| The Wireless Power Transfer Technology of Electric Vehicles can solve the problems of difficulty in charging,short life span and small battery capacity,which impede the development and popularization of electric vehicles.The DC/DC circuit on the energy receiving side of the system can match the battery voltage level;reduce current fluctuations,increase battery life,and improve system efficiency.However,it also brings defects such as low power density,high switching loss at high frequency,and low reliability.Therefore,this thesis designs a three-phase Interleaved Parallel Buck Circuit,and deeply studies the topology,soft switching characteristics and control strategy of the circuit.The main research contents are following:The overall structure of Wireless Power Transfer System is researched,and the topology of the system is determined.According to the requirements of the DC/DC circuit at the receiving side of the system,the analysis and design of the Three-Phase Interleaved Parallel Buck converter are emphatically carried out.According to the different working states of the converter,the basic principle of circuit is discussed.Based on the analysis of input and output ripple,the formula of minimum inductance and capacitance under any number of phases and frequency is proposed;The parameter design and selection of components are carried out.The soft switching technology and energy loss of the converter on the energy receiving side are analyzed.A soft switching method of Negative Valley Inductor Current is proposed.The inductance with a smaller inductor value is used to make the minimum value of inductor current negative,and the Turn-on loss with large energy loss in the switching process is replaced by the Turn-off loss with small energy loss,so as to reduce the switching cycle loss of high-frequency converter and improve the efficiency.The working characteristics of MOSFETs are analyzed through the simulation software,and the boundary conditions for realizing the soft switching are deduced.In addition,it is analyzed that the capacitor in parallel at the drain and source of MOSFET can further reduce the switching loss.Finally,the core loss is simulated and studiedThe control strategy of the converter is considered.Mathematical modeling analysis of the Interleaved Parallel Buck Converter is carried out,and a Double Closed-Loop PI control strategy of the voltage outer loop and the current inner loop is designed to ensure the control performance of the system.A Variable-Frequency Critical Soft-Switching control strategy based on PI control is designed.It is realized that under different working states of the wireless power transmission system,the converter can adjust the optimal frequency value to satisfy the soft-switching boundary condition and reduce the system loss.Research on MATLAB and Pspice simulation platform is conducted,and an experimental platform for testing and verification is built.The experimental results show that the Negative Valley Inductor Current soft switching method proposed in this paper can reduce the switching loss,and the Variable-Frequency Critical Soft Switching control strategy has good stability.Compared with the efficiency of large inductor buck converter,using small inductor can improve the efficiency of the converter by about 1.7%.To sum up,the three-phase Interleaved Parallel Buck converter proposed in this paper has effectiveness and advantages. |
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