Optimized Design Of Full Bridge DC/DC Converter Based On Silicon Carbide And Silicon Hybrid Switch

An increasing power density combined with a high functionality are demands on the present power converters,especially in aviation,aerospace applications.The recently emerging SiC devices provide a promising solution to improve the efficiency and power density of power converter by reducing semiconductor losses,operating at higher switching frequencies,higher temperatures and higher voltage in many different applications.However,the high material and fabrication cost of SiC power devices has limited its wide application and the current rating of SiC MOSFET still exists a large gap compared with Si IGBT.Parallel combination of SiC MOSFET and Si IGBT can be used to minimize switching and conduction losses,utilizing the low voltage drop of Si IGBT and low switching loss of SiC MOSFET.This thesis is dedicated to research on full bridge converter based on hybrid parallel devices.The static and dynamic characteristics of SiC MOSFET and Si IGBT are tested and compared at first.The differences of SiC MOSFET and traditional high voltage Si IGBT are listed.The output and switching characteristics of SiC MOSFET and Si IGBT are tested by double pulse test under variable working conditions and quantitative analysis is carried out.Based on the characteristics contrast of SiC MOSFET and Si IGBT,the optimized switching patterns of hybrid switch is proposed.The current sharing inside the hybrid switches is analyzed in steady state conditions by modelling.Considering the parasitic capacitance of SiC MOSFET and Si IGBT and the large amount of charges left in Si IGBT after its switching-off,the switching process of hybrid switch is analyzed in detail and then verified by double pulse test.The effect of delay time,load current and gate resistance on the switching characteristics of hybrid switch is investigated in the optimized switching pattern.Also,the switching energy of byrbid switch is compared with single Si and SiC device.Finally,a 2kW full bridge converter prototype based on bybrid switch is completed.The voltage,current waveforms of main working points are tested and analyzed.At the same time,a prototype based on Si IGBT is completed.The effect of hybrid switch to promote the efficiency of converter is verified.