The Research On The Proportional Adaptive Driver And Short Circuit Protection Of SiC BJT

Being the core of power electronics technology,power semiconductor devices,especially the silicon carbide devices in the third generation of wide band gap semiconductors are far superior to Si devices in physical properties such as critical breakdown electric field,band gap width,thermal conductivity,etc.Therefor it will become a hot research and application direction in the future,and has a good application prospect in high frequency,high efficiency,high power density equipment.With similar switching speed and specific on-resistance as the mainstream device MOSFET,SiC BJT has no gate oxide reliability problem of MOSFET;thus,it has unique application advantages in high temperature environment.The performance of the driving circuit,however,restricts the use of SiC BJT in two aspects.First,the structure is complex and the steady-state loss is too large,and a large amount of redundant power consumption is generated under light load,which is the main factor affecting its market acceptance.The second is that the current commercial drivers do not integrate the corresponding protection functions,which make the reliability of equipment applications lower.In this light,the theoretical analysis and experimental exploration were carried out in this thesis to provide a solution in order to improve the performance and practical value of BJT and the content is listed as follows:1.As a current-controlled device,SiC BJT requires a large constant driver current to maintain conduction which results in excessive power consumption and limits its market acceptance.In terms of reducing the steady-state driver loss,this thesis analyzes the traditional driver circuit and the proportional driver circuit and then an proportional adaptive driver applied to SiC BJT was designed,including the selection process of the main components and the analysis of the loss composition.The innovation of this thesis lies in its use of thermal matching and coupled Si BJT to realize the controllable current source controlled by collector current and temperature,so as to provide the base driving current of SiC BJT with the change of working conditions.This driver can minimize the steady-state power consumption of the base drive in a wide range of load current and operating temperature.2.According to the design principle of the proportional adaptive driver,the real circuit is made and the test platform is set up and the comparison between it and the dual source base driver in the boost converter is studied.The results show that the proportional adaptive driver can reduce the power consumption of the base driver by more than 50%,which verifies the feasibility of the new driver to provide the base current related to the collector current and temperature for the SiC BJT.In order to study whether the proportional adaptive drive can enhance the market competitiveness of SiC BJT,the mainstream device SiC MOSFET was selected as another comparison item to analyze the maximum power loss at different input voltages,load currents and operating temperatures.And the results represent that the overall losses of SiC BJT is slightly higher than that of SiC MOSFET due to its relatively higher level of turn-on and driver losses though its turn-off and conduction losses are smaller than that of SiC MOSFET.Finally,an experimental comparison is made between SiC BJT inverter based on dual-source driver and proportional adaptive driver and SiC MOSFET inverter,which further illustrates the characteristics of proportional adaptive driver in the reverse freewheeling process that hardly generates driving losses.The experimental results show that in the power range of 550W to 1500W,the loss of proportional adaptive driver is only 11.2%-28%of that of dual source drive and among the three inverters though the inverter using the proportional adaptive driver has the highest efficiency though the THD of the SiC MOSFET inverter is the smallest.3.In view of the lack of special BJT driver chip with protection function in the market,which leads to the problem of poor reliability in the application process of SiC BJT,this paper first analyzes the short circuit fault of power devices,and then designs a circuit which can effectively carry out short circuit protection based on the principle of V_CEdetection and desaturation protection.Finally,the simulation analysis and experiment are carried out.The results show that the circuit can turn off the device quickly and effectively in 600ns in case of short-circuit fault of SiC BJT,avoid local overheating caused by excessive power consumption,prevent false triggering after fault,and improve the reliability of the device and system.