Improved Efficiency of Weakly Coupled Wireless High-Power Transfer Systems by Loss-Separation Strategy

In the equivalent T-model of the loosely coupled transformers, the small mutual inductance can lead to higher conducting currents, which cause high losses in the primary circuit and significantly reduce the overall transfer efficiency under weak-coupling states. To overcome this challenge, this paper proposes a strategy to separate the primary loss components from the weak-coupling stage. In the proposed strategy, a gyrator in the form of a double-resonance T-block is added just before the weak-coupling stage to improve the overall efficiency. Then, the strategy is realized by various topologies such as compensating circuits, added coils, isolated transformers, and integrated-/split- inductors/coils. Also, the optimized designs and component selection for resonance and the mathematical derivation for optimal load resistances were investigated. ANSYS comparative analyses of the topologies are presented by considering practical aspects, including component designs, power flows, transfer efficiency, resonance frequency shifting, and optimal loads. Finally, the analyses were validated using the fabricated experimental setups and demonstrated an efficiency improvement of about 5% for a case with a coupling factor of 0.1. The proposed strategy offers suggestions for industrial designs of high-power wireless battery charging systems using resonant inductive coils.