Research On Series Connected SiC MOSFETs Modeling And Driving Technology

Recently,the technology of power electronics has been getting developed greatly,and has been becoming an important role in power industry.The power electronics equipment has been more and more common in power system,especially under the situation of increasing grid-tied new energy converters and application of flexible AC,DC power transmission.As the core of power electronics converter,the parameters of power semiconductors will influence the performance of the converter directly.Now,the silicon based power semiconductor devices,which consists insulated gate bipolar translator(IGBT)and metal oxide semiconductor field effect transistor(MOSFET),has experienced decades of development and research,and its performance has approached its physical limitation.In order to realize better performance,people has paid attention to wide band-gap material,which mainly includes silicon carbide(SiC)and gallium nitride(GaN).Silicon carbide semiconductor power device is one of the third generation power electronic devices,which has great advantage over traditional silicon devices.Silicon carbide material has higher breakdown electric field intensity,faster electron saturation velocity and better thermal conductivity.These advantages give silicon carbide power devices higher rated voltage,faster switching speed,and lower switching losses.Silicon carbide MOSFET is the most representative one among all kinds of silicon carbide power devices.Although the application of silicon carbide material has increased the rated voltage of MOSFET greatly,now the commercial available silicon carbide MOSFET rated voltage can only reach 1700V,which limits its application in distribution power network and new energy converter.In this way,the direct series connection technology has been put out to overcome voltage shortcoming.The fast switching transient has set barrier for the utilization of series connected silicon carbide MOSFET.In order to use series connected silicon carbide MOSFET better,this thesis has focused on several problems as follows:(1)The advantages of silicon carbide power devices and its application have been analyzed.Different types of silicon carbide power devices have been introduced.Also,the direct series connected silicon carbide MOSFET model and its driving technology are reviewed.(2)The circuit model of power silicon carbide MOSFET is analyzed,the piecewise linearization method for junction capacitance is discussed,and the influence of the parasitic inductance is evaluated.Also the test circuit of series connected silicon carbide MOSFETs is presented and its components are introduced.(3)The voltage rising transient of series connected silicon carbide MOSFETs is discussed qualitatively,where the effects of the nonlinearity of junction capacitance and the existence of freewheeling diode junction capacitance are emphasized.Based on qualitative analysis,the voltage rising transient is analyzed quantitatively.The expression of voltage slew rate is calculated and deduced.In addition,the phenomenon of channel current dropping to 0 during the turn off transient is pointed out,and the influence of this phenomenon is also discussed.(4)An active delay control method based gate driver has been proposed,which uses delay line IC for delay action.The circuit can adjust drive signal by a step of 0.15ns,and with closed-loop control strategy,the driver can balance the voltage of series connected silicon carbide MOSFETs effectively.The basic idea and design consideration of the driver is introduced in detail.(5)In order to verify the analysis of series connected silicon carbide MOSFETs voltage rising transient and the active delay control method based gate driver in this thesis,two experimental platforms are established,respectively.The experimental results have verified the accuracy of the voltage rising transient analysis and the effectiveness of the gate driver proposed in this thesis.