DEVELOPMENT OF A HIGH QUALITY RESONANT COIL FOR LOW FREQUENCY WIRELESS POWER TRANSFER Kevin Van Acker Supervisor: Prof. dr. ir. Guillaume Crevecoeur Counsellor: Ir. Matthias Vandeputte Master's dissertation submitted in order to obtain the academic degree of Master of Science in de industriële wetenschappen: elektromechanica Department of Electrical Energy, Metals, Mechanical Constructions & Systems Chair: Prof. dr. ir. Luc Dupré Faculty of Engineering and Architecture Academic year 2017-2018 DEVELOPMENT OF A HIGH QUALITY RESONANT COIL FOR LOW FREQUENCY WIRELESS POWER TRANSFER Kevin Van Acker Supervisor: Prof. dr. ir. Guillaume Crevecoeur Counsellor: Ir. Matthias Vandeputte Master's dissertation submitted in order to obtain the academic degree of Master of Science in de industriële wetenschappen: elektromechanica Department of Electrical Energy, Metals, Mechanical Constructions & Systems Chair: Prof. dr. ir. Luc Dupré Faculty of Engineering and Architecture Academic year 2017-2018 Preface Before you lies the dissertation “Development of a High Quality Resonant Coil for Low Frequency Wireless Power Transfer”, the basis of this dissertation is to find a way to easily develop an optimal resonant coil for low frequency wireless power transfer by only having some boundary conditions for the dimensions of this coil. The dissertation has been written to obtain the academic degree of Master of Science in de industriële wetenschappen: elektromechanica at the faculty of Engineering and Architecture at Ghent university. I was engaged in researching and writing this dissertation from January to June 2018. The title and goal of this dissertation was formulated by my supervisor, Prof. dr. ir. Guillaume Crevecoeur, and my counsellor, ir. Matthias Vandeputte. Throughout the researching period the goal of this dissertation was refined by my counsellor and myself. The research I’ve done was challenging and seemingly never-ending, but I kept being interested in the subject and the diversity of the things (like coding, math, designing, manufacturing, etc …) that I have done for this research really did help with that. First, I would like to thank my counsellor ir. Matthias Vandeputte for his great counselling. He always came up with great ideas to research. When I had a problem he always made time to help me solve them, he basically taught me a new programming language (Matlab) from scratch in a few weeks. The list goes on but I have to keep this short so I will just say that I am very grateful to have had a counsellor like ir. Vandeputte. Secondly, I have to also thank my supervisor Prof. dr. ir. Guillaume Crevecoeur. He followed up my master’s dissertation very well, made time for my rehearsal presentations in his busy schedule and gave valuable feedback. I would also thank my loving girlfriend to provide mental support throughout this sometimes stressful period and listening to my complaints and moans. My friends and family I would also like to thank for supporting me. My parents deserve a special thanks for making my studies possible and also to be so understanding of my absence these months, it was sometimes hard to accept that evenings and weekends were used to do work for this dissertation and school, especially because I was the first in my near family to pursue a university/college degree, but through all this time they still kept supporting me. I hope you enjoy your reading Kevin Van Acker "De auteur geeft de toelating deze masterproef voor consultatie beschikbaar te stellen en delen van de masterproef te kopiëren voor persoonlijk gebruik. Elk ander gebruik valt onder de bepalingen van het auteursrecht, in het bijzonder met betrekking tot de verplichting de bron uitdrukkelijk te vermelden bij het aanhalen van resultaten uit deze masterproef." "The author gives permission to make this master dissertation available for consultation and to copy parts of this master dissertation for personal use. In the case of any other use, the copyright terms have to be respected, in particular with regard to the obligation to state expressly the source when quoting results from this master dissertation." Ghent, 24 June 2018 i Abstract In order to obtain the academic degree of Master of Science in de industriële wetenschappen: elektromechanica, this master's dissertation was submitted to the department of Electrical Energy, Metals, Mechanical Constructions & Systems in the academic year 2017-2018. The chair of this department is Prof. dr. ir. Luc Dupré. In this master’s dissertation a way to develop a high quality resonant coil for wireless power transfer is created. The principles of the strongly coupled magnetic resonance will be explained and investigated. Analytical and empirical formulas were used from literature to obtain characteristics of resonators that would be used by giving only the dimensions of the resonators. This was then all combined in a model that could predict the power transfer efficiency. Some optimization studies were