Research On Active Current Sharing Methord For Parallel High Power SiC MOSFET

In recent years,the third generation of wide bandgap semiconductor devices represented by silicon carbide(SiC)has become a research hotspot.Among them,SiC MOSFETs are expected to replace Si IGBTs in high-voltage,high-frequency,and high-temperature applications due to their excellent characteristics,meeting the needs of higher-density applications.Based on the design of SiC MOSFET driver circuit,a new method for parallel active current sharing on high power SiC MOSFET was proposed in this paper.Firstly,the device structure and switching characteristics of SiC MOSFETs are introduced.In order to optimize the switching waveform of SiC MOSFET,the switching process is divided into different stages to control,and a variable gate voltage gate drive structure is proposed.This method can change the current and voltage slope during the switching process without affecting the switching time,thereby the current and voltage spikes can be reduced at the same time.For experimental analysis and parallel application,the parallel structure of the device was designed and simulated by SolidWorks and ANSYS Q3D software to obtain a symmetrical parallel structure.Also,this paper systematically analyzes the factors affecting the current distribution of SiC MOSFETs in parallel applications from three levels:device,drive loop and power loop.Finally,based on the variable gate voltage gate drive structure,an active current sharing method basedr on di/dt current detection fo gate voltage delay compensation and switch voltage compensation is proposed.The former makes the parallel current change edge synchronous.The latter is u4sed to adjust the slope and peak of the current change.The working process is described and the simulation analysis of the current sharing control is carried out,witch means the method is feasible.A double-pulse and short-circuit test experimental platform is built.The experimental results show that the gate drive structure of this paper can effectively optimize the switching waveform and safely turn-off the device under short circuit conditions.Also,the parallel experimental platform is built.And the effects of different parameters on the parallel current balance of SiC MOSFET and the current sharing under different operating conditions are analyzed through experiments.Finally,the active current sharing method is used to improve the parallel non-uniform flow of SiC MOSFET.In the turn-on process,the difference in current spike before improvement is 60A,and the current peak gap is reduced to 40A after delay compensation.After switch voltage compensation,the parallel current is almost the same.During the turn-off process,The difference in current before improvement is achieved 40A,and the waveform after the delay compensation is almost coincident,which proves that the active current sharing method can improve the parallel current unevenness.