No hassle with incompatible plug systems, no struggle with thick and clumsy cables: Wireless charging holds the promise of a conventient charging process without complexity. Drivers just need to place their vehicle in alignment with a charging coil. In combination with two accordingly dimensioned capacitors, the (fixed and mobile) coils form a resonant antenna system for energy transmission. The closer the two coils are positioned against each other, the more efficient the energy transfer.
Researchers at the Fraunhofer IWES (Kassel, Germany), which deals with the technology of energy systems, have introduced a cost-effective approach for such systems. “We were utilising standard components available at mass markets”, explains Marco Jung, deputy head of the power converter department at Fraunhofer IWES. In addition, the researchers utilised coil systems that require fewer ferrite elements. The ferrite plates are used to shield the magnetic field. They are expensive and, due to their high content of iron oxide, heavy.
The system’s power electronic circuitry has been designed to achieve a high energy efficiency of 93 to 95% across the entire power range from 400W to 3.6 kW even at a relatively high coil distance of 20 cm, explains project manager René Marklein. “Comparable systems achieve such a high efficiency only at a lower distance which leads to limited usefulness for vehicles with high ground clearance.”
The charging system is integrated in the vehicle, containing all necessary electronics as well as various connector systems for the case that wireless charging infrastructure is not available. The Fraunhofer scientists designed it for maximum user flexibility, supporting single and three phase grid connection. It is also capable of managing not only the charging process, but also the other way: By discharging the battery to the power grid it can contribute to the stability of the grid and serve as energy storage in solar and wind-powered grids.
Typically, induction plates and coils are integrated in parking bays. Since they transfer