Optimal Tuning of Inductive Wireless Power Links: Limits of Performance

• Published in: IEEE transactions on circuits and systems. I, Regular papers Vol. 62; no. 3; pp. 725 - 732
• Main Authors: Halpern, Mark E., Ng, David C.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2015; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Capacitors; Circuits; Coils; Compensation; Couplings; Impedance; Impedance matching; inductive power transmission; Links; Mathematical models; Maximum power; Optimization; Tuning; Wireless communication
• ISSN: 1549-8328; 1558-0806
• DOI: 10.1109/TCSI.2014.2386771

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.