Research On Modeling And Control Of Multi-Load Magnetically Coupled Resonant Wireless Power Transfer System With Varying Spatial Scales

With the rapid development of science and technology,various kinds of electronic devices such as smart phones,iPads,etc.,are becoming popular in daily life.It is urgent to provide green,safe and stable wireless power supply to multiple electrical equipment simultaneously.In recent years,magnetic coupled resonant(MCR)wireless power transfer(WPT)system has attracted increasing attention due to its advantages of high efficiency and high-power transmission in long-distance applications.At present,the research on multi-load MCR WPT mainly focuses on the maximum power/efficiency transmission.However,in different applications,the spatial misalignment between the transmitting coil and the receiving coil will exert an influence on the transmission characteristics of system owing to time-varying mutual coupling between coils.Taking a double-load system for example,an equivalent circuit model of single-frequency double-load MCR WPT system under different spatial misalignments is established in this thesis.Based on fundamental harmonic analysis and equivalent circuit theory,the influence of spatial scales on the transmission power and transmission efficiency is analyzed in detail.The mutual inductance between the transmitting coil and the receiving coil in the general case is calculated to find out the tendency of the transmission characteristics of the system under different spatial scales.But the single-frequency multi-load system can only transfer power for multiple loads with energy of single frequency at any time even if the operating frequency of the system is adjustable.Besides,it is impossible to identify multiple loads effectively.Therefore,the concept of multi-frequency is proposed in multi-load system to solve the above problems.In multi-frequency systems,the different spatial positions of receiving coils also have an influence on the transmission characteristics of the system.Taking double-frequency double-load system as an example,this thesis focuses on the transmission characteristics of the system under different spatial scales.To attenuate the fluctuations of transmission power on receivers with variable spatial scale,a multi-frequency control strategy based on pulse density modulation(PDM)is proposed in this thesis.When the spatial scales of coils change in a specific range,the system can maintain constant output voltage by adjusting the pulse density of the driving voltage of switches.The experiments of the single-frequency double-load MCR WPT system and the double-frequency double-load MCR WPT system are carried out and the results agree with the theoretical analysis well.As shown from the detailed experimental results,the system can effectively achieve constant output voltage on loads and power distribution among multiple loads by introducing PDM control.