Modeling And Simulation Of Electromagnetic Interference In Converter Valve Of Flexible DC Transmission

With the development of smart grid,flexible DC transmission technology has gradually become the focus of power grid system.Modular multilevel converter（MMC）,as the core equipment of flexible DC converter valve,has attracted more and more attention.In order to promote the development of flexible DC transmission technology,scholars at home and abroad pay more attention to MMC.As the core device of flexible DC converter valve sub module,high-power IGBT will produce a large overshoot of voltage and current at the moment of IGBT on and off due to the influence of parasitic parameters,which will not only affect the normal operation of flexible DC transmission converter valve sub module,but also increase the generation of electromagnetic interference（EMI）.Therefore,electromagnetic interference has also become one of the main factors restricting the development of MMC,thesis will study from the following aspects:Firstly,the switching characteristics of high-power IGBT and the generation mechanism of electromagnetic interference in sub modules are studied.Through the research on the switching process of high-power IGBT device of flexible DC converter valve sub module,the relationship between various state variables of IGBT under the condition of test circuit is obtained.On this basis,it is analyzed,which is divided into transient model and steady-state model in the process of on and off.On this basis,the electromagnetic interference generation mechanism of flexible direct converter valve sub module and system level is discussed.Secondly,the equivalent circuit model of flexible direct converter valve sub module is established.The circuit modeling and simulation research are carried out for the flexible direct converter valve sub module structure.The simulation model built by ANSYS software can well simulate the operating conditions of the flexible direct converter valve sub module.The simulation waveform is compared with the experimental waveform to verify the correctness of the model.Thirdly,the radiated electromagnetic interference characteristics of flexible direct converter valve sub module are studied.Firstly,on the basis of fully considering the parasitic parameters of the sub module,this thesis analyzes the near-field and far-field radiation of the sub module,and finds that the main influencing factor comes from the common mode current of the sub module system.The common mode loop is analyzed by using the Davinan Norton equivalent principle,and the expression of common mode current is obtained to infer the radiated magnetic field of the sub module system.On this basis,the simulation and experimental platform are built,and the effectiveness of the model is verified by comparing the simulation results with the experimental results.Fourthly,a suppression method is proposed for the electromagnetic interference in the flexible direct converter valve system.In this thesis,the corresponding suppression methods are proposed from three aspects: drive optimization,electromagnetic shielding and RC filtering.Based on the equivalent model of flexible direct converter valve sub module structure,the action mechanism of suppression method is analyzed and verified by simulation.