Research On Driving Techniques Of SiC MOSFET In High-Speed Switching Application

Due to the narrow band gap of silicon material,Si-based power device has reached the limit of silicon material in terms of blocking voltage,energy consumption,operating temperature and switching frequency,which makes it difficult to meet the requirements of the new generation of power system and become the bottleneck of the development of power electronic system.Silicon carbide(Si C),as the third generation of wide band gap semiconductor material,is the most promising alternative to silicon(Si),which can be chosen to make the new generation of power semiconductor devices.The band gap width of SiC is three times that of Si,the breakdown field strength of SiC can reach 10 times that of Si,the thermal conductivity of SiC is 3.3 times that of the Si,and the saturation electron drift rate of SiC is 2.5 times that of Si.Therefore,Si C-based MOSFETs have already entered the industrial market with the advantages of high blocking voltage,fast switching speed,small conduction loss and high temperature endurance.The research of SiC MOSFET devices is relatively mature and power electronics applications based on SiC MOSFET device are also developing rapidly.However,the research of SiC MOSFET driving and protection circuit is still in its infancy.Since the SiC MOSFET driver and protection module directly controls the switching of the SiC power devices and directly affects the performance and efficiency of the power devices.Therefore,the research and improvement of the driving and protection circuit of SiC MOSFET makes SiC power devices more reliable in the power electronic system,which is of great significance for the promotion of SiC power devices.Based on the studied research on the driving and protection of SiC MOSFETs,optimization has been conducted for the design of ultra-high speed applications of SiC MOSFET(100k Hz-1MHz)in this paper.Improvements have also been made for DESAT detection and overcurrent protection under high-speed switching frequency.The fault status can be latched and counted for both overcurrent protection and over-voltage and under-voltage protection of gate,which can improve anti-jamming capability of fault detection under high switching frequency.In addition,a dynamic current-sharing structure is proposed for the driver of high-speed SiC MOSFET parallel applications,which can adjust the shunt of the parallel devices in the switching transients to improve the reliability of the SiC MOSFET devices in parallel applications.The main contents of the study are as follows.(1)In chapter 1,the development status and application prospect of silicon carbide material and devices are analyzed,and the research status of SiC MOSFET driving protection is reviewed.(2)In chapter 2,the switching dynamic characteristics and current sharing characteristics of parallel SiC MOSFET devices are analyzed.The key factors influencing the driving of SiC MOSFET high-speed applications and parallel applications are obtained through theoretical research and simulation.(3)In chapter 3,based on the theoretical research,the power supply selection(driving voltage,peak current,etc.),isolation mode selection,driving structure design,control and protection circuit design,test circuit selection and other aspects are fully considered and analyzed before the determination of the reasonable and feasible SiC MOSFET high-speed drive protection module.Simulation of the module has been done in the Cadence PSpice platform,the simulation results shows that the driving module can stably work in above 500 k Hz with over-current protection,over-voltage and under-voltage protection,dynamic current sharing,error state latching and other important functions.(4)In Chapter 4,Based on simulation results on Cadence PSpice,the PCB schematic and layout of the SiC MOSFET driving and protection module are drawn under Altium Designer and test of the prototype is made to verify the above design.The experiments show that the module could operate at 1MHz at power rating of 200 W and 500 k Hz at power rating of 1.25 k W.Besides,the design function of overcurrent protection,over voltage and under voltage protection,dynamic current balancing is consistent with simulation results.Furthermore,the difference of gate driving resistance and gate voltage threshold between parallel devices will cause dynamic current imbalance and the caused temperature difference cannot be balanced by the positive temperature coefficient of on-resistance of device which proves the importance of the dynamic current balance structure for SiC MOSFET parallel applications.