German luxury automaker BMW will work with with rival Daimler to refine and develop wireless inductive charging technology — and has already proven the technology feasible by using it to charge a collection of plug-in cars, including BMW’s ActiveE prototype electric car, its i3 production electric car and i8 plug-in hybrid.
That’s according to an official press release made yesterday in which BMW detailed the new technology cooperation between both companies and described some of its early tests into the technology.
Unlike conductive or tethered charging where there’s a physical connection between a car and the charging station, inductive charging works by transferring power electromagnetically between a charging coil embedded in the ground and a specially-designed receiver plate fitted to the underside of the car.
In operation, power flows from the charging station to the inductive primary coil fitted into the centre of a parking space or garage, inducing an electromagnetic field around the coil. The magnetic field from the first coil induces a current flow in the secondary coil on the underside of the car, charging the car’s battery pack from this point on using the usual on-board power electronics.
By carefully controlling the frequency of the alternating current to a very narrow band and matching the resonant frequency of the two coils, total system efficiency of the inductive charging system can peak at over 90 percent. This means less than ten percent of the energy which is enters the wireless charging system at the primary coil is lost due to inefficiencies, while 90 per cent of the energy put into the charging system makes its way to the car’s on-board power electronics.
The biggest challenge to keeping that efficiency high however is the way in which the car is parked over the top of the primary coil. Park a few inches off-axis, and efficiency drops.
In an attempt to combat that, both Toyota and Honda’s inductive charging prototypes have included semi-automated parking where the car positions itself over the inductive charging plate for maximum efficiency. BMW however, uses a different system. Instead of fully-automated parking, BMW’s current system uses WiFi between the charging pad and the car to coach the driver into the perfect parking space.
At the moment, BMW says the inductive charging system has been used to charge a selection of its cars at rates of 3.6 kilowatts, resulting in an empty-to-full charge of a BMW i8 in under three hours, and a BMW i3 recharge time of around eight hours.
In the future however, BMW says it hopes to double the power transmitted wirelessly to 7 kilowatts, halving charging times.
BMW says it wants to pursue wireless inductive charging for future models as it is first more convenient and more weather-resistant than conductive charging technologies. Its demonstration of wireless charging technology mirrors that of other automakers like Honda and Toyota who are also trying to develop and lead in the wireless charging sphere before any arbitrary standards have been set.
As for BMW’s partnership with rival Daimler, whose Mercedes-Benz B-Class Electric Drive competes directly with the all-electric i3? We suspect both automakers are keen to avoid the problems both experienced by the Combined Charge Standard (CCS) and be among the first automakers to codify and design a comprehensive wireless charging solution. CCS, a quick charge standard jointly developed by and supported by all German automakers, has only recently entered the marketplace and has a far lower penetration rate than the Japanese-designed CHAdeMO DC quick charge standard favoured by Asian automakers.
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