Research On Parallel Current Sharing And Junction Temperature Estimation Of SiC MOSFET Based On Drain-source Current

The continuous development of power electronics industry promotes the rapid progress of power electronics technology.Power device has become an indispensable part of aerospace,renewable energy,electric vehicles and other fields.Compared with the traditional Si-based power devices,Silicon Carbide Based Metal-OxideSemiconductor Field-Effect Transistor(Si C MOSFET)has the advantages of low switching loss and high switching frequency,and has been widely concerned in the power electronics industry.However,with the complexity of the working states,the reliability of devices is increasingly required.It is particularly important to monitor the working state(such as junction temperature)and the electrical parameters(such as drain-source current)in real time.In some high-current the working states,due to the limited rated current of a single Si C MOSFET can not meet the requirements,so it is necessary to put Si C MOSFET in parallel to increase the current capacity,and the existence of unbalanced current in paralleled devices is a problem.At the same time,due to the high switching rate and low threshold voltage of Si C MOSFE,the problem of the shoot-through current is very easy to occur,which will accelerate the aging of the device and have a negitive influence on its reliability.This paper takes the drain current of Si C MOSFET as the starting point,and analyses the paralleled Si C MOSFETs current sharing method and the junction temperature estimation method when the shoot-through current occurs through theoretical and experiments.The main contents are as follows:(1)The physical structure of Si C MOSFET is introduced and its working principle is analyzed.Then,based on the actual paralleled circuit,the dynamic and static equivalent circuit models of paralleled Si C MOSFETs are established.Finally,the formation mechanism of the shoot-through current is analyzed.(2)A dynamic current sharing method considering the influence of temperature is proposed.Taking paralleled Si C MOSFETs as the research object,the mathematical model of dynamic unbalanced current is established,and the factors affecting dynamic unbalanced current are analyzed,and different measurements are taken for different factors.The factors that affect dynamic unbalanced current are mismatched threshold voltage and inconsistent source inductance.To deal with the unbalanced current caused by the mismatched threshold voltage,the inductance is connected to each branch at the same time,and a detailed theoretical derivation is given.While dealing with the unbalanced current caused by inconsistent source inductance and drain inductance,the inductance difference value is supplemented.The experimental platform is built,the data obtained from the experimental results are fitted,and the theoretical guidance formula needed for dynamic current sharing(that is to balance dynamic unbalanced current)process is finally obtained,so as to achieve the purpose of dynamic current sharing.(3)A static current method for paralleled Si C MOSFETs is proposed.Similar to the dynamic current sharing process,taking paralleled Si C MOSFETs as the research object,the mathematical model of static unbalanced current is established,and the factors affecting static unbalanced current are analyzed: inconsistent drain and source inductance.The inconsistent source inductance is the common cause of dynamic and static unbalanced current,so the inconsistent source inductance has been eliminated during the dynamic current sharing process,and the inductance difference value is supplemented to balance the drain inductance.The experimental platform is built,the data obtained from the experimental results are fitted,and the theoretical guidance formula needed for static current sharing(that is to balance static unbalanced current)process is finally obtained,so as to achieve the purpose of static current sharing.(4)A method for estimating junction temperature of Si C MOSFET based on the shoot-through current is proposed.Taking the half-bridge circuit as the research object,a junction temperature estimation method for Si C MOSFET based on the shoot-through current is proposed.The equivalent circuit for generating the shoot-through current is established and simplified,and the mathematical expressions of the crosstalk voltage and the shoot-through current are derived.The temperature dependence of the shoot-through current is analyzed,that is,the current is positively correlated with temperature.An experimental platform is set up to obtain the shoot-through current.The wave forms of the shoot-through current under different temperatures are obtained to verify the correctness of the theory.According to the experimental data,the relationship between the shoot-through current and temperature is fitted as the junction temperature estimation formula of Si C MOSFET.