Wireless inductive-coupled power transfer and opportunity battery charging are very appealing techniques in drone applications. Weight and size are very critical constraints in drones, so the battery and the on-board electronics must be as light and small as possible. The on-board components involved in the resonant inductive-coupled wireless power transfer usually consist of the secondary coil, the compensation capacitor, the bridge rectifier, the LC-filter and the battery. This paper suggests a sizing of the LC-filter capacitor that improves the charging power of the battery. In addition, further on-board space and size is saved by using the stray inductance of the battery as filtering inductor. LTSpice simulations and experimental tests carried out on the prototype of a wireless power transfer circuit shows the dependency of the power delivered to the battery on the filter capacitor size. Finally, it is found that the power transfer to the battery is maximized by choosing the capacitor value that sets the LC-filter resonant frequency close to the double of the excitation frequency of the wireless charging. The drawback is a large current and voltage ripple in the battery.

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.

The large increment expected in the diffusion of light-electric-vehicles will raise several issues that must be addressed to cope with this trend, including battery diagnostic and maintenance services. The battery system is the most expensive part in the majority of the e-mobility devices. Therefore, battery manufacturers tend to reduce the battery cost by using simple battery management systems that provide only basic safety features. Possible advanced functionalities are not implemented and the battery may lose performanceduring its use. Widely spread maintenance centers are thus required to support the mobility electrification process, but their diffusion is limited by the high cost ofprofessional battery characterization instruments. This work proposes an open-hardware low-cost battery maintenance tool architecture that can be used with common laboratory instruments. The tool is based on a relay-matrix and a battery monitor integrated circuit. It is able to completely characterize and optimize the state of a battery independently of the battery management system and also gives a figure of the individual aging of the battery cells. The work shows the architecture and the experimental validation of a 16-cells battery maintenance tool prototype. The results demonstrate that utilizing the tool brings the battery in the best possible state and identifies the degradation of the cells in terms of capacity and resistance.

No abstract

Wireless inductive-coupled power transfer is a very appealing technique for the battery recharge of autonomous devices like surveillance drones. The charger design mainly focuses on lightness and fast-charging to improve the drone mission times and reduce the no-flight gaps. The charger secondary circuit mounted on the drone generally consists of a full-bridge rectifier and a second-order filter. The filter cut-off frequency is usually chosen to make the rectifier output voltage constant and so that the battery is charged with continuous quantities. Previous works showed that an increase in power transfer is achieved, if compared to the traditional case, when the second-order filter resonant frequency is close to the double of the wireless charger excitation and the filter works in resonance. This work demonstrates that the condition of resonance is necessary but not sufficient to achieve the power increment. The bridge rectifier diodes must work in discontinuous-mode to improve the power transfer. The paper also investigates the dependence of the power transfer increase on the wireless excitation frequency. It is found the minimum frequency value below which the power transfer gain is not possible. This frequency transition point is calculated, and it is shown that the gain in power transfer is obtained for any battery when its equivalent circuit parameters are known. LTSpice simulations demonstrate that the transferred power can be incremented of around 30%, if compared to the case in which the rectifier works in continuous mode. This achievement is obtained by following the design recommendations proposed at the end of the paper, which trade off the gain in power transfer and the amplitude of the oscillating components of the wireless charger output.