Analysis Of Transfer Power And Efficiency And Optimization Design For Wireless Power Transfer Via Magnetic Resonance Coupling

Due to the advantages of long transfer distance and high transfer efficiency,wireless power transfer via magnetic resonance coupling?WPT/MRC?has broad application prospects in people's daily life.The basic technical principle and characteristics of WPT/MRC have been explored deeply after years of scientific research,but the practical problems limit the application and popularize of this technology.Nowadays,to explore the transfer characteristics of special WPT system and promote its practicability have become the hotspots in WPT field.Focus on electric vehicle?EV?dynamic wireless charging system,planar wireless charging platform,high-frequency low-power system,and mid-range WPT system,this thesis analyzes the characteristics of each system and put forward the optimization methods of improving transfer efficiency,transfer distance and promoting the stability.The researches provide feasible technical solutions to promote the practicability of WPT/MRC.The main works and innovative points of this thesis are listed as follows.?1?To solve the transfer power fluctuation caused by position variation of transfer coils in electric vehicle dynamic wireless charging system,the primary non-resonant and secondary resonant series-series?SS?WPT system is proposed.The reactance of primary side is optimized to maintain output power.And average efficiency is improved by the appropriate DC-DC module in secondary side.The series-series WPT system with boost converter in secondary side is setup to measure the transfer features in the condition of coil misalignment.The experimental results show while the change rate of coil coupling coefficient is 200%,the measured transfer power is maintained stable and the average efficiency is up to 88.6%.?2?The close relationship between relative charging height and magnetic field distribution in the charging plane above the square transmitter is explored to show that the ordinary square coil has the limitation in regulating uniform magnetic field when the charging height is overlarge.A new multiple-antiparallel square transmitter is present to produce uniform magnetic field in relatively long-distance charging plane to weaken the fluctuation of load power while the location of receiver changes.A 5 cm-height WPT system adopting ordinary square transmitter and proposed transmitter is setup to verify theoretical prediction.The measured output power and efficiency are kept stable effectively by adopting the proposed transmitter when the receiving coil moves in the 26 cm×26 cm charging area.?3?In the high-frequency low-power WPT system,the frequency splitting of transfer power will occur in close transfer distance and the transfer power will decrease sharply with the increasing distance.To improve the stability of transfer power,a new mixed-resonant WPT model based on non-identical coils is proposed.A couple of non-identical coils are utilized to suppress coil coupling strength and eliminate frequency splitting in close distance.The transfer distance with high power transfer efficiency is enlarged by the optimization design of the mixed-resonant circuit.Then,a 9.7 MHz mixed-resonant WPT system using non-identical coils is constructed.The measured results show that there is no frequency splitting and decaying value of transfer coefficient|S₂₁|is just 3.4 dB when the transfer distance increases from 3 cm to 24 cm.?4?In order to increase transfer efficiency of mid-range WPT system,the transfer characteristics of four-coil WPT system are explored and the effects of frequency,coil quality factor and coil matching on transfer efficiency are summarized.Additionally,based on the electromagnetic focusing effect of negative permeability metamaterial?MA?,a resonant-ring MA is designed to enhance coil coupling.This MA slab has a negative relative permeability?=-1.1 at 2.8 MHz.Two four-coil WPT systems adopting square transfer coils and circular transfer coils are setup to study the variation rule of efficiency with the MA slab.The transfer efficiency of the WPT system adopting circular coils exceeds that of square transfer coils 5%.When the MA slab is loaded in the optimal location,the increased efficiencies in 1.4 m and 2 m transfer distances are 11.4%and 5%,respectively.The experimental results verify the significance of MA in improving the transfer efficiency in mid-range WPT system.Aim at increasing transfer efficiency,distance and enhancing the stability of transfer power,the features of four kinds of WPT systems are researched deeply.The optimization design methods are proposed and will lay the foundations for improving the stability and practicability of WPT systems.Meanwhile,combing the MA with the WPT technology has verified that MA can play an important role in enhancing energy transfer efficiency and will provide an effective technical approach for improving WPT systems.