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This paper presents the design of a multi-MHz inductive power transfer (IPT) system showcasing lightweight and energy-efficient solutions for non-radiative wireless power transfer. A proof of concept is developed by powering a drone without a battery that can hover freely in proximity to an IPT transmitter. The most challenging aspect, addressed here for the first time, is the complete system-level design to efficiently provide uninterrupted power flow while allowing for variable power demand and highly variable coupling factor. The proposed solution includes the design of lightweight air-core coils that can achieve sufficient coupling without degrading the aerodynamics of the drone, and the design of newly developed resonant power converters at both ends of the system. At the transmitting-end, a load-independent Class EF inverter, which can drive a transmitting-coil with constant current amplitude and achieves zero-voltage switching for the entire range of operation, was developed; and at the receiving-end, a hybrid Class E rectifier, which allows tuning for large changes in coupling and power demand, was used. For the demo, the range of motion of the drone was limited by a 7.5 cm nylon string tether, connected between the center of the transmitting-coil and the bottom of the drone. The design of the IPT system, including all the power conversion stages and the IPT link, is explained in detail. The results on performance and specific practical considerations required for the physical implementation are provided. An average end-to-end efficiency of 60% was achieved for a coupling range of 23%-5.8%. Relevant simulations concerning human exposure to electromagnetic fields are also included to assure that the demo is safe, according to the relevant guidelines. This paper is accompanied by a video featuring the proposed IPT system.
Arteaga et al. (Thu,) studied this question.