Use of primary-side information to perform online estimation of the secondary-side information and mutual inductance in wireless inductive link

It is well-known that the power transfer efficiency of wireless inductive link depends on factors including the mutual inductance between the primary and secondary coils, quality factors of the coils, and resonant tank components. It is thus advantageous to have the real-time information about the aforesaid factors, in order to determine the optimal operating frequency and monitor the load condition. This paper will present a technique that utilizes the primary-side electrical quantities to perform real-time estimation of the mutual inductance, value of the secondary-side resonant capacitor, and electrical quantities on the secondary side. The technique can be applied to three scenarios: 1) with unknown value of the secondary-side resonant capacitor and known secondary-side voltage, 2) with known value of the secondary-side resonant capacitor and unknown secondary-side voltage, and 3) unknown value of the secondary-side resonant capacitor and unknown secondary-side voltage. Detailed mathematical treatment will be given. An experimental prototype using planar transformer has been built and evaluated on a test bed. This technique is also implemented as a control scheme of a cascaded converter to regulate the output power. Experimental results are found to be in close agreement with the theoretical predictions.