| Wireless Power Transfer(WPT)is a widely used at present.With its flexible,convenient and green characteristics,WPT has broad development prospects in consumer electronics,electric vehicles,transportation and other fields.However,with the continuous improvement of operation power and frequency level,the switching loss of the high frequency inverter of WPT system will increase,which will reduce the transmission efficiency of the system.Using the soft switching characteristic of Pulse Density Modulation(PDM)is an effective way to reduce the loss of high frequency switching,but the traditional PDM is a discontinuous graded modulation method,causing current oscillation,output voltage ripple increase,output power discontinuous graded regulation and other problems.This paper studies and analyzes these problems,mainly including:Firstly,based on the traditional PDM technology and Phase Shift Modulation(PSM),a hybrid Modulation method combining the characteristics of PDM soft switch and PSM stepless Modulation was proposed.In this method,the traditional PDM full-wave energy injection mode is disassembled and transformed into half-wave energy injection mode,which can effectively suppress the current oscillation and output voltage ripple modulated by traditional PDM.On the basis of this,a half wave in PDM sequence is controlled by phase shift to realize the continuous adjustment function of the inverter output,while preserving the soft switching characteristics of traditional PDM to a large extent,and the effectiveness of the hybrid modulation method is verified by simulation analysis.Then,by establishing the state space model of WPT system,combining with circuit theory,the energy transmission mechanism of WPT system is analyzed,and the main existing power loss and its improvement methods are analyzed.On this basis,a bilateral control strategy of WPT system based on improved PDM modulation is proposed,in which the primary side adjusts the output voltage and the secondary side performs impedance matching to achieve the optimal efficiency tracking and voltage stabilizing control under load change.The effectiveness of the strategy is verified by simulation analysis.Finally,the improved PDM modulation method and the optimal efficiency tracking strategy are verified based on the WPT experimental platform.The results show that the improved PDM modulation method has both stepless regulation and soft switching characteristics,and the current oscillation and output voltage ripple are smaller than the traditional PDM.The improved PDM modulation bilateral control strategy can effectively track the optimal system efficiency within a certain range of load variation. |
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