13.56MHz Wireless Power Transfer System Design And Implementation

This thesis discusses an original analysis and design methodology for a13.56MHz wirelesspower transfer (WPT) system. Particularly, it is the frst time to apply an S-matrix methodin the analysis of coupling system for wireless power transfer. Using the S-matrix method, theexistence of an optimum load impedance is approved, which enables the highest power transferefciency for the WPT system. The design of rectifer circuit is also discussed in terms of itsspecifc application in13.56MHz wireless power transfer. Then, a novel cascaded Boost-BuckDC/DC converter and its control method are proposed for the optimized load matching ofthe WPT system. Finally, all the above theoretical analysis is validated by simulation andexperimental results.The thesis is organized as follows. The history and mainstream technologies of wirelesspower transfer are frst reviewed including laser, microwave, inductive coupling and magneticresonance coupling. Especially the magnetic resonance coupling is introduced in detail, whichworks at kHz to MHz frequencies and is being widely considered as the most promising tech-nology for mid-range wireless power transfer. Then, the S-matrix-based circuit model for thecoupling system is discussed. A WPT system generally consists of fve subsystems, power am-plifer (DC/AC), coupling system (AC/AC), rectifer (AC/DC), DC/DC converter (DC/DC)and load. In order to reduce power reflection for maximum energy transfer efciency, it isknown that the input impedance of the coupling system should equal to the conjugate of thesource equivalent input impedance. The S-matrix-based analysis approves the existence of anoptimum load impedance that ensures a conjugate matching between the power amplifer andthe coupling system; therefore the power reflection is minimized. Considering the confgurationof the WPT system, an optimum load for the rectifer is then given through simulation-basedanalysis in order to match the impedance of the coupling system. A novel cascaded Boost-BuckDC/DC converter is proposed as a load matching circuit between the rectifer and the real loadfor energy transfer efciency improvement. This special DC/DC converter is controlled to workin two modes, fxed load mode for constant resistive loads, and variable load mode for variableresistor and capacitive loads such as batteries and supercapacitors. Finally, the implementa-tion of the WPT system and experimental results are mentioned. All the experimental resultssuccessfully validate the theoretical analysis and discussion.