| As an innovative technology,wireless power transfer(WPT)is capable of delivering power in a contactless way,which offers remarkable characteristics of safety,reliability and flexibility compared with the traditional power transfer.In recent years,WPT technology has attracted unprecedented attention in electrical engineering,and it has shown great potential in various practical applications,such as portable electronic devices,implanted medical equipment,electric vehicles,and so forth.However,the WPT technology is still in a development stage and suffers from some intractable problems,including low transmission efficiency,resonance frequency drift and unstable output control.Besides,with the rapid development of WPT technology,there is a growing number of the electrical devices supporting the WPT technology.Under such circumstances,with the application of multi-transmission system,the transmission power and location of each transmitting system can be flexibly configured,to overcome the bottleneck problems such as uncontrollable charging coils and low receiving power when the coils misaligned in the single transmitting system.Therefore,the multi-input and multi-output(MIMO)WPT technology will be more promising in the future application scenarios,and the MIMO WPT system will become a general development trend in the future.However,in MIMO WPT systems,the destructive interference between multiple transmitting coils and receiving coils brings a serious impact on transmission power and efficiency.In this regard,to promote the further development and practical applications of WPT technology,this dissertation focuses on coil optimization、circuit design and control strategies in low-power WPT system.Specifically,the main research works are summarized as follows:1.An optimized coil with variable winding width for improving the transmission efficiency is proposed.By analyzing the coupling circuit of a WPT system,the influencing factors of transmission efficiency are determined.Considering the coil structure,coil shape,turn-to-turn distance,coil width and width variation mode are set as the optimization variable,and the variable constraints are established.Using the finite element analysis and genetic algorithm,a prototype coil is designed and manufactured based on the simulation results.A WPT experimental platform is constructed to verify the better transmission performance of the optimized coil.2.The multi-objective frequency tracking and controlling methodology based on the maximum received voltage and the maximum transmitting efficiency is proposed.From the monitored variations of the load voltage at the receiving end and the input power at the transmitting end,the source exciting frequency was constantly updated to tune the system in the maximum power transmission state or the maximum efficiency transmission state,improving the transmitting power and efficiency of the system.The control circuit is then designed and the control software is developed to realize a precise control of frequency.A wireless power transfer prototype is constructed,and the fixed frequency experiment and frequency tracking experiment are conducted to verify the effectiveness of the proposed control method.3.The online voltage phase synchronization in receiving coils of multi-input WPT is proposed.In multi-input WPT systems,it is plagued to create a destructive interference between the multiple transmitters to result in a relatively low voltage delivered to the receiving coil and load,due to the phase differences of the received voltages from different transmitters.In this regard,it is essential to synchronize the phases of the received voltage of the receiving coil from different transmitters.However,the existing offline synchronization methodologies rely heavily on an analytical form solution of the received voltage in a receiver.To eliminate these deficiencies of existing synchronization methodologies,an online synchronization methodology is proposed for a multiinput WPT system.In the proposed methodology,the received voltages from different transmitters are determined from a series of online voltage sampling under different offset phases,and a synchronization strategy is then proposed.A multi-input WPT prototype is developed to test the feasibility of the proposed synchronization methodology.The experimental results have demonstrated that the received voltage is significantly enhanced by applying the proposed online phase synchronization methodology.4.The voltage control methodology to optimize the transmission efficiency of a multi-input and multi-output WPT system is proposed.In this paper,a simple multi-port network model is introduced to simulate a MIMO system to avoid the complex circuit topology and a large number of circuit elements.According to the multi-port network model,the expressions for the corresponding system parameter in terms of the transmitter voltages are derived.On this basis,a voltage control strategy to maximize the transmission efficiency of a MIMO WPT system by controlling the amplitude and phase of the transmitter voltages is proposed.To validate the proposed model and voltage control methodology,a 3-input and 3-output WPT prototype is designed and fabricated,and used as the experimental platform.The performances of the proposed voltage control methodology are compared to both the experimental ones and those without the proposed voltage control methodology. |
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