Fast Optimal Frequency Tracking for S-S Compensation WPT Battery Charger

To achieve load-independent-current (LIC) output and optimal power efficiency of a series-series (S-S) compensation wireless power transfer (WPT) battery charger, the operating frequency is normally designed to be equal or very close to the system resonant frequency. Moreover, the WPT converters would be detuned when misalignments or variations of gap distances happens in the magnetic coupler, and the constant current (CC) output and zero voltage switching (ZVS) would be further deteriorated because fixed operating frequency is adopted. This letter proposes a hill-climbing search method to track the system resonant frequency of an S-S compensation WPT battery charger, which can determine the system resonant frequency fast. Experiment results validate the effective-ness of the proposed design scheme. It is shown that system resonant frequency can be obtained with less than 0.5% error under significant variations of gap distances and misalignments of the magnetic coupler. A detailed technical analysis is presented, which provides guidance for engineering design application.