Research On Modeling Of Radiated Electromagnetic Interference In Industrial High-Power Frequency Converters

With the increasing switching frequency of frequency converters widely used in the industrial field,the electromagnetic interference(EMI)of high-power industrial frequency converters is becoming increasingly serious.With the internationalization of products,radiated EMI has become a hot topic of attention in the industry.Radiated EMI is not only difficult to suppress,but also the source of interference is difficult to identify,radiation source are difficult to identify and the description of the interference mechanism is not clear enough.Therefore,it is necessary to model and study the radiated EMI of industrial high-power frequency converters.The internal circuitry and physical structure of the high-power frequency converters first are analyzed from an EMC perspective in this paper,and the typical radiation sources of the high-power frequency converters is analyzed,focused on the identification and analysis of radiation sources that emit radiated EMI in the form of antenna radiation within the high-power frequency converter.Radiation EMI sources with DC bus planes and the switching transistor drive back circuit as radiating antennas are identified.Then,the mechanism of radiated EMI generated by the typical structure of the DC bus plane of the frequency converter is analyzed,and a radiation EMI model of the DC bus plane of the frequency converter is established in this paper.This model includes a radiation excitation source model of the DC bus plane and a model of the input impedance of the unconscious radiation antenna of the DC bus plane,and the input impedance characteristic of the DC bus plane under different physical structures are also analyzed.A prediction model of the radiation electric field of the DC bus plane is established,which can describe the mechanism of radiation EMI generated by the DC bus plane of the frequency converter.Based on this model,the characteristics of radiated EMI generated by the DC bus plane are analyzed.Radiation EMI modeling on the switching transistor drive back circuit is analyzed in this paper.Firstly,the excitation source of the switching transistor drive back circuit is identified,and then the input impedance models of the switching transistor drive back circuit with linear and bent structures are established.Then,the input impedance characteristics of the switching transistor drive back circuit are analyzed.Finally,based on the excitation source and input impedance model,the radiation electric field prediction model is established.Based on the radiation EMI model,the radiation EMI characteristics of high power frequency converters are analyzed.In response to the problem of difficulty in obtaining the internal impedance of the radiation excitation source under the operating state of the frequency converter,an online impedance measurement technique for the internal impedance of the radiation excitation source is proposed in this paper.Firstly,the influence mechanism of the interference source on the measurement accuracy of the measurement system is analyzed,and then a measurement technique which can eliminate the influence of the interference source on the measurement accuracy of the measurement system is proposed.Finally,an experimental platform is established to verify the effectiveness of the proposed method,and the measurement technique is used to obtain the internal impedance of the DC bus plane as the excitation source of the radiation antenna during the operation of the frequency converter.Finally,a high frequency input impedance measurement platform is built in this paper to validate the proposed the input impedance models for the DC bus plane and the switching transistor drive back circuit.A radiation EMI measurement platform is built in this paper to validate the proposed radiation EMI models for the DC bus plane and the switching transistor drive back circuit.