Research On Magnetically Coupled Resonant Wireless Power Transfer With Coil Arrays

The magnetically coupled resonant(MCR)wireless power transfer(WPT)technique was proposed in 2007.It employed two high-quality resonant coils to realize coupled resonance in order to transfer electrical energy through electromagnetic near fields which are mostly of magnetic.In comparison with the inductive wireless power transfer,it has higher power transfer distance and efficiency;in comparison with the radiative wireless power transfer,it has very small undesired external radiation.The MCR technology has attracted great attention and has found potential applications such as wireless charging of electric vehicles,wireless power supply for smart homes,noninvasive charging of implanted medical devices,wireless charging of wearable devices and wireless power supply to wireless sensor networks.Technical progresses have been made for the MCR-WPT technology in the areas such as enhancement of power transfer efficiency(PTE)in the over-coupled and under-coupled regions,minimization of the effects of lateral coil misalignment(i.e.,nonuniform PTE distribution)and angular misalignment(i.e.,rotation of the receiver).However,the progresses are limited,and new advances or breakthroughs are still much desired in order to make the MCR-WPT systems feasible under various practical conditions with high power transfer efficiencies.Along this line,this thesis derives the equations of PTE for the planar 3-and 4-coil MCR-WPT systems,investigates the effects of the number of turns in a coil,the gap between the turns and the width of the coil on the quality factor,and presents the procedure for optimizing coil arrays that are used as a unit cell of the new transmitting antenna arrays proposed in this thesis.The thesis applies the equivalent circuit model and electromagnetic field theory to analyze the operational principles of the MCR-WPT systems,and then develops and optimizes the planar spiral array coils,three-dimensional array coils,and a shape-reconfigurable modularized MCR-WPT system.The thesis makes the following specific contributions.First,the thesis introduces the basic structure of the conventional multi-coil MCR-WPT array system,applies the coupled theory to develop the WPT mechanism of the coil array system,and employs the circuit theory to compare the 2-coil and 4-coil WPT systems.Then this thesis derives the equations of PTE for the 3-coil and 4-coil MCR-WPT systems and analyzes the relationship between geometries of the coils and quality factor.Based on the analysis,the thesis proposes the procedure that optimizes the planar coil array to be used as a unit of the new transmitting array systems presented in the thesis.Secondly,the thesis proposes the ‘8’-shape planar spiral coil-array system and 3×3 multi-layer spiral coil-array structure of the MCR-WPT system.The proposed systems increase the power receiving area,generate a uniform power-transfer-efficiency distribution zone,and improve the receiver’s mobility under lateral misalignment.By conducting theoretical analysis,electromagnetic simulations and experimental tests of the ‘8’-shape planar spiral array coils of MCR-WPT system,the proposed systems are shown to improve the uniformity of power transfer distribution and achieve the position mobility and flexibility of the power receiver,in comparisons with the conventional coil array system.With the proposed coil array systems,a wireless charging table is built and it effectively delivers power wirelessly to LED lamps,Bluetooth speakers and smartphones.Thirdly,the thesis develops two three-dimensional MCR coil-array WPT systems,the L-shape and the magnetic tank systems.The L-shape array system improves PTE in over-coupled and under-coupled regions with the addition of a vertical transmitting resonant coil between the transmitter and receiver.The equivalent circuit model and optimization method are developed for the L-shape array system;numerical simulations with HFSS and Agilent ADS and experiments are carried out to verify the proposed systems.The magnetic-tank coil array system addresses the issue of the drop of the PTE due to lateral misalignments between the WPT transmitter and receiver.The magnetic-tank system is analyzed and experimentally tested;they both verify that the magnetic tank system can improve PTE over angular misalignments.Thus,both the L-shape and magnetic-tank systems are shown to be capable of providing effective wireless power transmission.Fourthly,the thesis proposes a shape reconfigurable modularized MCR-WPT system for multi-purpose wireless power supply or charging applications.It allows flexible combinations of transmitting and receiving modules to cater to different application needs.Again,the operational principle of the reconfigurable system under different application scenarios is theoretically analyzed;numerical simulations and experimental tests are conducted.Both the simulation and experimental results verify that the proposed configurable system not only provides the position-flexibility or mobility of the receiver but also can change its shape to be conformal with the devices to be charged or powered wirelessly.Finally,the thesis presents the possible future research and development directions of wireless power transfer and their rational.