Study On Topologies With Constant Output Voltage Or Current For Electric-field Coupled Power Transfer Systems

Electric-field coupled power transfer(ECPT)technique uses high frequency electric field as energy medium to transfer power Wirelessly.It features low cost,high design flexibility of the coupling interface,low electromagnetic interference(EMI),and the ability to transfer power through metal barriers.Nowadays,it has attracted increasing attention from researchers.In the practical application of ECPT systems,some electric equipment requires a constant output voltage or a constant output current to keep its operation in a normal state.For some others,not only the two modes,but also the flexible switching between the two modes are required.Moreover,some applications require multi-supply of ECPT system to electric equipment with the previous characteristics.Based on the demand of the three kinds of ECPT applications,this paper uses two-port network theory to analyze constant output characteristics of two-order,three-order and four-order resonant network,and further proposes three different kinds of topologies.Without extra communication versus control circuits,the proposed topologies can ensure constant voltage or current regardless of the variations in the loads,maintaining the system in a ZPA state with intensive harmonic suppression and robustness of parameters.Focusing on the existing variety topologies of resonant networks,two-port transmission parameter models for resonant networks are built.The constant-voltage or constant-current output conditions for voltage-controlled-voltage,voltage-controlledcurrent,current-controlled-current,and current-controlled-voltage resonant networks are derived.The parameter relationships for second-order,third-order,and forth-order constant-output resonant network are resolved.Based on the parameter relationship,circuits with constant-output are presented.To solve the problem that resonant networks' output characteristics are sensitive to parameter variations,the ECPT systems' voltage gain model for reversed -T resonant network are built based on impedance conversion.The influence rule of load quality factor,inductance ratio,and capacitor ratio on systems' voltage gain are analyzed.Both the voltage gain model and parameter interval are verified by the simulation and experiment.The parameter conditions for constant-output two-port networks and analysis on the sensitivity of resonant networks' parameters are theory foreshadowing for building subsequent topologies.The paper gives a circuit topology based on T-? mixed-resonant net which aims at application that need EPCT system has a constant output voltage for only one load.It achieves that system output voltage keeps same when the load changes and always works in ZPA state.According to branch reactance character of ?-CLC and T-LCL net,this paper sets up two net transport models and analyzes the impedance character,output gain and condition that ensuring constant output in different parameter configurations.Studying the rate of total harmonic distortion of ? and T net in different parameter configurations.Then giving a parameters configuration method which has the lowest distortion rate of inverter current and rectifier bridge input voltage.What's more,this paper analyze the resonant net impedance character under the influence of resonant frequency and quality factor and gives the load changing range under the giving output voltage deviation ratio.Based on the front analysis,giving the system parameter design method which has a better comprehensive performance.Finally,the constant output character of system,the ability of harmonic suppression and the accuracy of the parameter design method are verified by simulation and experiment.In some practical applications,the switching between constant output voltage and current is required.An ECPT system with F-F/T changing-topology resonant networks is proposed to meet this requirement and the reliable switching between constant-voltage mode and constant-current mode is achieved.Based on the approximation theory of fundamental wave and the impedance characteristic of the networks,the transmission models of the networks are built.For the F-LCLC and F-CLCL networks,both the output gain and the circuit parameters which can maintain the output voltage are discussed.Furthermore,the sensitivity of the input-impedance characteristic of these two networks under the variations of the system operating frequency and the quality factor is analyzed.The transfer characteristic of T-CLC network is analyzed,based on which the condition of constant current is obtained.By combining the characteristics of the third-order T network and the fourth-order F network,the switching method of T-CLC and F-CLCL networks is proposed and the value of the parallel capacitance is calculated.On this basis,the allowable load variation of the above-mentioned systems are investigated and the circuit parameters design flow is given.Finally,the constant-voltage/constant-current output characteristic of the proposed system,the effectiveness of the switching between constant-voltage mode and constant-current mode,and the feasibility of the parameters design method are validated by simulations and experiments.On account of the multiple pickups applications in which the ECPT systems are required to have constant voltage output,constant current as well as voltage output,and non-constant output,we present an ECPT system using F-LCLC resonant circuit at primary side and using corresponding resonant circuit for different needs at secondary side.Also we present the configuration method for the system parameter and the resonant regulation control method for the coupling mechanism.This system and its control methods achieve the function that random switching load does not influence the constant output characteristic of other load.On the basis of Fourier series expansion,we get the input harmonic current expression of the F-LCLC resonant circuit at primary side on no load situation and get the changing rule of the ratio of harmonic current amplitude and fundamental wave current amplitude corresponding to harmonic order number.Then we present the stepless-resonant regulation circuit of the coupling mechanism and build the equivalent inductance mathematical model introducing its resonant regulation control method in addition.According to transmission characteristic of resonance circuit,we give out the design method for system parameter.Finally we verify the accuracy of the system parameter design method and the constant output in random switching load situation.