Research On Key Technologies Of Electromagnetic Induction Based Wireless Power And Data Transfer Under Conditions Of Varying Couplings

Wireless power transfer(WPT)provides the advantages of flexibility,convenience,galvanic isolation,free maintenance,and weather proofing.Hence,it could be employed in aeronautics and astronautics,electric vehicles,biomedical implants,consumer electronics,and smart homes.WPT has attracted plenty of attention from both the academia and industry.Nevertheless,the problems such as many compensation components,poor misalignment tolerance,low power transfer efficiency(PTE),and high system cost,are hindering the industrial application of this technology.The general design rules of compensation topologies have not been summarized although many compensation topologies have been proposed.This dissertation analyzes the voltage-current and impedance transforming characteristics of four fundamental resonant tanks.The design rules of compensation topologies were summarized subsequently.A current-fed load oriented compensation topology LC/S,whose output current is irrelevant to the load,was proposed according to the design rules.According to the influence of the coupling inductances on the normalized stresses,the coupling inductance design method was proposed.The normalized component stresses of the LC/S compensated WPT system are within reasonable ranges by using this method.A voltage-fed load oriented compensation topology S/CLC,whose output voltage is independent of the load,was proposed according to the design rules summarized before.Both LC/S and S/CLC show the characteristics of less compensation components,lower component stresses,and near-zero input impedance angles.The system cost is reduced,and the power transfer efficiency is improved.The rightness of previous theoretical analysis was validated by a series of experiments.Most WPT systems are coupling-varying wireless power transfer(CV-WPT)systems.The reported parameter tuning methods are not applicable to CV-WPT systems.To reduce system output ripple versus the coupling,this dissertation proposed a particle swarm optimization(PSO)based parameter tuning method for CV-WPT systems.The tuning of compensation parameters was transformed into a multi-objective optimization problem.The optimization objective consists of the variance of output voltage,the currents flowing through the compensation and coupling inductors,and a punishment function for hard switching operation.The compensation parameters in the case of the average coupling coefficient are firstly calculated using the conventional parameter tuning method.Then,a proper scaling factor is selected to obtain the solution space.Finally,the maximum and minimum particle velocities are computed by equally dividing the solution space.The proposed parameter tuning method can minimize the output voltage ripple under the premise of a passable PTE and ZVS operation in full operating range.Two WPT prototypes,one designed by the conventional parameter tuning method while the other designed using the proposed method,were built.The validity of the proposed parameter tuning method was demonstrated by performance comparison.The misalignment tolerance of a WPT system can be improved by optimizing the compensation parameters,but the improvement is limited.In order to further enhance the misalignment tolerance,a novel unsymmetrical coupling structure(UCS)based on concentrated magnetic flux was proposed.The magnetic flux of UCS concentrated on the center region,resulting in excellent misalignment tolerance.The decrease gradient of PTE is much smaller than that of the coupling coefficient.Therefore,the PTE of the WPT system using UCS is quite high.In order to obtain the optimal misalignment tolerance in the case of given space and preset coupling coefficient,the impact of the size-related parameters,such as primary winding height,primary winding width,primary ferrite width,secondary winding height,and secondary ferrite height,on coupling coefficients and coupling retaining ratios was analyzed using finite element analysis(FEA)simulation.The optimized parameter design method was proposed,based on which the coupling coefficient and the misalignment tolerance of UCS are good.For the purposes of closed-loop control,user identification,condition monitoring,and data transfer,the necessary data needs to be transferred between the primary and secondary sides of a WPT system.The reported wireless power and data transfer(WPDT)schemes show the drawbacks of low data rate,strong crosstalk,and low reliability.This dissertation clarified the essential reasons of these drawbacks.A novel WPDT scheme based on amplitude-shift keying(ASK)and capacitive coupling was proposed as well.Due to parallel connection of power circuit and data injection and extraction circuits in the proposed scheme,the impact of power transfer on data transfer is minor,and the PTE is high.The filtering performance of several symmetrical compensation topologies was analyzed.Double-sided LCC provides the optimal overall performance.Hence,it is selected as the compensation topology of the power circuit.Two trapper inductors were introduced to change the impedance of the carrier path,improve data transfer gain,and reduce the complexity of data demodulation.A WPDT prototype,whose output power was around 100 W,was built.The measured PTE and data rate of the prototype are 90.5% and 119 kbps,respectively.