A New Magnetic Structure of Unipolar Rectangular Coils in WPT Systems to Minimize the Ferrite Volume While Maintaining Maximum Coupling

Abstract

In the wireless power transfer system, the transmission efficiency and power transfer capability depend on the coupling coefficient ( k). Usually, the coupling of the air-core unipolar coil system is weak. For improving k, the ferrite core is used. In traditional ferrite arrangement, the ferrite core size is kept approximately equal to the coil dimensions, which increases the overall weight and volume of the system. This brief proposes a novel and simple ferrite arrangement of unipolar rectangular coils, which maintains the maximum achievable k and minimizes the volume of ferrite used. Pythagoras' theorem is used to calculate the position and length of the ferrite bars. Furthermore, various possible ferrite arrangements are studied and compared with the proposed ferrite arrangement (PFA). The proposed arrangement saves 81.24% volume of the ferrite used with a decrement of only 6.93% in k (at the 150-mm air gap) over the traditional arrangement. Finally, a prototype of the PFA is developed, and the results are verified.