Research On Inductively Coupled Wireless Power Transfer System With Asymmetrical Compensation

Wireless power transfer(WPT) is worth researching for it could reduce power loss by replacing traditional cable power transfer. Inductively Coupled Power Transfer(ICPT), adopting electromagnetic induction to transfer power wirelessly, is considered as one of the most practical WPT technologies currently.The most basic part in ICPT is loosely coupled transformer, who converts electric power into magnetic power and therefore achieves wireless power transfer via magnetic field. However, there are certain problems in loosely coupled transformer, such as limited transfer distance, poor coupling between two sides, and large leakage inductance, which result in low transfer efficiency of ICPT. As a solution to these problems, compensation circuits based on circuit resonance are usually applied in ICPT.Classic compensation structures such as S-S compensation and double-side LCC compensation are symmetrical designed in both sides. These compensation structures certainly and notably increase transfer efficiency, while some disadvantages existing in them. S-S compensation highly relys on the loosely coupled transformer for its total voltage gain is determined by turns ratio, which greatly limits the design of loosely coupled transformer. Double-side LCC compensation has the problems of non-constant output, difficulty on achieving soft-switching, and excessive amount of circuit components. To overcome these disadvantages, this thesis will propose a novel series of asymmetrical compensation structures based on analysis and modeling on classic compensation structures. Proposed compensation structures will achieve zero-voltage switching and open-loop constant voltage output with an adjustable voltage transfer ratio unrestricted of turns ratio.The thesis will provide research on design of loosely coupled transformer as well. Theories on loosely coupled transformer design currently are either qualitative or inexact. Theories on regular transformer design, however, are not applicable in loosely coupled transformer design. Quantitive design theory for loosely coupled transformers based on regular transformer model and magnetic resistance analysis will be propoesd. Besides, design processes of two sorts of widely adopted loosely coupled transformers will be provided based on proposed theory, and verified by FEA simulation.A prototype aiming to verifying the theories will be established based on proposed compensation structures and loosely coupled transformer design. Simulation results based on Pspice will be given, as well as experimental results based on the established prototype. The prototype will achieve 230 W power transfer at a total efficiency of 86%, in a wireless transfer distance of 5.0 cm, and with a space limitation of 30 cm×30 cm×5 cm.