Large magnetic field volumes associated with coreless high frequency inductive power transfer (HF-IPT) systems allow multiple receivers to be powered from one transmitter, but also provide greater probability for foreign objects to couple to the system. Knowledge of the types of objects (legitimate receivers or otherwise) that are coupled to the transmitter is critical. Such knowledge on the transmit side would allow the system to be deactivated in the presence of foreign objects, and to determine the exact state of tuning of the receivers so that it may adjust itself accordingly to optimise system performance. This paper introduces a technique to calculate the induced voltage generated by coupled receivers and foreign objects on the transmit coil in real-time. Changes in the position or electrical quantities of the receivers, and foreign objects, alter the induced voltage on the transmit coil, and with it the trajectory of the switching waveforms of the inverter driving the transmit coil. From the shape of these waveforms, information on the phase and amplitude of the induced voltage can be extracted, thus enabling the induced voltage on the primary to be estimated with a single, easy to access, voltage measurement, which is easier than estimating the induced voltage from measurements of coil current and total coil voltage. We used a support-vector-machine (SVM) to perform regression analysis on the drain voltage data. The experimental setup uses a 100 W, 13.56 MHz Class EF inverter, and the model was generated from a large number of samples of the drain voltage waveforms operating at different known loads. These were generated from our in-house HF-IPT test load, which uses a Class EF synchronous rectifier. The results allow the induced voltage on the transmit coil to be estimated in real time from the drain voltage waveform alone, with a normalised root mean square error of 1.1 % for the real part (reflected resistance) and 1.2 % for the imaginary part (reflected reactance).This paper is accompanied by a video file demonstrating the experiments.

This paper presents foreign object detection (FOD) methods for MHz wireless power transfer (WPT) systems. Unlike current FOD implementations, the presented methods can operate without requiring a feedback loop from the wireless power receiver to the transmitter. This allows complete decoupling of the transmitter and receiver and therefore reduces the design complexity and cost of the system. The developed FOD methods were implemented on a 13.56 MHz WPT and experimental results are presented showing successful detection of a wide range of objects regardless of the loading condition of the system.

This paper presents the development and characterisation of an inductive link to assess and compare inductive power transfer (IPT) systems that operate at 6.78 or 13.56 MHz. First, the properties of two equal air-core coils were obtained from simulations and corroborated experimentally. Then, the coupling factor between the coils was calculated in function of separation and misalignment. A receiving-end circuit, comprised of a capacitance and a resistive load, was also characterised in order to reflect different loads to the transmitter at different tunings and couplings, and therefore represent the effects produced by changes in coupling and variations in the rectifier's input impedance. The link was tested, firstly using a Class E inverter and then a load-independent Class EF inverter, both at power levels lower than 200 W. The reflected load was changed by altering coupling, and the tuning capacitance. A comparison between these inverter topologies handling highly reactive loads is shown here for the first time.

This paper reports on the design and development of a wireless charging solution for a DJI Matrice 100 quadcopter drone. The system is based on a high frequency inductive power transfer system built with lightweight copper pipe air-core coils at both ends and lightweight electronics at the receive side. The developed system is capable of delivering power to the drone at the same rate as the original wired charger (100 W) when landed at any position on the charging pad, regardless of the lateral misalignment or angular orientation. The charging pad is circular with a one-metre diameter, therefore allowing for a lateral misalignment of up to 25 cm. The system has an average mains-to-battery efficiency of 70 % and enables the drone missions to be completely autonomous as it eliminates the need for human interference for battery recharging or swapping.

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