Title Page OPTIMUM MODELLING OF FLUX-PIPE RESONANT COILS FOR STATIC AND DYNAMIC BIDIRECTIONAL WIRELESS POWER TRANSFER SYSTEM APPLICABLE TO ELECTRIC VEHICLES PhD Report Student: Mr. Babatunde Olukotun, MSc. (Hons) Supervisor: Prof. RWG Bucknall Co-Supervisor: Dr Julius Partridge Department of Mechanical Engineering University College London I, Babatunde Olukotun confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirmed that this has been indicated in the thesis. February 2020 1 Abstract Wireless power transfer (WPT) technology enables the transfer of electrical power from the electric grid to the electric vehicles across an airgap using electromagnetic fields with the help of wireless battery chargers. WPT technology addresses most problems associated with the “plug-in” method of charging EVs like vandalization, system power losses, and safety problems due to hanging cables and opened electrical contact in addition to the flexibility of charging electric vehicles while in a static or dynamic mode of operation. Significant research has been undertaken over the years in the development of efficient WPT topologies applicable to electric vehicles. A preliminary review of these revealed that the ferrite core WPT is a promising and efficient method of charging electric vehicles. The charging method is suitable for wireless charging of electric vehicles because of its low cost, high efficiency and high power output. This research proposed the use of the flux-pipe model as a suitable ferrite core, magnetic resonance coupled-based WPT system for the charging of the electric vehicle. The traditional flux-pipe model has some specific benefits which include high coupling coefficient, high misalignment tolerance and high efficiencies under misalignment conditions. However, it has a major drawback of low power output due to the generation of an equal amount of useful and non-useful fluxes. A set of governing equations guiding the performance output of a WPT system was presented. It was identified that the losses in the WPT system can be minimized by reducing the value of the maximum magnetic flux density while the power output and efficiency can be increased by increasing the value of the coupling factor and quality factor. Based on these findings, 3-D finite element modelling was employed for the optimal design and analysis of a typical flux-pipe model for higher coupling strength, high power output and low losses. The magnetic coupling performance of flux-pipe resonant coils was enhanced with an increased number of turns along the core length relative to increasing the width of each coil turns along the coil width. The high power transfer and efficiency was attained by splitting of the coil windings into two in order to reduce intrinsic coil resistances; copper sheet was employed as a shielding material in order to reduce the eddy current losses and finally, an air gap was introduced in the ferrite core in order to reduce the core losses and invariably increased the amount of excitation current required to drive the core into saturation. The proposed optimization methodology results in the creation of two models for application in static and dynamic charging operations respectively. From the simulation results presented, the model designed for static charging operations can transfer up to 11 kW of power across the airgap at a coil-to-coil efficiency of 99.12% while the model design for dynamic charging of electric vehicles can transfer up to 13 kW of power across the airgap at a coil-to-coil efficiency of 98.64% without exceeding the average limit specified for the exposure of human body to electromagnetic fields. 2 Impact of Research Work In this thesis, a system-level engineering and simulation-based approach is presented and employed for the engineering design of novel coils for wireless charging systems. The methodology comprises an initial validation of model designs obtained from published literature. These are then subjected to an iterative simulation process to fine-tune designs in order to achieve an optimal specification for the present application. Wherever possible, the modelled operation is compared with published practical results in order to ascertain the degree of validity of the modelling undertaken. This has enabled the optimization of proposed engineering designs. A numerical method, finite element modelling (FEM) using Ansys Maxwell 3-D software is chosen and employed for the model designs, analyses, optimization and evaluations. The initial boundary conditions were carefully selected based on the analysis of published designs. FEM as a numerical method is employed because it can easily handle very complex geometry involving an infinite degree of freedom cutting across a wide range of engineering context such as dynamics, solid mechanics, fluids, heat flows, electrostatic, and electromagnetics. For this research, FEM methodology was applied for the optimal design and analysis of ferrite core, magnetic resonance coupling-based wireless power transfer systems. The research and modelling methodology applied in the present work resulted in the creation of two ferrite-cored flux-pipe models with high power transfer capability and low losses. The optimal model designs still retain the inherent high coupling capability associated with typical flux-pipe coil designs. The two models also have potential application in the bidirectional transfer of wireless power for static and dynamic operations at very high coil-to-coil efficiencies. The model design for dynamic charging is best suited for segmented coil array systems which come with benefits of low electromagnetic exposure and a low number of compensation capacitors. With eventual creation of prototype designs and practical demonstrations, the models offer a cost-effective wireless power transfer systems with additional capability for vehicle-to-grid integration. The system-level engineering and simulation-based design approach employed in this research could be deployed for optimal model designs and optimizations in other areas of engineering. The methodology reduces the high cost involved in the production of numerous prototypes using the traditional iterative process by creating numerous virtual prototypes in the modelling and simulation stage. The majority of the iterative optimization and testing process is undertaken at the model design and simulation stage, thus, significantly reducing the number of prototypes production at the fabrication stage. 3 Acknowledgements I wish to acknowledge the supervisory roles of my main supervisor Prof. RWG Bucknall for his invaluable academic guidance, advice and support with regard to the concepts, design, development and completion of this research work. I also wish to acknowledge the contribution of Dr Partridge Julius. I must especially thank him for the invaluable hours of discussion on the research gaps and areas of optimization. I will also like to acknowledge the technical advice and editorial work of Engr. Konrad Yearwood in the course of writing this thesis. His critical review and feedbacks were helpful in ensuring that this report was of high standard and quality in terms of technical contents and thesis structure. I will also like to appreciate the experts at MDPI Journal of energies for their critical reviews and recommendations in the course of this research, which was helpful in the analysis, validation and evaluations of proposed designs. 4 Appreciation I wish to especially express my profound gratitude and sincere appreciation to the almighty GOD the Maker of heaven and earth for the power and grace to successfully complete this research. I wish to also appreciate my parent Rev and Mrs Joseph Olukotun for their financial and moral support throughout the course of my academic career and progress till date. I also wish to appreciate Nigeria former President, Dr Goodluck Ebele Jonathan for his innovation and successful implementation of the Presidential Special Scholarship for Innovation and Development (PRESSID) in which I am a beneficiary. I also wish to appreciate my scholarship guarantors: Pastor Kelvin Dariya and Mr Micah Olarewaju. I will also not forget my academic guarantors: Prof. Oyetunji and Prof. Bello. A special appreciation goes to my wife, Dorah for her advice and support. I will like to appreciate sons: Jadon and Jaymin and my siblings: Ibukun, Adekunle, Adeniyi, Oluwagbenga and Abigail for all their support towards the progress in my academic career. Finally, I will like to appreciate my colleagues at the Federal University of Technology, Akure, friends and well-wishers for their prayers, support and encouragement. 5 Contents Title Page .......................................................................................................................................................................................... 1 Abstract............................................................................................................................................................................................. 2 Impact of Research Work .......................................................................................................................................................... 3 Acknowledgements ..................................................................................................................................................................... 4 Appreciation ..................................................................................................................................................................................