With the developments of mobile and implantable devices, wireless power transfer (WPT) has become increasingly attractive to free a variety of electronic systems from power cords and batteries. Resonant inductive coupling is the leading technology of WPT, offering high efficiencies (>75%) with power levels from microwatts to hundreds of watts. This thesis focuses on a resonant four-coil inductive WPT technology. It develops numerical models of the four-coil WPT system (incorporated into a Matlab simulator) and validates them by experiment. It then develops numerical tools using Matlab for computing self- and mutual inductances for inductors of arbitrary shape and orientations using the method of magnetic vector potential and validates these tools by experiment. Inductance-calculation tools are designed to be user-friendly and are intended to be employed as a substitute for FEA (Finite Element Analysis). Effects of high magnetic permeability materials like ferrite sheets on the self- and mutual inductance of coils are studied, and Matlab-based numerical tools are developed to analyze such effects. These tools were validated by experimental work. A proposed design methodology employing the method of reflected impedances in loosely-coupled inductors is applied to the design of a four-coil WPT presented in this thesis. This method reflects impedances sequentially through the inductors from the system load to the driving source and is incorporated in a spreadsheet calculator. A design derived from this method is subjected to experimental validation and efficiencies exceeding 76% are noted with various spacings between the transmitting and receiving coil pairs. The method is shown to be useful for first-pass design, but significant effects are noted due to mutual inductances neglected in the design procedure. The full model is necessary for accurate simulation results. Conclusions and suggestions for future work are presented.
Date of publication
Annam, Sravan, "Four-Coil Wireless Power Transfer Using Resonant Inductive Coupling" (2012). Electrical Engineering Theses. Paper 19.