A Novel S–S–LCLCC Compensation for Three-Coil WPT to Improve Misalignment and Energy Efficiency Stiffness of Wireless Charging System

Recent studies have proven that a three-coil wireless power transfer (WPT) design shows better performance and has higher efficiency compared to the two-coil designs, especially when the source resistance and transmission distance between the primary and receiver coil increases. The three-coil WPT system, similar to a two-coil system, is capable of achieving constant output current (CC) and constant output voltage (CV) with ZPA. However, in the CV mode of the conventional three-coil design, the efficiency of the light-load system dramatically decreases as the load becomes smaller. In this article, a new series-series-LCLCC (S-S-LCLCC) compensation design for the three-coil WPT system with load-independent output voltage, which is capable of realizing ZPA characteristics during the entire process of the charging process, is proposed. The new design is capable of significantly improving the energy efficiency stiffness against the load variation, misalignment, increasing the flexibility to optimize the system efficiency, reducing the voltage stress, and increasing the power delivery to load compared to the conventional topology. The experimental design shows that the overall trend of efficiency of the proposed design is higher than the conventional design as the load decreases and the new system has approximately 10% higher efficiency when the battery equivalent load resistance reaches 222 Ω.