Optimal Tuning of Inductive Wireless Power Links: Limits of Performance

This paper shows how to choose compensation capacitors for optimal performance in two-coil fixed-frequency inductive wireless power links having a series-parallel (SP) configuration. First, for the SP circuit with given coils, coupling and sinusoidal input voltage, it is shown how to calculate nonnegative valued capacitors to maximize power delivered to a given resistive load. Exact conditions for such a compensated system to deliver the maximum power obtainable from a circuit with the same resistances and an ideal transformer with optimal turns ratio are presented. The second main contribution is a method for selecting compensation capacitors to maximize a weighted sum of efficiency and delivered power to obtain a trade-off between these two quantities. This can allow flexible performance with a given set of coils. All of this can be implemented without numerical optimization software. The results are illustrated by numerical examples and supported by experimental measurements.