and should number some 200,000 by 2020, according to market analyst Navigant Research. And during the next decade, revenue from the sales of plug-in charging station equipment should grow tenfold, rising to $5.8 billion, it predicts.
But despite the growth of EV recharging access, many EV advocates point to no-hands, wireless charging capability as the next step toward truly widespread adoption of electric cars, especially in the U.S. Just parking above a charging pad in your garage or the parking lot seems a no-brainer compared with fumbling with cables and plugs.
Starting with Nikola Tesla’s striking demonstrations of WPT (wireless power transfer) a century ago, inductive charging has become familiar in electric toothbrushes and smart phones. For cars, EV inductive charging involves an induction coil in a base station to produce an alternating electromagnetic field, and an onboard induction coil that draws power from the field and converts it back into current to charge the battery.
Wireless charges ahead
Lately, it seems that things may be starting to fall into place for the cordless technology. An SAE International global task force working to update a standard (J2954) on wireless charging recently agreed to a common power transfer frequency (85 kHz).
Meanwhile, reports from the recent International Electric Vehicle Symposium in Barcelona signal bright prospects for wireless charging. Qualcomm’s Britain-based Halo division, which for the past two years has been working on an 85-kHz WTP technology developed at the University of Auckland, is aiming to outfit several carmakers with cordless capabilities by the end of 2016.
Next year, said Anthony Thomson, Qualcomm Vice President for Business Development and Marketing, the company will test out its 20-kW charging technology by wirelessly powering the electric track-safety vehicles at the FIA Formula E all-electric racing series events in places such as Beijing, Buenos Aires, Los Angeles, Miami, Monte Carlo, and London. In subsequent seasons, the racecars themselves will be charged without cables.
Other reports from the EVS show indicate that Nissan will introduce late next year an Infiniti LE (a Leaf cousin) that can charge wirelessly using a pad system supplied by WiTricity, which is licensing technology developed at MIT.
Inductive charging of EVs has “a promising future,” concluded a recent study of wireless EV charging conducted by Volvo and Flanders’ Drive, the Belgian automotive research center. The project, which was partly funded by the Flemish government, included Bombardier Transportation and the coachbuilder Van Hool. Volvo supplied a C30 Electric sedan.
“Inductive charging has great potential,” said Lennart Stegland, Vice President, Volvo Electric Propulsion System. “Cordless technology is a comfortable and effective way to conveniently transfer energy. The study also indicates that it is safe.” Sensible government regulations are needed to speed installation, Volvo said in a statement.
As the initial public investments in EV charging infrastructure have waned, the numerous suppliers that emerged onto the market early on are starting to consolidate. Industry teams have formed in the last few years. WiTricity linked up with Delphi and Toyota. Evatran and Yazaki are working together, as are Evatran and Bosch, and Siemens and BMW. Oak Ridge National Laboratory and Clemson University have joined up. Big players such as GE and Denso have their own collaborations.
Charging on the go
Although wireless charging is in its infancy, there is increasing talk of taking the technology to the next level: to charge cars wirelessly as they travel on the road. The Qualcomm/Halo and the University of Auckland group have long spoken about one day linking cities with “charging lanes” so drivers can just drive, picking up power en route.
So-called dynamic wireless charging is under evaluation at a quarter-mile stretch of road with two buried charging lines at Volvo’s Swedish test facility. Last year Volvo and the Swedish power company Alstom constructed the track. They have tested it with a diesel truck, and plan to try electric cars as well.
In Gumi, South Korea, the Korea Advanced Institute of Science and Technology is running a dozen buses on a 24-km (15-mi) city route over roads that recharge the batteries while in motion. The buses receive power across a 170-mm (6.70-in) air gap via a 20-kHz signal that transmits 100 kW with 85% efficiency. The system employs what the developers call “shaped magnetic field in resonance” technology.
The Korean system uses large, powerful transmitter coils. But this approach produces a strong, somewhat less precise field that may possibly couple to the frame of a car or other metal objects that pass through the field, said Srdjan Lukic, Assistant Professor of Electrical Engineering at North Carolina State University in Raleigh. The strong fields needed for sufficient power transfer increase the chance of leaks, raising concerns about safety and efficiency loss.
The Auckland approach, in contrast, uses smaller transmitter coils to address safety and efficiency concerns, Lukic said. But this system requires a large numbers of smaller transmitters to fully cover a section of the roadway, potentially adding substantial cost and complexity. This method, he noted, must precisely detect the vehicle’s position.
Lukic and NCSU doctoral students Zeljko Pantic and Kibok Lee have developed a new method that “solves the problem by taking the best from both of those approaches,” Lukic said. The system uses a series of segmented source (transmitter) coils in the roadway, each of which broadcasts a low-level electromagnetic field. They then are all connected in parallel so they draw the same amount of current.”
The onboard receiver coil is the same size as the transmitter coils so that at a specific frequency they resonate strongly to transfer energy more efficiently, he explained. Most of the time, however, the receiver is slightly detuned so it receives poorly. It resonates and receives well only when the vehicle nears the transmitter coils. Fast-acting reactive circuitry achieves resonance to boost power transfer by 400% as the car drives by. The current drops off when the receiver coil passes out of the range.
Lukic and his team have developed a 0.5-kW benchtop prototype and are now working to scale up the system “to around 50 kW.”
NCSU simulations indicate that an electric avenue with only 3% of the roadway electrified in urban areas and 10% on highways could extend the range of an EV fitted with a small, affordable battery—“something between a Prius and full electric car”—from 30 mi (50 km) to 300 mi (500 km).