| Three-level converter,which uses IGBT as power switching devices,are widely applied in high-power variable-frequency speed control systems because of its advantages such as low switching losses,high efficiency,and low output harmonic content.However,with the increase of the power and switching frequency of the equipment,the problems of electromagnetic interference(EMI)caused by the fast action of switching devices is become more and more prominent.This will not only affect the converter's stabilization but also may affect the normal operation of its surrounding equipment,so it is urgent to study and suppress it.This paper studied the electromagnetic interference(EMI)suppression technology of three-level converter in high-power variable-frequency speed control system.Firstly,the parasitic parameters of the IGBT and its gate drive circuit are analyzed,and the dynamic model of the IGBT is established based on Simplorer and its effectiveness is verified.In view of the mechanism of the driving circuit's effect on the device switching characteristics,the switching process of IGBT is analyzed in detail,and the influence of different gate resistance and gate-emitter external capacitance on the dynamic characteristics of IGBT is analyzed through simulation,which provides support for the optimal design with electromagnetic compatibility of the gate drive circuit.The EMI of gate drive circuit caused by the driving voltage overshoot is analyzed and one suppression method is proposed,and the effectiveness of the method is verified by simulation and experiment.Secondly,the interference source of the system is analyzed from the aspect of physical model,and its propagation path is given,and the limit standards and test results of the conducted EMI of the converter are introduced.With the phenomenon of interference value exceeding the standard in the results,one method to suppress conducted common-mode EMI is proposed from the aspect of transmission path in the product design stage,which based on increasing the common-mode impedance of power devices to earth and blocking or changing the interference circulation path.By using MATLAB and CST,the paper simulated the interference characteristic of system and the surface electric field of heat sink with and without the suppression method separately,and the results show that the method can effectively suppress the conducted common-mode EMI emission of the converter.Then,it is proposed that the EMI filter is the most effective way to suppress interference from the EMI characteristic path in the product modification stage.The paper expounded the theory of EMI filter and analyzed the factors that affect its insertion loss value in detail.Aiming at the situation where the system conducted EMI partially exceeded the standard,the single-stage filter,the two-stage filter and the EMI filter with matching network were designed and gradually optimized,and the effectiveness of the designed EMI filter was verified through Multisim simulation and experiment,so that the value of conducted EMI of the system met the national standard.Finally,the interference source of the three-level converter radiated EMI is analyzed and its interference propagation path is given.The limit standards and test results of the radiated EMI of the converter are introduced,and the interference exceeding the standard in the results was suppressed based on the cable shielding technology.The distribution of electromagnetic fields around the cable is analyzed by CST electromagnetic field simulation.Using field circuit co-simulation in CST,the factors that affect its interference suppression effect are studied from several aspects such as the grounding method,specific structure,termination method and ground loop of the shielding layer.Applying the conclusions to the system modification,the value of radiated EMI of the three-level converter met the national standard.There are 105 figures,10 tables and 74 references in this thesis. |
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