Research On The Transfer Characteristics Of Wireless Power Transfer Via Magnetic Coupling

Wireless power transfer via magnetic resonance coupling (WPT/MRC) hasbeen proposed in recent years as a new solution in the field of WPT. Compared withother WPT technologies, WPT/MRC is appropriated for mid-range WPT with highpower and efficiency, and hence attracts tremendous interests. However, the transferbandwidth of WPT/MRC is narrow, and the transfer distance needs to be extendedto meet the requirement of some application environments. Moreover, WPT/MRCnot only cannot transfer power at long distance but also can be affected byfrequency splitting phenomenon at close distance and the transfer efficiency decaysrapidly. Therefore, WPT/MRC suffers dramatical variation of transfer efficiency. Toimprove WPT/MRC from the above aspects, this thesis focuses on the transfercharacteristics of WPT/MRC based on the analysis of the mutual inductance.First, an analytical method for the magnetic coupling resonant array is derivedbased on the equivalent circuit of typical WPT/MRC system and its optimumtransfer consideration. In this method, the input impedance is derived throughmutual inductance and the resonant array is predicted that the bandwidth can bewide if the array is reasonably arranged. Numerical simulation is conducted and theresults verify the theory well. The results show that the available transfer bandwidth of the resonant array can be at least twice as that of the typical WPT/MRCsystem with two resonant coils. In addition, one can observe that the magneticcoupling resonant array has steep band-edges, which means that the magneticcoupling resonant array has good performance of anti-interference. The simulationresults of different forms of arrays shows similar phenomena, meaning that theproposed method is universal for different forms of magnetic coupling resonantarrays.Next, the cause of frequency splitting phenomenon widely exsisting inWPT/MRC systems is analyzed through the expression of mutual inductance.Frequency splitting can be suppressed by eliminating the pole in mutual inductance.In this thesis, a method using a pair of non-identical resonant coils as transmitterand receiver is proposed to eliminate the pole of mutual inductance and obtainuniform mutual inductance versus transfer distance, and hence, frequency splittingcan be suppressed and stable and efficient transfer characteristics can be achieved.The proposed method is verified through analytical calculation, numericalsimulation and experiment test. The results agree with each other very well andvalidate the frequency splitting suppression ability of the proposed method. The experimental results shows that the transfer efficiency can be improved by6dB,and the variation of the transfer efficiency is within2dB. Compared with othermethods for frequency splitting suppression, the proposed method does not needsimultaneous impedance matching according to the transfer distance, and there is noneed to design control algorithm and the corresponding control circuits to track theoptimum transfer frequency of the WPT/MRC system.The research subject in this thesis is innovative and is researched by propermethods. The analysis in this thesis is comprehensive, and the results andconclusions will promote the development of WPT/MRC.