Research On The Effect Of Threshold Hysteresis On The Switching Characteristics Of SiC MOSFET

Among many power electronic devices,SiC MOSFET has been applied in UHVDC transmission,electric vehicle and other fields because of its excellent high frequency characteristics,high temperature characteristics and high speed switching characteristics.However,due to the inherent high interfacial state density of SiC/SiO2 interface,threshold hysteresis has always affected the threshold voltage stability of sic MOSFET.Therefore,to improve the reliability of SiC MOSFET.,the research of the influence of threshold hysteresis on the switching characteristics of SiC MOSFET is significative.In order to quantitatively evaluate the influence of threshold hysteresis on the switching characteristics of SiC MOSFET,this paper takes switching delay time and switching loss as the key switching transient parameters.Besides taking the rise and fall time of driving voltage into consideration,this paper optimizes the shortcomings of existing models to establish a switching transient model of SiC MOSFET considering threshold hysteresis.Compared with the existing switching transient model,this model is more consistent with the actual working conditions,and describes the switching transient process more accurately.At the same time,the analytical expressions of switching transient parameters conforming to IEC standards are obtained.Secondly,double pulse experiments under different driving negative pressures are carried out at room temperature and switch delay and switch loss are extracted.By combining the experimental results with the analytical model,the accuracy of the switching transient model and the switching transient parameter expression is verified,and the influence of driving negative pressure and threshold hysteresis on the switching characteristics is decoupled and quantified.The results show that,both driving negative voltage and threshold hysteresis will reduce the opening delay time,but the influence of threshold hysteresis is much greater than that of driving negative voltage.Driving negative voltage has no influence on opening loss.The threshold hysteresis instead of driving negative voltage will lead to the reduction of opening loss.Then,considering that high temperature will weaken the threshold hysteresis effect,this paper combines theoretical analysis with experimental verification.The influence of threshold hysteresis on switching transient parameters at high temperature is decoupled and quantified.When the driving negative voltage decreases,the threshold voltage reduction rate slows down at high temperature.Therefore,the reduction rate of opening delay and opening loss will slow down with the decrease of threshold voltage.The influence of threshold hysteresis on switch transient parameters is still obvious.At the same time,with the lower the driving negative voltage,the weakening effect of high temperature on threshold hysteresis and its influence on switching characteristics will gradually become stronger.Finally,since it is difficult to directly measure the threshold voltage subject to the threshold hysteresis effect during the opening process,based on the analytical expression of the opening delay conforming to IEC standards,this paper proposes a calculation method to obtain the opening threshold voltage under a specific driving negative voltage,and obtain the relationship between the drive negative pressure and the threshold voltage considering the influence of the threshold hysteresis.The accuracy of this method is proved by experimental results.