DC-link capacitor sizing method for a wireless power transfer circuit to be used in drone opportunity charging

Resonant-coupled inductive Wireless Power Transfer systems are very appealing as opportunity charging systems for drone applications. Drones are compact systems in which weight and size are critical constraints, so the on-board electronics and the battery must be as small and light as possible. The paper presents the LTSpice simulation analysis of a circuit on the WPT secondary side that uses the intrinsic inductance of the Li-poly battery and only an external capacitor as filter of the full-wave bridge rectifier that typically constitutes the DC-link. The analysis shows the trade-off between the power delivered to the battery and the capacitor size. It results that it can be found a capacitor value that maximizes the power transfer to the battery at the expense of a non-optimal transfer efficiency and increased ripple in the battery current. That value sets the LC-filter resonant frequency close to the double of the excitation frequency of the WPT system.