Contactless battery charger with high relative separation distance and improved efficiency

This paper presents the analysis and the design of a contactless energy transfer system to be used as a battery charger, for an electronic portable device. The separation distance between transmitter and receiver is of the same order as the coils dimensions, leading to a low coupling factor and imposing, therefore, a coreless transformer. The geometrical parameters of diverse transformer coils configurations were calculated in order to obtain the one that shows the higher magnetic coupling coefficient. The compensation system is composed by a series resonant converter working slightly above resonance, which is equivalent to an LLC resonant converter, when supplying the contactless loosely coupled transformer. The theoretical analysis is based in the development of a model that permits to obtain a closed set of equations enabling the definition of the output regulation characteristics. Simulated and experimental results were obtained to verify the accuracy of the theoretical study and also the circuit performance for each transformer configuration.