Design of the resonant converter for the contactless inductive charging system

Inductively coupled power transfer (ICPT) technology is a kind of advanced charging mode which can transfer the power all weather, safely and high efficient. It has great prospect in numerous applications. However, for frequency control resonant converter with constant coupling coefficient, because of compensation circuit adopts and load change, multi-resonant can be generated, infecting system power transfer and making system unstable. Therefore, establish state equations and transfer function by mutual model, analyze the reason of multi-resonant generating, determine the load boundary condition which adopt series-parallel compensation structure. Then the variable-step frequency control method is proposed in this paper which have the advantages of simple, reliable and high-response, and can guarantee the system working in the max power transfer without receive the secondary information. Finally, some experiment results are presented to verify the proposed method with a 25 KW, air gap length 12 mm prototypes.