Development of a Wireless Power Supply System for an E-Bike

A wireless power transfer system for an electric bicycle was investigated in this study. Loosely coupled transmitter and receiver coils that are designed for an installation on a rack and a bike wheel were developed. Achieving required mutual inductance with compact size and light weight coils was the goal of the system design. To achieve the requirements, the transmitter and receiver coils were wound in a ferrite pot-core that increases coils' self-inductances and confines magnetic flux to prevent coupling with a bike wheel and a rack. Using finite element analysis, the dependence of the quality factor and self-inductance of a coil design methodology using the ferrite pot-core was studied in this paper. It was found that eddy-current loss of coils wound in a pot-core increased highly near the air-gap. To achieve a high quality factor, coil should be located as deep inside of the pot-core. On the other hand, coils' self-inductances decreased while coils were moved away from the air-gap. Also, mathematical analysis of a series-parallel compensated wireless power transfer system was studied. Stability margin, efficiency, and induced voltage were considered to optimize the load resistance. The proposed system was evaluated using an experimental test-bed. Measured coil-to-coil efficiency of the developed system was over 90 % and the overall efficiency was 73.2 % at its rated operation.