Research On Characteristics Of SiC Power Devices In Parallel And Gate Driver For Series Connection

With the commercialization of the third generation of power electronic power devices,Silicon Carbide(SiC)which is representative of the wide-bandgap semiconductors,is advancing the power electronics technology with its superior performance.Due to the limit of production process for manufacture SiC,the seriesparallel connection of the devices becomes a cost-effective way to expand the voltage and power levels.However,the influence of parasitic parameters on the current sharing and voltage equalization behavior of the SiC devices in the series-parallel connection,is an urgent problem to be solved.In this paper,under the background of series-parallel connection to promote power level,the parallel current sharing characteristics of parallel connection and drive circuit for SiC MOSFETs in series are studied.Firstly,the existing methods for the current parallel current sharing are discussed.In order to study the current sharing characteristics of SiC devices in parallel,the equivalent model of SiC MOSFETs with parasitic parameters is established,and then the specific processes of devices turned-on and turned-off are analyzed.Mathematical models of gate-source voltage and drain-source current of SiC MOSFETs are given.With the mathematical models,the critical condition between the dynamic and static current sharing behavior of SiC MOSFETs in parallel is given.The influence of parasitic parameters difference on the dynamic and static current sharing behavior is analyzed.Based on the experimental platform of SiC MOSFETs,the above parameters that have influence on the current mismatch are validated,and the main parameters influenced on the current sharing process are listed,which provide an effective basis for the parallel scheme design.Secondly,the coupling relationship between the power loss,temperature and parallel current mismatch is studied,as the on-resistance of SiC MOSFET has positive temperature characteristic.Combined with the parametric model and the equivalent circuits of the SiC MOSFET turned on and turned-off,the expressions of the power loss of SiC MOSFET are deduced.Furthermore,by the relationship between power loss and temperature,the influence of the increasing junction temperature casued by the power loss of device on the current mismatch is studied through the discretization analyzation method.Then correctness of the theoretical analysis is verified in the PLECS software.Finally,in order to solve the problem that when the SiC MOSFETs in series are driven by one single power supply,the traditional active clamp drivers will cause the delay of the driving voltage and the uneven dynamic voltage,a driver for SiC MOSFETs in series based on the isolated multi-winding transformer is proposed.Then,the working principle,modes and related device design scheme are analyzed,and the simulation model is built to verify its principle.The proposed driving structure not only effectively keeps the effective electrical isolation between the control side and the power side,but also realizes the driving voltage synchronization and the dynamic voltage sharing of SiC MOSFETs in series.