Research On Resonant Parameter Optimization Method For Electric-field Coupled Power Transfer Systems

Wireless power transfer(WPT)technologies are more convenient and safer than traditional conductive charging technology.Among them,capacitive power transfer(CPT)is becoming an attractive alternative because of their better misalignment performance and lower cost and weight.Electric-field resonance(EFR)compensation based six-plate CPT system is always one of the high-performance configurations,but the associated large number of circuit parameters is always a problem for the system design.In this paper,the resonant parameter optimization design methods are studied for high-stage EFR-based CPT system with the optimization target of transmission efficiency.The main research of this paper is described as follows:First,the basic modelling method of CPT system is studied including the modelling of capacitive coupler,compensation circuit,and the resonant network.The equivalent capacitance models and behavior-source models of the capacitive coupler are analyzed,and the coupling capacitance included in the resonant network are described together with the compensation circuit.The configurations of the resonant network and their output performance are proposed.Based on the first-order harmonic approximation(FHA)method,the ordinary equivalent linear resonant circuit models are analyzed.Based on the circuit models,a high-efficient CPT prototype is designed from the design of resonant network and hardware circuit,and the selection of power electronic devices.The circuit models and the prototype make the fundamental of the following research.To obtain the optimal circuit parameters of the CPT system,a genetic algorithm based global numerical optimization method is proposed.First,the nonlinear programming model of the CPT system containing variables,target function,and constraint conditions is given,based on which,an adaptive genetic algorithm combined nonlinear programming model is proposed for the parameter design.Based on the optimized parameters,the simulation verification is implemented by using LTSPICE,besides,associated experimental verification are implemented through the designed prototype.The results show that by using the optimized parameters that obtained by using the genetic algorithm,the efficiency can be effectively improved.But the results are always not the optimal parameters,which are scattered and needed to be further explained through the derivation of physical methods.To solve the disadvantages of numerical method which have complex result,unclear explanation and poor stability,a two-stage symmetric analytical optimal parameter design method based on minimum reactive power is proposed for the CPT system with EFR compensation circuit and six-plate coupler.In the first stage,the transferred power across the coupling capacitance C_S and the reactive power on C_S are optimized,and the constraint conditions for the parameter optimization are obtained.Based on these conditions,the reactive power of the system is simplified,and the complexity of the optimization problem is significantly reduced.In the second stage,the reactive power on the whole system is optimized to obtain the optimized circuit parameters.The optimized parameters are similar with that obtained by using the numerical method,and the reason why the results of genetic algorithm are scattered is explained.Based on the optimized parameters,the simulation verification is implemented by using LTSPICE,besides,associated experimental verification are implemented through the designed prototype.To solve the problem that the two-stage method is just suitable for the CPT system with symmetric structure,a universal global optimal parameter design method based on equality of reactive power that excited by two-point power sources is proposed.According to the performance of linear circuit,the independence of the reactive power that excited by independent voltage sources and the relationship between the transferred power and reactive power are analyzed.By setting the independent reactive powers as the variables,the high-stage parameter optimization problem then be changed to a two-stage optimization problem that only have two variables.By using this method,the optimization problem can be significantly reduced,and the optimal parameters can be easily obtained.Based on the optimized parameters,simulation verification is implemented by using LTSPICE,besides,associated experimental verification are implemented through the designed prototype.As described above,to solve the nonlinear optimization problem for parameter design of CPT system with EFR compensation circuit,the global optimization methods are studied in this paper from numerical and analytical perspectives.The effectiveness of these methods is verified and the improvement of the system efficiency is obtained through simulation and experimental verification.The studies in this paper provide valuable reference for the optimal parameter design of the CPT system with other circuit structures.