Research On Active Gate Driver For Improving Gate Voltage Stability And Turn-Off Performance Of SiC MOSFET In Bridge Circuit

SiC MOSFET has been widely used in various types of power electronic converters because of the low switching loss,high operating frequency and high switching speed.However,in bridge circuit applications,the existence of circuit parasitic inductance,high switching frequency,and high speed of SiC MOSFET will aggravate the crosstalk phenomenon which affects the gate voltage(v GS)stability;and will cause transient drain voltage(v DS)spikes and oscillations in the turn-off process,resulting in avalanche breakdown in severe cases.These problems not only threaten the safe operation of semiconductor devices but also worsen the high-frequency electromagnetic interference(EMI)of power electronic converters.Therefore,based on the active gate driver,this thesis is committed to solving the problems of crosstalk and drain voltage spikes and oscillations of SiC MOSFET,which will improve the gate voltage stability and turn-off performance of the device.Firstly,the basic structure and operating characteristics of SiC MOSFET are analyzed,and the nonlinearity of the CGD is considered.By establishing the double pulse circuit model of SiC MOSFET with bridge circuit structure,the turn-on and turn-off process is analyzed in detail.The circuit models of upper and lower SiC MOSFET in the bridge circuit are established respectively.Then the formation mechanism and influencing factors of crosstalk issues,drain voltage spikes and oscillations are analyzed.Based on PSPICE software,the key parameters of the gate driver are simulated and analyzed to explore the influence on the switching characteristics.And the corresponding gate drive design reference is provided at the end of the chapter.Secondly,aiming at the crosstalk problem,a three-level active gate driver(TL-AGD)based on gate v GS detection and a gate voltage-clamped active gate driver(GVC-AGD)based on v DS change rate dv/dt detection are proposed respectively.The TL-AGD introduces a low-power p-channel MOSFET nearby between the gate and source,uses the original v GS to generate the control signal,and control the MOSFET to turn on to construct a three-level driving circuit;The GVC-AGD introduces a low-power n-channel MOSFET between the gate and source,detects the dv/dt of v DS and the change of v GS to control the conduction of MOSFET channel and body diode to form a low impedance circuit.Both of the above gate drivers have the characteristics of simple structure and control,no increase in switching loss,and no need for additional control signals.And detailed working principle analysis and parameter design are carried out,and the effectiveness of improving gate voltage stability is verified by simulation and experiment.Finally,aiming at the problem of drain voltage spikes and oscillations of SiC MOSFET,on the premise that the GVC-AGD can effectively suppress the crosstalk,and based on the original circuit structure,a gate voltage local raising circuit based on dv/dt detection is further proposed.By considering the nonlinearity of CGD,detecting the sudden change of dv/dt of v DS during the turn-off process,and reasonably designing relevant parameters,the circuit can effectively suppress voltage spikes and oscillations and meet the demand of dynamic change of load current.Finally,the experimental results show that the proposed gate driver can effectively suppress the electromagnetic interference of the system under the condition of effectively suppressing the drain voltage spikes and oscillations.74 figures,22 tables,99 references.