Key Technologies Of Distance-insensitive Wireless Power Transfer Based On Magnetically Coupled Resonant

Wireless power transfer(WPT)is a potential technology,which can be applied to the internet of things,medical equipment,consumer electronics,industrial robots,aerospace,and other electrical fields.Magnetically coupled resonant wireless power transfer(MCRWPT)has become a research hotspot in the field of wireless charging because of its advantages of long transmission distance,high power efficiency and low radiation.Considering that the MCR-WPT is a resonant circuit with high frequency,its circuit quality factor is very high.The change of position of electrical equipment will lead to drastic fluctuations of system parameters.Therefore,how to ensure the MCR-WPT system to adapt to the change of position is a key problem.In this dissertation,the coil structure,circuit topology and variable load of MCR-WPT system are studied.The purpose is to propose a comprehensive and effective design scheme to improve the load carrying capacity,power efficiency and stability of the MCR-WPT system.In addition,simplifying the control complexity of the system should be considered.Therefore,the main research work is as follows:(1)Design of coil structure.Taking the planar coil structure as the research object,the relationship between the change of position and the coil parameters(such as self-inductance and mutual-inductance)are analyzed.Considering the output parameters,the design goal is given which can reduce the sensitivity of the coil gain with the change of position.To this end,the characteristics of coil dimensions(such as coil shape,size,number of turns and wire pitch)with the change of position are analyzed,and the coil resonance matching point and center point are improved.Then,the coil design method and optimization process are proposed.On this basis,a large-small coil structure,one-to-two coil structure and one-to-four coil structure are designed for adapting to the change of position.The size of receiving coil is 60 × 60 mm,the distance between coils is 30 mm,and the diameter to distance ratio of coils is about 0.5.Finally,the large-small coil structure and one-to-four coil structure are manufactured and tested.The results show that the transmission power gain is more than 0.8 when the horizontal position changes within ±30 mm.(2)Design of circuit topology.Aiming at the problem of circuit detuning,the characteristics of output parameters(such as output current,voltage,output power and power gain)of WPT system are analyzed.To improve the load capacity and power efficiency of the system,a two-path self-matching topology based on planar four coil structure is proposed.The theoretical model of the circuit is established,and the traditional L-type matching topology is introduced as the comparison scheme.The transmission power gains of the proposed and the traditional scheme with different mutual-inductance are analyzed,and the power efficiency of the two schemes with the change of position are compared.The results show that the two-path self-matching topology can reduce the influence of position change on the load carrying capacity and power efficiency under the condition of constant operating frequency.Then,the design steps of component parameters of two-path self-matching topology are given.Finally,a prototype is developed,which has a working frequency of 6.78 MHz and a single coil size of 80 × 80 mm.The experimental results show that the maximum output power of the prototype is 50 W,and the power efficiency from DC to DC is about 72%-75%.Compared with the L-type matching topology,the range of position variation(horizontal direction: ± 20 mm,vertical direction: ± 15 mm)is increased by 100%.(3)Design of output stability.Aiming at the problem of output stability and considering the change of position,the correlation is analyzed between the variable load and the output voltage or current for the different compensation networks.It is found that the compensation networks have a loadindependent output characteristic within a certain range of coupling coefficient.Then,under the condition of different loads,the output voltage fluctuation of L-type matching network and two-path self-matching topology is analyzed,and the design goal of Buck voltage stabilization is given.To solve the problem of Buck voltage loss caused by excessive output voltage fluctuation,a rectifier design scheme based on impedance compression network is proposed.By establishing the theoretical model,it is proved that the impedance compression network can effectively reduce the influence of variable load on the input impedance.Finally,a WPT system with two-path self-matching topology and impedance compression rectifier is designed and verified.The results show that under the condition of different load resistance50 ? to 300 ?,the output voltage fluctuation rate of the proposed system is 39% with a range of position variation(horizontal direction: ± 20 mm,vertical direction: ± 10 mm).Compared with 77% of L-type matching network,the output voltage fluctuation rate of the proposed system is reduced by 49%.The dissertation provides an effective solution for distance-insensitive wireless power transfer.The given method can be applied universally to the analysis and design of MCRWPT systems.For example,it can be used for the design and optimization of parameters for planar coil structures,the solution of complex topological parameters using multi-objective parameter optimization algorithms,and the analysis of output characteristics for various compensation or matching networks.