Wireless charging - a more cost-effective approach

July 30, 2014 // By Christoph Hammerschmidt
The current in wireless charging for electric vehicles provides for inductor coils under the bottom of the vehicle; the corresponding charging coil typically is embedded in the ground. This concept has its disadvantages: Because of the large distance between of up to 15 cm between the coils, the size of the coils needs to be rather large. This translates into high material costs. In addition, objects or animals can enter the gap between the coils; cats for example like the slightly warmed charging area in the ground for a nap. Particularly problematic are metallic papers like chewing gum or cigarette packaging materials; exposed to the magnetic alternating field they can heat up and even catch fire.

Researchers from the Fraunhofer IISB institute for integrated systems and components therefore adopted a different approach: Within the project 'Energy Campus Nuremberg' they developed a system that allows charging the vehicle from the front side rather than from the bottom. The vehicle drives up to the charging coil, and since it can virtually close the gap in touching the charging coil with its receiver coil, the coils can be much smaller - 10 cm instead of 80 cm in the conventional approach. This makes the system more efficient and cost-effective, and it reduces the likelihood that objects can enter the space between the coils.

The waist-high charging column is made of plastic; it can fold away if a car hits it. The car even can drive over the column without being damaged. Multiple coils (vertically overlapping in the charging column and horizontally overlapping in in the car’s bumper behind the license plate) enable the charging process to be conducted successfully even in cases when the vehicle is not positioned exactly. The same holds true if the bumper does not have the height required; the vehicle can be higher or lower without causing a negative effect.

To keep the resistance of the cols under alternating voltages as low as possible, they devised a particular design for the coils: The coils consist again of multiple fine isolated coils. “The design of the coils is important since it determines the direction and intensity of the magnetic field”, explains Bernd Eckardt, manager of the department Vehicle Electronics at Fraunhofer IISB. Over time, the researchers succeeded in increasing the efficiency of the system; the current prototype reaches the 95% mark. “Thus, current electric vehicles can be charged in a couple of hours, for instance during the night”, Eckardt says. The goal is it now to further increase the charging power - in particular to align the system with the latest developments in battery technology. The