Comprehensive Design Approach for a Two-Stage Fixed-Frequency Contactless Energy Transfer System Based on the Extended First Harmonic Approximation

Resonant converters represent a suitable family of topologies that can handle the loose inductive coupling encountered in applications for contactless energy transfer while still providing high efficient operation. However, the analysis of resonant converters is in general cumbersome. On circuit level, a design procedure based on the extended first harmonic approximation of the multi-resonant LLCC converter with secondary side series compensation is presented in this paper. Together with a numerical model for the field distribution of core geometries with rotational symmetry a combined design procedure is discussed for the resonant tank. A high number of design parameters is included in this approach regarding the winding layout of the transmission coils such as number of turns, number of strands and strand diameter of thc litz wire, also taking into account the high frequency losses of the windings. The resulting two-stage system with the resonant converter working on a fixed-frequency was designed to be very tolerant against variations of the distance between the coils, at the same time achieving a very high efficiency for this kind of application.