Research On Electromagnetic Disturbance Characteristics Of IGBT Switching Transient Process And Suppression Measures

With the rapid development of flexible DC power grid,IGBT devices are developing in the direction of high frequency and large capacity,and their faster switching speed and higher switching frequency also introduce more complex electromagnetic disturbance(EMD)problems to power system.The switching voltage and current of IGBT are the main disturbance sources for power electronic devices such as converter valves.The EMD caused by the IGBT switching action have a significant impact on the stable operation of power equipment.In this paper,the EMD characteristics of IGBT and its suppression measures are deeply studied by combining modeling analysis and experimental measurements.Firstly,the influence of switching transient characteristics of IGBT in different stages on EMD characteristics is studied,and the disturbance source model of IGBT is established.In this model,the change rate of transient current and voltage is calculated in stages.and the effects of nonlinear capacitance and parasitic parameters on di/dt and du/dt are considered,as well as the turn-on oscillation process caused by parasitic capacitance and inductance.It is verified that the current model proposed in this paper can predict the EMD peak induced by turn-on current oscillation.The trailing current has little effect on the characteristics of current disturbance source.so the trailing current process can be ignored in the current model.The influence mechanism of gate-collector capacitance Cgc on the characteristics of voltage disturbance source is revealed,and then the modeling method of multi-stage capacitance is proposed to improve the accuracy of voltage model for voltage spectrum prediction.Through the comparison between experiment and models,it is suggested to adopt three-stage Cgc equivalent model to achieve a balance between complexity and accuracy of voltage model.The total power contained in the switching waveform spectrum is proposed as a numerical index,which is used to quantify the high-frequency component of the disturbance source.and then the numercial relationship between the parasitic parameters and the EMD level is analyzed.Based on the disturbance source model of IGBT,this index is used to quantitatively evaluate the influence of device parameters and switching circuit parameters on the voltage and current disturbance sources,and the relevant conclusions can be used to guide the key parameters regulation.The test platform for IGBT switching characteristics is established,and the time-frequency distribution of IGBT disturbance sources under different parameters is obtained,and the anlysis results of the model are verified.Then,the EMD test platform based on buck circuit is established,and the EMD characteristics of power devices are studied experimentally from switching characteristics,conducted disturbance and radiated disturbance.The influence law of driving circuit on conducted disturbance of IGBT converter is revealed.In order to fully dem ostrate the EMD characteristics of IGBT,the disturbance sources and EMD measurement results of Si IGBT and SiC MOSFET is compared.The experimental results show that the common mode(CM)and differential mode(DM)interference of the converter based on SiC MOSFET is higher than that of Si IGBT in 8-30MHz,and the difference of DM interference is more significant.In addition,the severe turn-on current oscillation process of SiC MOSFET leads to obvious peaks of conducted and radiated disturbances at the turn-on oscillation frequency,which is the weak point of electromagnetic compatibility of SiC MOSFET in practical applications.Therefore,the turn-on oscillation current model of SiC MOSFET module is proposed,which can reflect the accurate value of drain-source capacitance at different stages of turn-on process.Compared with the traditional second-order model,the accuracy of the proposed turn-on oscillation current model is significantly improved.Finally,the suppression measures for conducted disturbance of IGBT gate driver are studied.Filter is the most commonly used EMD suppression measure,but the filtering performance is easily affected by coupling parameters and greatly reduced.In this paper,the influence mechanism of various mutual inductances on filtering performance is revealed,in which the mutual inductance between capacitors is the key factor leading to the decline of filtering performance.Through the design of BNC port,the independent and accurate extration of various mutual inductances is realized.The influence of mutual inductance on filtering performance is evaluated quantitatively,and a simplified filter model is established based on the evaluation results.Then,a new mutual inductance elimination method is proposed.This method makes the coupling effect of input and output traces will add a negative inductance to the transfer branch of the filter,which is used to cancel the mutual inductance betwwen capacitors.Then the total mutual inductance between the input and output loops of the filter can be completely eliminated.Through modeling analysis and experiments,it is verified that the mutual inductance elimination method proposed in this paper can completely eliminate the mutual inductance without adding additional components,and significantly improve the high frequency performance of the filter.