Analysis and Guidelines for Inductive Power Transfer Links Design

Abstract

Wireless energy transfer systems are becoming a revolutionary and fundamental tool for the development of the modern world. This term refers to any system without wires capable of sending energy over a certain distance through acoustic waves, mechanical vibrations, laser, electromagnetic conversion, etc. This thesis is based on the last one, specifically on electromagnetic induction systems. More than 100 years ago, Nikola Tesla left his demonstration to the world of the possibility of making such systems. Back in the 1960s, his technology began to be used for medical devices. Since then, these transfer systems utilizing magnetic induction have been increasing their complexity and usefulness over the years. It is due to its most significant benefits such as: • The reduction of batteries and increase of their useful life, such as in the inductive charging of electric vehicles. It is not only spoken of a technological key point as they are the batteries, but also of the possibility of making that the consumer charges his vehicle without the necessity to lower the same one. It is possibly the comfort of the strong points of these systems that makes it in height in investigations, as much in the universities, as in the industries. Not only in applications such as electric vehicles where the power is around 3-20kW but also in applications such as wearables and personal electronic devices that are around tens of watts. • The elimination of wires connecting the power source to the load: we are talking about medical implants: from hearing enhancement devices, pacemakers, to devices that keep the heart beating, such as Left Ventricular Assist Devices (LVADs). • The possibility of automating and modernizing systems without human supervision and intervention, as, for example, in the robotization of industry, allowing the loading of autonomous vehicles for transporting goods in warehouses at wireless stations, the clear example being Amazon. They make these systems attractive both to industry and its marketing and to universities and their research. Although these systems are not new, where for example we can find these systems in their most basic mode as in induction cookers where the powers are relatively low, and their complexity equally does not mean a tremendous technological challenge today due to its long history in the industry (Fagor as a clear example in Spain), its study, both in high power ranges as in low, has occupied a large part of congresses and magazines during the last years where it has come to more. The increase of patents on these systems is evident, reaching between 2018 and 2019 to add more than 20 thousand. However, there is an evident absence in the state of the art of design methodologies for the coils that play the fundamental role of transferring energy through a non-magnetic medium. Also noteworthy is the scarcity in the current literature of a comprehensive study of the behavior of inductive links depending on the configuration used to perform the resonance. Therefore, we can say that the apparent absence of design methodologies makes the realization of a wireless energy transfer system not trivial. Although this is not all if we think about how an inductive link is formed: a primary coil, emitter, and at some distance a secondary coil, receiver, we can understand that it is a transformer where the air gap it presents is huge, comparable even sometimes with the size of the same coil. It means that the fundamental equations we have so far are not useful. That is to say, trying to carry out an analysis of an inductive link using, for example, the Schwarz-Christofel equation to model the air gap, will make the results obtained very far from the final result, making it practically impossible to obtain the proper couplings and inductances, very necessary for the design of these systems. Therefore, finite element simulation for the design of these systems is becoming one of the fundamental tools. However, this doe