Research On Driver Technology Of SiC MOSFET In EV Inverter

The development of electric vehicles has put forward higher requirements for miniaturization,lightweight and high energy efficiency of motor controllers.The wide bandgap devices as SiC MOSFET break through the performance caps of the traditional silicon-based power devices in voltage,switching frequency and temperature,which have obvious advantages in the application of electric vehicles.The weight,volume and cost of motor controllers may be significantly reduced and system efficiency can be improved.Driving circuit affects the performance and reliability of motor controllers.The research of driving technology is of great significance to the application of SiC MOSFET in EVs.In this thesis,the device characteristics of SiC MOSFET are analyzed,and the mechanism of main circuit oscillation and driving circuit oscillation of SiC MOSFET in high frequency applications are studied.For the CREE 1200V/300 A half-bridge module,LTSPICE simulation circuit with parasitic parameters is built,and the influence of driving circuit parameters on the switching process of SiC MOSFET is studied through theoretical analysis and simulation.According to the requirements of driving circuit of electric vehicle inverters,the driving circuit of 60 kW SiC inverters is designed,which has the functions of signal isolation,power buffer,active clamping,gate clamping and two-stage overcurrent protection.In order to reduce parasitic inductance of driving circuit,the layout scheme of low impedance path is proposed.The driving board is made and the experimental prototype is built.The switching performance of SiC MOSFET is tested by double pulse experiment,and the optimal driving resistance and gate capacitance are selected.In addition,the over-current protection circuit can operate normally in test,and the over-current point is close to the design value.The power test and bridge arm crosstalk test of the inverter are carried out through the motor bench test.The results show that the crosstalk voltage is within the safe range.The driving circuit designed in this thesis can effectively guarantee the safe and reliable operation of the inverter.The traditional driving circuit uses fixed driving parameters,which can not exert the advantages of SiC MOSFET.In this thesis,a new active driving circuit is proposed,which controls the rise and fall time of current through di/dt detection circuit and shunt circuit.It can reduce the delay and loss of switch under the same electrical stress conditions.In addition,the junction temperature control strategy based on active gate driver is studied,and the loss model of SiC MOSFET is established.By changing the driving voltage and resistance,the conduction loss and switch loss are controlled to reduce the junction temperature fluctuation caused by load changes.LTSPICE model is used for simulation analysis.The results show that the junction temperature fluctuation of SiC MOSFET can be significantly reduced by using junction temperature smoothing control,and the power cycles of the inverters can be increased.