Research On The Current Ratio Optimization Of Si IGBT And SiC MOSFET Hybrid Switch

In recent years,with the rapid development of new energy technology,electric vehicles and multi-electric aircraft,power electronic devices are gradually developing towards high frequency,high power density and high efficiency.The switching frequency of Si IGBT is more and more difficult to meet the requireme nts of high power density power electronic devices because of the physical characteristics of materials.Silicon carbide power devices represented by SiC MOSFET have become ideal devices for high frequency and high temperature applications because of their fast switching speed,low switching loss and high temperature resistance.However,due to the limitation of manufacturing technology,the manufacturing cost of SiC MOSFET at this stage is still high,and the current level is small,which can not meet the requirements of medium and high power applications.On this basis,the Si/SiC hybrid device combines the fast switch speed characteristics of SiC MOSFET and the low on-resistance characteristics of Si IGBT,which makes the hybrid device suitable for applications of medium-high frequency,large capacity and high power density.And the cost-effectiveness of hybrid can be further improved with a high-current Si IGBT as the main switch and a low-current SiC MOSFET as the auxiliary switch.This paper focuses on the optimization of current ratio of hybrid switch to provide theoretical basis for the selection of hybrid switch.Firstly,the operational principle and the switch modes of Si/SiC hybrid switch is described.A low-cost and high-reliability driving hardware circuit is designed according to the conduction characteristics of hybrid switch.The turn-on and turn-off process of Si/SiC hybrid switch are analyzed in detail,and the switching loss optimization method of hybrid switch is proposed.Secondly,the effect of current ratio of hybrid switch on device performances and device cost is analyzed.The loss mathematical model of hybrid switch and the thermal resistance mathematical model of SiC MOSFET which are based on chip area are proposed.The minimum current rating optimization algorithm of SiC MOSFET in hybrid switch is designed based on the above mathematical model.The minimum current ratio of hybrid switch under certain operating conditions is simulated and analysed.The effect of current ratio of hybrid switch on the performances of converter based on hybrid switch is simulated and analyzed experimentally.An evaluation method of the optimal current raito of hybrid switch based on the analysis of the cost and the converters' efficiency characteristics is proposed.A short-circuit test platform for hybrid switch is built,and the influence of current rating of SiC MOSFET on short-circuit reliability of hybrid switch is analyzed.Finally,a Buck converter platform based on Si/SiC hybrid switch is designed and built in this paper.The performances of Buck converter based on the Si/SiC hybrid switch,pure SiC MOSFET with the same current rating and pure Si IGBT with same current rating respectively are compared and analyzed.The great advantages of Si/SiC hybrid switch in improving the operational capacity and frequency of converters are analyzed.