Research On Electromagnetic Interference And Suppression Of Motor Drive System Based On Silicon Carbide MOSFET

With the requirement of motor drive system for power density,it is necessary to reduce the size of the drive module by increasing the switching frequency of the power semiconductor.Wide-bandwidth semiconductor devices,such as silicon carbide MOSFETs,have faster switching speed and will gradually replace traditional silicon semiconductor devices.Compared with traditional silicon MOSFETs,silicon carbide MOSFETs have higher dv / dt and di / dt.Oscillations occur on the switching time-domain waveform,which is the main cause of electromagnetic interference noise.Therefore,in this thesis,we will study the electromagnetic interference and its suppression methods in a SiC-based MOSFET motor drive system.The main content is divided into the following parts.Firstly,study the modeling method of the switching waveform.The source of electromagnetic interference is the pulse waveform generated by the silicon carbide MOSFET during the switching transient.Therefore,this thesis models the switching waveforms of silicon carbide devices to study electromagnetic interference.Analyzing the advantages and disadvantages of modeling methods of switching waveforms used by scholars nowadays,combined with the switching waveforms in actual circuits,this thesis proposes a more accurate modeling method of switching waveforms,and the influence of parameters in the model on the noise spectrum is analyzed.Secondly,this thesis studies the electromagnetic interference characteristics of silicon carbide MOSFETs based on the BUCK circuit and the synchronous BUCK circuit.First of all,based on the consideration of the parasitic parameters of the silicon carbide MOSFET,this thesis analyzes the switching process and simplifies the second-order RLC equivalent circuit after the MOSFET is fully turned on and completely turned off.According to the equivalent circuit,Kirchhoff’s voltage law is used to obtain the secondorder differential equation.After solving it,the time domain expression of the switching waveform of the silicon carbide MOSFET is obtained.The spectrum is obtained by Fourier transform,and the maximum value is obtained in different frequency ranges to obtain the spectral envelope.Then a BUCK circuit simulation and experiment platform is built.By comparing the time-domain waveform and frequency spectrum of the switching waveforms obtained from calculations,simulations,and experiments,it is shown that the analysis model proposed in this thesis can better predict the chang trend of electromagnetic interference in the synchronous buck circuits.Finally,based on the synchronous BUCK circuit,the control variable method is used to change different parasitic parameters one by one,and its influence on the electromagnetic interference characteristics of the device is studied.Thirdly,this thesis studies the method of suppressing electromagnetic interference of motor drive system.In this thesis,RC snubber circuits,ferrite beads,and decoupling capacitors are added to suppress electromagnetic interference.First,based on the equivalent model of the synchronous buck circuit,the mechanism of the suppression method is analyzed and verified by simulation.Then build a motor drive system experimental platform,add these suppression measures to the system,compare the magnitude of electromagnetic interference before and after the addition,and verify the effectiveness of the suppression measures.