Development of the gradient-based coil layout optimization for effectively designing wireless power transfer systems

Abstract

For the past decade, wireless power transfer (WPT) systems have been applied from low power to high power electric and electronic devices: mobile phones, mobile robots, biomedical implants, LED TVs, laptops, and electric vehicles. In order to satisfy the requirements (e.g. transferred power capacity and mass) and improve the performances (e.g. power transfer efficiency) of products, all design factors for WPT systems should be thoroughly investigated. Among them, the design of coils (i.e. the determination of their location, shape, dimension, and number) is very critical for extremizing the performance of WPT systems. In the literature, the coil design for WPT systems has been explored through conventional design approaches (e.g. Trial-and-error-based design approach, partial domain search, design of experiment, etc.) and design optimization approaches (e.g. size and shape optimization). The conventional design approaches have not been dependent on mathematical programming, but significantly dependent on the designers’ engineering intuition. Furthermore, they cannot guarantee a feasible design under multiple design constraints, and cannot consider the coupling effects among all design factors (i.e. they explore only partial design domains). As a more systematic and efficient design approach, a shape optimization framework for WPT systems was recently proposed in order to determine the optimal shapes for coils and ferrite while satisfying multiple constraints. However, there was an inherent limitation in the proposed shape optimization: the topology of the coil and ferrite was predetermined and fixed during optimization. This dissertation presents a novel systematic and efficient coil layout (or topology) optimization for WPT systems which can determine the optimal coil layout to extremize an objective function (e.g. power transfer efficiency or mass) while satisfying all requirements based on multiple structural and electrical design variables under the given conditions. The proposed method is based on five new concepts: (1) FG-based coil representation which is consisted of relative and effective coil turns

(2) Effective turns for always making closed coil loops

(3) Effective coil turns to evaluate mass in FG-based coil representation

(4) Smooth boundary (SB) coil representation in order to representation the more precise coil layout

and (5) Resonance determination in order to determine the optimal compensated capacitance. The application examples are to design the optimal coil layout of the wireless portable charger in situations where you do not know the receiver coils or the transmitter coils or both. Then, the optimized coil layouts are experimentally validated in order to demonstrate the feasibility and potential of the proposed method. Therefore, this paper contributes to minimize the time and cost of product development by presenting the direction of optimal coil layout design for wireless power transmission system under various conditions.