| The performance of power converters is closely related to switching devices.The development of traditional silicon-based switching devices has approached the physical limit of silicon materials,which is the main factor limiting the improvement of power converter performance.The emergence of the third generation of power switching devices represented by SiC MOSFETs provides a new opportunity for the development of power converter.Compared with Si MOSFETs and Si IGBTs,SiC MOSFETs switch faster and the contradiction between switching losses and device stress is more serious.Increasing the gate resistor value is a conventional method to reduce switching stress but it increases switching losses and switching time.For this reason,the current operating frequency of SiC MOSFET power converter is far less than its theoretical value,which greatly limits the application range of SiC MOSFETs.Therefore,studying the characteristics of SiC MOSFETs to design a driving circuit that can reduce switching losses without increasing switching stress is of great significance for maximizing the potential of SiC MOSFETs and improving the performance of high-power converters.This thesis firstly conducts theoretical research and simulation analysis on the switching characteristics of SiC MOSFET,and summarizes the optimization method of switching loss from the driving level: controlling the driving voltage,resistance or current in stages.Secondly,according to the characteristics of the voltage-type drive,a two-stage resistance switching type drive circuit is designed,and the drive resistance is controlled in stages by using a delay circuit and a MOS switch.According to the characteristics of current-type driving,a feedback control-type driving circuit is designed.The stage of SiC MOSFET is judged by detecting the rate of change of the drain-source voltage and current during the SiC MOSFET switching process,and the feedback circuit is used to inject or draw current into the gate at a specific stage to achieve the staged control of the drive current.Finally,the two driving circuits were simulated and verified by building a double-pulse test simulation platform in LTspice XVII software.Simulation results show:(1)The two driving circuits can optimize the contradiction between switching loss and device stress.Compared with the traditional drive circuit,when the control current overshoot is 8A and the voltage overshoot is 50 V,the two-stage resistance switching type drive circuit reduced turn-on losses by 17% and turn-off losses by59.7%,and the feedback control type driving circuit is reduced by 55.3% and 55.4%,respectively.(2)The two driving circuits have good adaptability to the working conditions.When the load current is 40 A,50A,and 60 A,respectively,they always have excellent control performance for the SiC MOSFET switching process. |
