Research On Characteristics And Driver Protection Of High Power SiC MOSFET Devices

Silicon Carbide(SiC)devices have distinct advantages in high-voltage and high-power applications due to its high breakdown voltage,fast switching speed,increased operating temeperature,higher thermal conductivity,and lower on-state resistance.However,undesired overshoot and oscillations of voltage and current occurred in converters with SiC devices during switching transients decrease reliable application of SiC devices.The characteristics and driver protection technology of SiC MOSFET is focused in this thesis.Firstly,the static characteristics of SiC devices,and the trend of saturation voltage drop,threshold voltage,and on-state resistance vs.temperature are studied.Switching characteristics are tested using double pulse test(DPT),and the impacts of parasitic inductances on the switching performance of SiC devices is analyzed.Then a layout method based on vertical structure and magnetic field cancellation is proposed to reduce the loop parasitic inductance and to suppress the turn-off overvoltage.SC experiments of SiC MOSFET in hard switching fault(HSF)are developed to analyze the SC mechanism and withstand capability.Moreover,main reasons that desaturation(DeSat)sensing method for SiC is not effective are presented.PCB Rogowski coil is used to sense current through the device reliazing SC protection for SiC MOSFET.Operating principle and working states in differential and self-integration of Rogowski coil are introduced as well.Design method of PCB Rogowski coil and the anti-interference performance of returning turn are presented.Parameters of PCB Rogowski coil are designed.Analysis of impedance characteristics and frequency characteristics are offered.The experimental test for PCB Rogowski coil is implemented under SC fault,and the experimental result show that the current sensor satisfies the requirement of SC protection.Finally,driver protection hardware is designed,including power supply,fiber isolation,power amplifier circuit,soft turn-off,and signal processing circuit of Rogowski coil.The driver is validated by experiments.Performance of the driver satisfies high frequency requirement of SiC MOSFET.Then,the controllable method of SiC MOSFET by altering gate resistance,auxiliary gate-source capacitance,as well as positive-and negative-bias gate voltage are investigated.The SC experimental results under various faults validate that the SC protection method based on PCB Rogowski coil can achieve reliable protection for SiC MOSFET.