Research On Parallel Active Current Sharing Of Silicon Carbide MOSFETs

With the improvement of industrialization level,the traditional power electronic devices are difficult to meet the increasing requirements due to their own material factors.The wide bandgap materials such as silicon carbide and silicon carbide(SiC)MOSFET have attracted the attention of researchers.In the production and application of silicon carbide MOSFET,due to the limitations of silicon carbide wafer size,slow growth rate,insufficient production capacity and high price,the development and application of silicon carbide MOSFET on a larger scale are restricted.The parallel application of low current level SiC MOSFETs can alleviate the problems of insufficient capacity and high cost of high current level chips,and effectively improve the system power density.Therefore,it is urgent to solve the problem of unbalanced current in parallel operation.The factors that may lead to current imbalance are analyzed one by one,and combined with the simulation results,a current sharing method based on active control of core inductor combined with grid drive circuit is proposed to suppress the occurrence of current imbalance.The main contents of this paper are as follows:1.The factors affecting the characteristics of the FET and the switching process are studied.Taking the commercial SiC MOSFET produced by Cree company as the research object,combined with the basic parameters provided in the data book,the dynamic and static characteristics including device selection,output characteristics and transfer characteristics are analyzed,as well as the analysis and verification of the switching process and the influencing factors of the switching process.At the same time,the PSPICE software of cadence is used to simulate the influence of parasitic parameters on the switching process based on the spice model provided by its official website.The simulation results are verified by physical experiments,which provides technical guidance for the use and selection of SiC MOSFET.2.Based on the double pulse test circuit,the new branch is paralleled to form a parallel test circuit.The factors that may lead to current imbalance are analyzed one by one.The analysis factors include the difference of parasitic parameters of SiC MOSFET in parallel operation,the size of driving voltage,driving resistance and other factors that may affect the current imbalance in the power circuit.Through the analysis of the influence of different factors on the current imbalance,the necessity of taking current equalization measures is proved.3.Aiming at the current imbalance phenomenon,a method of active current equalization is proposed by combining core inductor with grid drive circuit.The working principle of the core inductor is analyzed and the appropriate core material is selected.In the scenario of multi chip parallel use,the relevant formula is summarized.The current sharing mode of the core inductor reduces the current unbalance by more than 5%.At the same time,the active control method of grid drive circuit is proposed,which can reduce the current imbalance by 2%-4.2%.Finally,the feasibility of the two current equalization methods is proved by experimental verification.