Design and Analysis of a Load-Independent Three-Coil Inductive Power Transfer System for Battery Charging

This paper presents a novel three-coil inductive power transfer (IPT) system for enhanced battery charging applications. While conventional two-coil systems have been widely studied, the addition of an intermediate coil introduces unique advantages that remain largely unexplored. Herein, we propose and analyze two compensation topologies LCC-S-S compensation topology and S-S-S compensation topology to achieve inherent constant current constant voltage (CC/CV) charging characteristics without requiring complex control strategies. Through comprehensive mathematical modeling and analysis, the fundamental relationships between system parameters and output characteristics have been derived to enable systematic design optimization. Moreover, a detailed parameter design methodology is presented that ensures the desired CC/CV profile while maintaining high efficiency. Finally, the theoretical analysis is validated through an experimental prototype, demonstrating good load-independent behavior with a peak DC-DC efficiency of 94.9%, Even under misalignment, the efficiency can still maintain above 90%.