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The switching frequency of inductive power transfer may change along with the air gap between two coils due to mutual inductance variation. The mutual inductance is conventionally estimated through experimental measurement or finite element analysis. To simplify this process, a frequency-gap model for series–series compensated inductive power transfer is proposed to calculate the unity-gain frequency based on known air gap and coil geometric parameters. Neumann's formula is applied to compute the mutual inductance of the primary and secondary coils. The experimental results show that the unity-gain frequency can be predicted with varying loads and air gaps (75–250 mm), and a demonstrated unity-gain error of <6%.
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Simple approach to calculate unity-gain frequency of series–series compensated inductive power transfer