Research On Silicon Carbide MOSFET Modeling And Switching Ringing Suppression Method

The third-generation wide bandgap semiconductor devices represented by silicon carbide(SiC)MOSFETs have been widely used in fields such as switching power supplies,electric vehicles,and smart grids.Due to the high-speed switching capability,low-conduction voltage drop,and excellent high-temperature characteristic of SiC MOSFET,it becomes an important device to replace Si IGBT.However,the switching ringing caused by the high-speed switching and low damping characteristics of SiC MOSFETs seriously affects its high-reliability applications.The switching ringing would wrongly trigger the device and damage itself,increase power losses,and introduce a large amount of electromagnetic interference(EMI)noise.Therefore,to take full advantages of SiC MOSFET,the switching performance must be studied in detail.For this purpose,this article establishes a SiC MOSFET SPICE model that considers temperature effects to accurately predict and describe the switching waveforms of SiC MOSFET during the design stage of power converters.Additionally,this paper proposes equivalent circuit models of the turn-on and turn-off for SiC MOSFET and guides the design of the DC-side RC snubber circuit.In view of the main content of this article,the existing research still has the following deficiencies:The construction of SiC MOSFET behavior model:There are certain differences between waveforms obtained from SiC MOSFET model and experimental results.Therefore,the actual waveforms cannot be fully predicted.The exsiting modeling work is mainly based on the datasheets provided by the manufacturer.However,the characteristic curves in the datasheets are mostly typical values and the information contained is not enough to model a specific switching device.Besides,when the coaxial shunt is used to measure current,the influence of the parasitic parameters of the current measurement loop on the observed waveforms is not considered,which will affect the fitting parameters for the SiC MOSFET model and the accuracy of the model.Design of the DC-side RC snubber circuit:for the equivalent circuit model of the turn-on and turn-off for SiC MOSFET,most studies usually assume that the excitation source of switching ringing is located on the DC-link.However,for actual voltage source converters,the DC-link voltage is usually regarded as a constant.According to the linear control theory,the position of the excitation source has a great influence on the derivation of the transfer function.Therefore,the method will lead to inaccurate calculation of the transfer function and cause errors in the description of the switching ringing.Due to the complex caculation for the fourth-order system,the current design methods of RC snubber circuit generally rely on simplified third-order circuit models.The reduction of the system order is convenient for analysis and calculation,but this simplification will impair the accuracy of the RC snubber parameters.For the above problems,this article first measures the static characteristic curve of the SiC MOSFET by power device analyzer.The terminal capacitance measurement circuit for SiC MOSFET is established and the C-V curve is measured by impedance analyzer to avoid the deviation between the reality and the characteristic curve provided by the manufacturer.Based on the measurement parameters,the modeling methods of parasitic gate-drain capacitance(C_gd)and drain-source capacitance(C_ds)are improved and SiC MOSFET SPICE model considering temperature effects is established.The parasitic parameters of the current measurement loop for the coaxial shunt are modelled.Simultaneously,a simulation model for SiC freewheeling diode is achieved to effectively verify the performance of the SiC MOSFET model.Then,considering high-frequency electromagnetic interference is actually caused by the fast switching of the power device,the excitation source is placed inside the SiC MOSFET itself and simplified equivalent circuit models both the turn-on and turn-off for SiC MOSFET are proposed.Based on the proposed models,the DC-side RC snubber circuit is added to suppress the switching ringing of the device.Since the ringing is essentially caused by the imaginary part of the poles,this paper proposes an optimized design method by the way actively configuring poles.The exhaustive method is used to determine the RC snubber region that can completely suppress the ringing.This method can derive the snubber region where both the turn-on and turn-off ringing can be suppressed simultaneously.That effectively solves the problem of calculating the fourth-order system.Finally,SiC MOSFET(C2M0080120D,Cree)is taken as an example and a double-pulse test platform is designed and built.The simulation circuit is constructed in software LTspice,and experimental results under the same conditions are compared and analyzed.The results show that the improved SiC MOSFET SPICE model considering the influence of temperature can better predict and describe the experimental waveforms.In addition,the modeling of parasitic parameters in the current measurement loop for coaxial shunt increases the accuracy of the model.The improved simplified equivalent circuit model of both turn-on and turn-off for SiC MOSFET can accurately explain the ringing phenomenon and provide theoretical guidance for the design of the RC snubber circuit.The DC-side RC snubber circuit designed in this paper can eliminate completely the ringing phenomenon of the turn-on and turn-off.The optimization design method for RC snubber circuit can achieve more excellent suppression performance,and the suppression effect is better than the previous calculation method based on a simplified third-order system.