conducted to investigate the optimal dimensions for power transfer with strongly coupled resonators. A way to find the optimal load resistance was found by using an optimization function with the model. An easy way to optimize the dimensions of the resonators was also found by using a Matlab code. The optimal position for a five-resonator power transfer system was also investigated and found, the optimal position for the resonators is not uniformly spacing these resonators over the desired transfer distance but rather have the second resonator be closer to the first resonator where the source is connected to and the second last resonator closer to the last resonator. ii Extended abstract EN Development of a High Quality Resonant Coil for Low Frequency Wireless Power Transfer Kevin Van Acker Supervisor: Prof. dr. ir. Guillaume Crevecoeur Counsellor: Ir. Matthias Vandeputte Abstract: In this dissertation wireless power The currents that flow in these resonators will be transfer via strongly coupled resonant coils will investigated and modelled. After that a model that be investigated. The basics of how energy is can predict these currents will be made with formulas transferred will be shown. The main focus is to found in literature. The formulas will be validated with create a method to develop a high quality some measurements. When the individual formulas resonant coil. This will be done by creating a seem to be correct for these measurements, predicting model in Matlab that will predict the measurements to validate the whole model can then power transfer efficiency of a certain resonator be performed. system in resonance. II. PRINCIPLES OF SCMR I. INTRODUCTION Using the strongly coupled magnetic resonance In recent years wireless power transfer has wireless power transfer method, power is transferred gained in popularity for consumer devices, e.g. by using a magnetic field. The magnetic field is charging smartphones and other devices wirelessly. created by the current that runs through the coil of There are a few ways to transfer energy wirelessly. the first resonator, as stated by Ampères law. An The method that will be discussed here is strongly alternating magnetic field is induced by the coupled magnetic resonance. This method has a alternating current that runs through the first coil. A lower power transfer efficiency than other methods second resonator is placed near the first resonator for short (a few centimetres) and long distances (a so that the coils of the resonators are magnetically few dozens of metres to kilometres) but seems to be coupled with each other. The coil of the second the best solution for mid-range applications (range of resonator is now in a changing magnetic field a few centimetres to a couple of metres). because of the alternating current in the first Applications for strongly coupled magnetic resonator. Because of Faraday’s law, the changing resonance can be electric vehicles, robots and other magnetic flux of the magnetic field will generate a electronic devices that needs to be charged at a changing electric field in the coils in the form of an distance for optimal convenience. electromotive force. This electromotive force is then Strongly coupled magnetic resonance (SCMR) the source in the second resonator that will drive will be investigated in this dissertation. This method current through the components of the second of wireless power transfer uses at least two resonator. resonators. Resonators are electric circuits that consists out of a coil and a capacitor. To transfer power with these resonators a high frequency voltage source needs to be connected to one resonator (primary resonator). A load then needs to Figure 1: Circuit of a two resonator power transfer system. be connected to the other resonator (secondary resonator). In Figure 1 a representation of the two resonators can be seen. When the power of the source is iii derived by using circuit theory the following The expression for the efficiency that was previously expression for the input power of the system can be shown was for a two-resonator system that was stated (Huang, Zhang, & Zhang, 2014): directly fed by a voltage source. There is also 2 2 2 2 {푅1[(푅2 + 푅퐿) − 푋1 ] + (휔푀12) (푅2 + 푅퐿)}푉푠 another method that is used to achieve SCMR, this 푃푖푛 = 2 2 2 [푅1(푅2 + 푅퐿) − 푋1푋2 + (휔푀12) ] + [푅1푋2 + (푅2 + 푅퐿)푋1] method is with a dedicated driver and load coil. These driver and load coil are meant to be connected The same can be done to derive the output power of to the source (driver coil) and to the load resistor the system (the power that the load resistor 푅퐿 gets): (load coil). An illustration can be seen in Figure 3. 2 2 (휔푀12) 푉푠 푅퐿 푃표푢푡 = 2 2 2 [푅1(푅2 + 푅퐿) − 푋1푋2 + (휔푀12) ] + [푅1푋2 + (푅2 + 푅퐿)푋1] The efficiency 휂 of the power transfer of the circuit in Figure 1, where the angular frequency is 휔, then becomes: Figure 3: Schematic of the setup of the coils for SCMR 2 power transfer with a dedicated driver coil and load coil.