Research On Gate Drivers And Snubber Circuits Of Silicon-Carbide MOSFET

In recent years,with the rapid development of power electronics technology,traditional Silicon materials have been unable to meet the requirements of high efficiency,high power density and other special applications for the sake of the limitations of their physical characteristics.But SiC power devices have obvious advantages in achieving high frequency,miniaturization,and light weight of power electronic converters because of their fast switching speed,low loss,and high switching frequency.However,due to the influence of parasitic parameters,the high switching speed of SiC MOSFET has caused serious voltage overshoot and oscillation problems,and there are crosstalk problems in the application of bridge circuits,which affects the stability and safety of the device.This requires a gate driver and a snubber circuit with excellent performance in order to fully exert the excellent switching performance of the device,making SiC devices widely used in high-speed and high-frequency applications.Therefore,this paper has conducted in-depth research on the snubber technology and gate driver of SiC MOSFET.Based on the parasitic equivalent circuit model of SiC MOSFET,the dynamic switching characteristics during the commutation of one-phase bridge arm are analyzed.Considering the influence of circuit stray inductance and the non-linear changes of parasitic capacitance,the equivalent impedance formula in the switching process is deduced,and the principle of oscillation formation is clarified.At the same time,the principle of crosstalk is analyzed,and the peak values of positive and negative crosstalk voltages are derived respectively.Formula and analyze the factors that affect the peak value of crosstalk voltage.Finally,the dual-pulse test experimental platform is used to test the basic switching characteristics of the device as well as the oscillation and crosstalk issues.Passive snubber circuit is a simple and practical method to suppress the switching oscillation of SiC devices.For the three kinds of passive buffer circuits commonly used in Sibased devices: RC snubber,RCD snubber and clamp RCD snubber,the working principle of the three passive snubber circuits to suppress switching oscillation is analyzed.The three are compared and studied in terms of the aspects of the working voltage range of the snubber capacitor,switching characteristics,switching losses,and the difficulty of parameter design.Finally,combining with the high-speed and high-frequency characteristics of SiC devices,it is pointed out that the clamped RCD snubber circuit is more suitable for high-speed and highfrequency applications of SiC devices.In addition,The double-pulse experiment verifies the correctness of the analysis.At the same time,the effects of the changes of the snubber capacitance and snubber resistance on the switching characteristics and switching losses under different working conditions are experimentally studied,which provide a reference for the design of snubber parameters of SiC devices.A design method for gate driver resistance is proposed,which solves the problem of usually relying on a large number of experimental trial parameters.For a gate driver circuit with passive crosstalk suppression,considering the coupling relationship between crosstalk suppression capacitor and drive resistance,a parameter optimization design method of crosstalk suppression capacitor and gate driver resistance is proposed.Through the double-pulse test experiment,the feasibility and effectiveness of the parameter design method and the optimization of the designed parameters are verified.Aiming at the problem that the existing crosstalk suppression circuit absorbs the crosstalk voltage and sacrifices the switching speed,a new SiC MOSFET gate driver is proposed.The gate driver accelerates the switching on and off of the device by changing the driving resistance,and clamps the crosstalk voltage at a fixed voltage level,which solves the contradiction between the switching speed and crosstalk suppression,and gives the parameter design method.Through the LTspice simulation software,compared with similar gate drivers,the superior performance of new SiC MOSFET gate driver in switching speed and crosstalk suppression is highlighted,and the rationality of the parameter design method is verified.