Electric Avenues: Smart Roads Serve as Off-Board EV Range-Extenders - Technologue
Exploring the potential of dynamic wireless charging
The end of range anxiety? The key to lighter, more affordable electric cars? An impossibly expensive infrastructural pipe dream? Wireless EV charging through the road might prove to be all of the above, but on a stormy day in May, it also proved to be something else: technically feasible. On that day, at a 100-meter-long demonstration track located on a former French Army proving ground near Paris, two electrified Renault Kangoo vans each managed to draw 20 kW of electricity from inductive charging pads in the road while traveling at 65 mph—that's enough juice to cover propulsion and climate control loads while lightly charging the batteries. (At lower speeds, there's more charging.)
Wireless and telecom giant Qualcomm developed the technology based on its Halo static inductive charging system—which works when a vehicle is parked. Halo mounts laptop-size pads to the vehicle undercarriage and floor. The system steps grid power up to 800-plus volts DC. When the pads align, the system establishes an AC magnetic field alternating at 85 kilohertz. The vehicle side then converts this back to DC battery voltage (often 400 volts). The space between the pads is like a weak microwave oven, so the static systems feature object detection, shutting off if Fluffy slinks under the car or if something metal blows onto the pad. This is not future fantasy; this system is an expected option on the next-generation plug-in hybrid Mercedes-Benz S-Class.
Inductive charging rates can be tailored to specific applications—3.7 kW for PHEVs all the way up to 250 kW for large buses. Efficiency of the energy transferred across the pads is above 90 percent; additional system losses occur in the voltage conversions (just as with wired chargers), and there are more of these on the dynamic system.
Dynamic wireless charging works the same way except with a vehicle in motion and zillions of the floor pads centered in the roadway lanes. Qualcomm's demo roadway features four independently powered 25-meter "stubs" consisting of 14 base-array network (BAN) blocks coupled magnetically into a backbone cable. Communications gear verifies vehicle identification for billing, and then the BAN blocks energize sequentially, switching on within 3 milliseconds of vehicle detection and switching off immediately after the vehicle passes. The demo roadway can deliver 20 kW to two vehicles traveling at highway speeds, provided they're about 25 meters apart and centered in the lane within an 8.0-inch span. The demo track could conceivably charge additional closer-spaced vehicles but at a lower rate so as not to overtax any one stub. The demo Kangoos each carry two 10-kW receiver pads, one each at the front and rear, operating across a 6.8-inch gap to the base plates.
This demo project targeted a total charging system efficiency of 80 percent at speed and is reportedly close to achieving that goal. But the team also acknowledges that the effective working gap between the pads and vehicle undercarriage will need to be much greater than 6.8 inches to allow for an asphalt layer above the pads and typical SUV/CUV ground clearances of 7 or 8 inches. (Mechanically lowering a vehicle's receiver pads is not an option due to the risk of striking an object.)
Qualcomm hopes to broadly license its static charger technology so that a large fleet of inductively chargeable vehicles might spur infrastructure investment. Strategically fitting certain arterial urban roadways and inter-urban interstate stretches could allow EV batteries to shrink without inciting range anxiety.
What'll it cost? Less than $1,000 for the vehicle gear. Roadway cost predictions have not been shared yet, though tolling and energy billing will offset some costs. I'm not holding my breath for imminent rollout of inductive roadways, but the tech sure seems appropriate for a mostly ride-shared, fully autonomous future; this is the easiest, most efficient way for robo-EVs to recharge themselves. Personally, I'd sooner invest in electric avenues than a nationwide network of hydrogen stations.