Basic Research On The Wireless Power Transfer System Of Cordless Kitchen Appliances

Wireless power transfer is a non-contact power supply method with advantages of safety,reliability and stability.It has important research and application value in the field of kitchen appliances.However,with the increasing variety and number of kitchen appliances,the general purpose designing of coupling structures and compensation topologies are facing challenges.Therefore,this thesis takes the system of cordless kitchen appliances as the research object,carry out theoretical and experimental research on the transfer characteristics and stability of various coupling structures,output load characteristics and frequency domain characteristics of various compensation topologies,human safety in the electromagnetic field,together with the optimized design of related materials and structures.In order to solve the output compatibility issues of different coupling structures based on cordless kitchen appliances,this thesis has analyzed transfer characteristics of various structures separately,and has proposed stability criteria of corresponding systems.Firstly,the equivalent circuit models based on mutual inductance of different structures are established,and the expressions of output power and transfer efficiency are given respectively.In order to achieve the steady output power of each load with different structures,the judgment conditions of matching system parameters are derived,and the parameters that affect the transfer efficiency of under this condition are analyzed.Meanwhile,to realize the steady power output or maximum transfer efficiency,the design expressions of load impedance in different systems are derived,and the method of parameter optimization is also proposed.Secondly,in order to avoid the instability during the power transfer,i.e.,the frequency bifurcation,the stability conditions of different structures are derived,and the related stability judgment conditions are also given,which lays a theoretical foundation for the design of load parameters corresponding to various types of coupling structures.Focusing on the various loading of cordless kitchen,general conditions for the output characteristics of the resonant circuit topology are proposed: constant resonant current at the primary side,load-independent voltage(LIV)output,zero angle phase(ZPA)input,and unit voltage gain.The time domain and frequency domain characteristics of different resonant compensation topologies are analyzed,and pointed out that LCC-S is a compensation topology with strong versatility and simple design.Firstly,by classifying the load characteristics in the cordless kitchen,and analyzing the corresponding system output characteristics,this thesis have proposed the output conditions of the compensation topology suitable for the cordless kitchen.Secondly,the output characteristics of eight resonant circuit topologies under the conditions of LIV output are analyzed,which indicates that LC-S,LCC-S and LC-CL compensation topologies could meet the conditions.In addition,by establishing the corresponding transfer functions,the conditions for satisfying the LIV output and zero reactive power simultaneously are given,and the analytical relationship between the LIV output frequency point and the voltage gain of various compensation topologies is derived.Meanwhile,the output power thresholds of different source levels are compared.The results indicate that LCC-S compensation topology satisfies the conditions of general purpose designing,with simple structure and high output power,which is suitable for tailess kitchen appliances.According to the safety of the cordless kitchen electric emission source,this thesis takes ICNIRP 2010 as the safety reference standard of this theiss,by analyzing the reference limit and basic limit requirements of different international safety standards.This paper has also established simulation models of the human body in the environment with cordless kitchen system,and has revealed the influence law of the surrounding electromagnetic field on the human body.Firstly,in order to clarify the frequency and value range of different safety standards,four authoritative safety standard limit requirements are compared,and the mathematical model of the basic limits under different standards is given.Secondly,the human body model exposed in the electromagnetic field from single-coil transmitter and multi-coil transmitter coupling structures is established.The relationship between basic internal limits and external reference limits under different power,frequency,distance and coil combinations is analyzed.It reveals the influence law of different basic limits and reference limits in safety standards,which lays a foundation for the design of safety for cordless kitchen appliances.Finally,by simulating the standing position of the human body,the experiment is carried out to measure the data of cordless kitchen electric emission source in the space of the electromagnetic field,which indicates that the measured data is basically consistent with the simulation analysis result.In order to reduce the producing cost of cordless kitchen appliances and the influence of electromagnetic radiation and improve the transfer efficiency of the system,this thesis have presented optimal design methods from the point of copper loss,magnetic loss,coupling structure design,and shielding design,respectively.An experiment setup for cordless kitchen appliances is built,to verify the output characteristics of compensation topologies at the primary side,and the characteristics of coupling structures.From the point of material design and selection,the optimization methods of wire and magnetic material are presented.The simulation model based on finite element of coupling structure and shielding is established and the corresponding design method is obtained.Two experiment setup for cordless kitchen appliances with optimized LCC-S compensation topology,and with large transmitteris and small receivers are built to verify the theoretical results of compensation and coupling structures.The experimental results indicate that the designed resonant compensation topology could meet the output requirements of various loading;The universal design of coupling structure could maintain constant power output within a certain range of the transmitting coil surface,thus the accuracy of the theoretical model is verified.