Design Considerations for Multimegahertz Resonant Inductive Power Transfer

MHz-frequency inductive wireless power transfer holds the promise of compact and cost-effective wireless power transfer. However, due to the sensitivity of the high-frequency circuit operations to the parasitic components, these systems are universally less efficient, on a dc-dc basis, than wireless power systems operating at conventional lower frequency regimes. This article presents the design considerations for inductive power transfer systems operating at multi-MHz frequencies. Specifically, this work comprehensively analyzes the tradeoffs of selecting different compensation topologies, including series-series, series-parallel, parallel-series, and parallel-parallel compensations. The article also provides guidelines for incorporating parasitic components of semiconductor devices into a multi-MHz circuit design to improve transmission efficiency. Validating the design methodologies, we built three 300-W inductive power transfer systems using series-series, series-parallel, and parallel-parallel compensations, all achieving an ac-ac efficiency above 96%, and compared their performances in detail. Finally, we demonstrate a 6.78-MHz prototype inductive power transfer system that delivers 1.7-kW power with a dc-dc efficiency of 95.7%.