| Wireless power transfer(WPT)system has become a hot research topic in recent years and has been applied in intelligent products and electric vehicles.To meet the smaller converter size,WPT has been operating at the megahertz level.The high frequency means that the theory at low frequencies needs to be further optimized,and the effects of more parasitic parameters need to be considered.Based on the magnetic coupled resonant WPT(MCR-WPT)system,this thesis improves the transfer efficiency of the system by optimizing the Class-E rectifier.The basic schematic of the MCR-WPT system is introduced in this thesis,and the topologies commonly used for each schematic are listed.By comparing the performance and applicability of various topologies,it is determined that the Class E topology is used for rectifier and inverter,the LCC-S topology is used for compensation network,and the double coil coupling structure is used for coupling structure in this thesis.For the high-frequency rectifier,the thesis introduces the mathematical model of the Class-E rectifier with finite output inductance.Since the input impedance of the rectifier is not a pure resistance,it cannot match the inverter perfectly.Therefore,based on the Class-E rectifier with finite output inductance,an optimal design of the Class-E rectifier with near resistive input is proposed.Through this optimization method,the phase of the input impedance of the Class-E rectifier can be reduced so that the input impedance of the rectifier can be as close as possible to the resistance,and the reactive power demand of the system can be reduced so as to improve the transmission efficiency of the system.Then an experimental prototype of a Class-E rectifier working at 6.78MHz is designed.By comparing the input impedance of the rectifier before and after optimization,it is found that the phase of the input impedance can be reduced by half through the near resistive input optimization design.For the planar inductor,the output inductor of the Class-E rectifier is optimized in this thesis.Planar inductors are widely used in the market for their advantages of good heat dissipation,easy and mass production,and higher power density.In this thesis,the planar inductor is used to replace the winding inductor,and the winding layout is optimized to reduce the wingding loss.In the end,the optimal case with minimum loss is obtained through finite element analysis and measurement.Finally,an experimental prototype working at 3MHz is built to verify the optimal design of the planar inductor and near resistive input impendence.It is mainly composed of a push-pull Class-E inverter,a push-pull Class-E rectifier,and a coupling structure.Through experiments,the relationship between the input impedance of the Class-E rectifier,output inductance,and diode voltage waveform with load change,the harmonic content of output inductance current,and the enthusiasm diagram of the planar magnetic element are analyzed.The peak efficiency of the Class-E~2 prototype reaches 85.73%after optimization. |
