Study On Magnetic Coupling Mechanism And Resonant Converter Technology In Wireless Power Transfer

Magnetic coupling wireless power transfer(WPT)technology has attracted much attention in power electronics field in recent years.Magnetic coupling WPT converters belong to loosely coupled resonant DC-DC converters.Modeling and parameter design of their magnetic coupling mechanisms and resonant converter topologies are key theoretical and technical topics.In this paper,the modeling of magnetic coupling mechanism is studied;and using the established models,three specific magnetic coupling WPT converter topologies are analyzed respectively,which involve their time domain modeling,resonant network parameter design,etc.The main research contents are as follows:1.Traditional concentric circular filaments cluster approximation model for air-core planar spiral coils does not consider the helicity,which produces an error.To overcome this disadvantage,analytical geometry is used to describe the shape of planar spiral coils,and the Euler Angle in classic mechanics is utilized to describe the relative position of the primary and secondray coils of the loosely coupled transformer(LCT),a mutual inductance accurate model for air-core planar spiral coils under arbitrary relative position is built,and using the geometric mean distance principle,a self-inductance calculation formula for air-core planar spiral coils is derived;the influence of the coil size and the relative position of the coils on mutual inductance is studied;combined with finite element simulation and experimental test,the difference between the accurate model of this paper and the traditional approximation model is compared(result shows,the relative error of the traditional method can reach 100% in the most unfavorable situation),and the reasonable radius of each turn of the traditional method is investigated.The design of magnetic coupling mechanisms with ferrite cores relies on finite element modeling and simulation.In the case of selecting the size of finite element modeling of planar spiral coils LCT with ferrite cores,when the mutual inductance and the distance and lateral misalignment are identical,the size of LCT with finite area ferrite cores should between that with air-core and that with infinity area ferrite cores,based on this principle,a method for preliminarily selecting the size of finite element modeling of ferrite-core LCT utilizing the analytical solutions of the ideal cases is proposed.The characteristics of the ferrite core solenoid and GU type ferrite core loose coupled transformer are studied by finite element simulation.2.At short range,abundant harmonics occur in the resonant network of SS compensated WPT converter,the fundamental harmonic analysis method(FHA)lacks of accuracy.By using the time domain method to overcome this disadvantage,the operation states and operation modes distribution of the converter are displayed,the output characteristics of the converter and soft switch characteristics in each mode are studied,and the boundaries of these modes are given.Experimental results of the prototype verify the accuracy of the time domain analysis.3.There are many degrees of freedom in the resonant network design of double sided LCC compensated WPT converters.To design the resonant network reasonably and efficiently,a method to determine the resonant network electrical parameters according to the constraints such as rated transmission power and switching frequency is proposed,which takes both harmonic current suppression and size of magnetic components reduction into account.A corresponding LCT design scheme is given: the size and turns of LCT are roughly estimated theoretically before finite element modeling,and then further optimized by finite element simulation.Experimental results of the prototype verify the feasibility of the proposed method.4.To serve short-range contactless power supply in harsh environments,a LLC resonant WPT converter based on the column-tubular core solenoid separated transformer is provided.In the traditional analysis and design methods of LLC resonant converters,FHA is concise but rough,while time domain method is precise but complicated.In this paper,based on time domain method,a PO mode gain formula and the operation mode boundary condition formula for LLC resonant converters are proposed,which are concise in form and easy to use.Experimental results of the prototype verify the feasibility of the LLC resonant WPT converter scheme,and the accuracy of the proposed formulas is demonstrated.