Design of high frequency inductive power transfer systems for integration into applications

Abstract

High frequency inductive power transfer (HF-IPT) is a technology with the potential of enabling wireless power to existing and emerging battery powered devices across multiple domains, such as consumer electronics, health-care, electric transport, security and defence. For over a decade, research groups around the world have managed to demonstrate HF-IPT as a proof of concept; however, the lack of presence of the technology in medium or high power commercial products highlights the difficulty of integrating it into real world scenarios. This thesis is concerned, primarily, with the interaction and trade-offs between the power conversion stages of HF-IPT systems, ranging from the mains to the battery. The system model is structured so that crucial features for commercial exploitation, such as tolerance to misalignment and tolerance to load variation, are considered at each individual stage. Firstly, existing and novel candidate high-frequency power converters are proposed and prototyped to deal with challenges that emerge depending in the application at hand. With these prototype converter blocks, experimental work at the system level includes achieving 88% DC-DC efficiency at 6.78MHz and an air-gap of one coil radius. This, to the author's knowledge is the highest end-to-end effciency achieved in HF-IPT under similar circumstances. Experiments also demonstrate a system architecture, introduced herein, where Class E and Class EF inverters are fed directly from the mains to eliminate one power conversion stage at the transmit side when the mains interface is taken into account. A technique for HF-IPT design is then introduced with the formulation of a probability-based model which include motion and spatial freedom as design variables, allowing not only for the system to be designed and assessed for variable coupling, but also to consider the motion profile of the device being charged in the system optimisation. Two HF-IPT systems powering an application are then demonstrated. The first consists of wireless power to a drone without a battery while it hovers over a charging-pad, and the second, wireless charging of an electric scooter. These demonstrations were made possible by implementing the main contributions of this work.