Research On A New Type Of Silicon Carbide Device LLC Resonant Converter

In this dissertation,a new type of SiC device LLC resonant converter with high frequency,high efficiency and low loss is designed for the charging power system of electric vehicle charging pile.The converter can be applied to the charging power module of charging pile.First of all,the advantages and disadvantages of different circuit structures are compared and analyzed,and the LLC resonant converter is selected.LLC resonant converter has the advantages of simple circuit structure,high switching frequency and high power density.Then,the working principle and working process of the LLC resonant converter at different operating frequencies are discussed in details,and the suitable operating frequency is selected.The two necessary conditions for the converter to achieve soft switch technology are analyzed.By studying the principle of First Harmonic Approximation,the FHA equivalent circuit of LLC resonant converter is analyzed,and a reliable and effective design scheme of LLC resonant converter is proposed,and the influence of different parameters on the performance of the converter is discussed in depth.In the case of high frequency applications,the switching stress and switching losses of the LLC resonant converter become increasingly prominent.A number of new technologies have been proposed to improve power density while reducing the switching stress,switching losses and improving power conversion efficiency.Among them,the application of soft-switching technology is the most prominent.On the other hand,begin from the power electronic devices,compared with silicon semiconductor power electronic devices,wide bandgap semiconductor power electronic devices have high operating frequency,high blocking voltage and strong high operating temperature tolerance,but also have the advantages of lower switching losses and on-state resistance,which makes it in the converter will inevitably show great application potential.In the wide bandgap semiconductor power electronic devices,the new silicon carbide devices as the representative.In this dissertation,combining with the new silicon carbide device,explores its static characteristics and dynamic characteristics,the SiC devices and Si devices with similar rated power are selected to analyze and compare the characteristics.At the same time,this dissertation sets up the simulation model of double pulse test circuit,the simulation test is carried out and the theoretical verification results are given.This dissertation summarizes the incomparable superiority characteristic,application advantages and development potential of SiC devices in the field of high power,high voltage and high frequency power electronic applications.In this dissertation,SiC MOSFET,SiC SBD,respectively,are used as the main switches and rectifier diodes for the LLC resonant converter.According to the practical application requirements,the parameters of the LLC resonant converter based on the SiC device are determined.Meanwhile,according to the switching characteristic of the SiC MOSFET,the control circuit and the driving circuit of the SiC MOSFET are designed and the corresponding circuit schematic diagrams are drawn.Finally,the simulation model of the converter is built in the LTspice simulation software and the circuit board is tested.The results show that the correctness of the theoretical analysis and the feasibility of the parameter design scheme are verified.Considering the practical application of the problem,analysis and research the loss of the LLC resonant converter,using different SiC devices and Si devices as the converter switching devices to form a number of test groups,focusing on the loss caused by switching devices.The results are given clearly with data and graphs.It is proved that the choice of SiC devices can effectively reduce the loss and improve the efficiency of the converter.