Voltage Optimization Of Passive Resonant Elements In Electric Field Coupled Power Transmission System

Wireless power transfer technology is a brand-new electric energy transfer technology that delivers electric energy from the power transmitting side to the power receiving side through an indirect electric connection by magnetic field,electric field,laser,microwave,etc.It eliminates the inherent defects of the traditional contact power supplies.The capacitive power transfer(CPT)based on the electric field coupling method uses high-frequency alternating electric fields to transfer energy.It only uses thin cheap aluminum or copper plates as the transmitters or receivers.CPT is also beneficial in that the leakage electric field will not cause eddy current loss with the existence of surrounding metal objects.CPT has good robustness to directional misalignment and unique advantage in dynamic power supply and electric vehicle charging,which has gradually drawn great attention of research teams at home and abroad.This paper focuses on the research of CPT circuit topology and the optimization of the voltage stress of passive resonant components.First,the study investigates the equivalent structure,equivalent capacitance,capacitance change rate,and transmission capacity and radiation range of three different coupling mechanisms(horizontal,vertical,overlapping coupling)by combining theoretical calculation with MAXWELL finite element simulation.In order to address the problems in the LC series topology,such as low level of receiving power,short transmission distance,and the problem of excessive components in double LCLC topology,an analysis of two common topologies of CPT system in this study.Then a simpler CLLC-L topology is proposed with inherent constant output voltage characteristic by simplifing the original topology via the Y-? transform,making it an equivalence to the cascaded CLC-LCL resonant networks.In capacitive power transfer system,the passive resonant components often bear a large voltage due to its small coupling capacitance and its high operating frequency.Especially at its maximum power point,high-level voltage may break down components and result in system detuning,and even cause safety problems.In order to overcome this problem,this paper presents a method to optimize the voltage of passive resonant elements.This method,based on the CLLC-L topology,achieves the optimized voltage of the passive resonant elements by reasonably configuring the parameters of the passive resonant elements.Based on the proposed method,this paper designs a capacitive power transmission system with transmission distance of 150 mm and equivalent coupling capacitance of only 13 p F.When the transmitting power reaches 2.12-kW,the DC–DC system efficiency is up to 89%.The coincidence between the experimental voltage and the calculated voltage shows that the voltage optimization method can effectively lower the voltage stress of the passive resonant elements.This method improves the safety margin of the system.