| With the development of coal mines in the direction of intelligence and precision,various underground communications and sensor equipment are required to be safe,fast,and reliable,which puts forward higher requirements for the underground electromagnetic environment.However,it is found through field measurement that the electromagnetic interference generated by the variable frequency speed regulation system often exceeds the limit of the national standard,so the research on its interference characteristics is of great significance.This article first analyzes the operating conditions of the variable frequency speed regulation system,and obtains the principle of IGBT switching.Then,the mechanism of electromagnetic interference is studied from two aspects of conduction and radiation,and the cause of interference and the propagation path are introduced.Finally,the method of combining the method of moment and antenna theory,referring to the geometric structure of the actual variable frequency speed control system,builds an antenna model of the mine variable frequency speed control system in the electromagnetic simulation software FEKO to calculate the maximum possible occurrence of the speed control system Radiated interference situation.The calculation results of the model are analyzed from two aspects: the near field and the far field.For the near field,the enclosure of the frequency converter limits the high field strength inside,which plays a good shielding effect.The field strength outside the enclosure of 0.5m meets the limit requirements;the outgoing cable plays a role in the overall radiation of the frequency conversion speed control system.The main function is that the field strength radiation is reduced by spreading around the cable as the center.For the far field,the direction of the radiation lobe is closely related to the frequency.At low frequencies,it is evenly distributed in the horizontal direction of the X and Y axes.At high frequencies,it mainly propagates in the direction of 45°between the incoming and outgoing cables and the Z axis.Combining the calculation results and the analysis of the interference mechanism,two ways to suppress the common mode conducted electromagnetic interference are proposed to increase the common mode impedance;the calculation and comparison of the interference conditions under ideal shielding,braided mesh shielding and unshielded proves the braided mesh shielding For the effectiveness of cable radiation suppression.Under the regulations of the relevant measurement standards,the radiated field strength of the 0.1-30 MHz frequency band,the overall radiated field strength of the speed control system in the 30-1000 MHz frequency band,and the conducted interference in the 0.15-30 MHz frequency band at the typical position under half-load and full-load operation are respectively measured.Case.The measurement results show that:(1)The calculation results of the antenna model and the measurement results have a high degree of fit,and the antenna model is effective;(2)Under half load,the field strength distribution at the front of the inverter is relatively consistent,and the overall field strength of the outlet cable terminal is important.The field strength distribution curve at the installation place of the rectifier and the inverter heat sink is almost the same if it is larger than the inlet end.From the comprehensive field strength distribution of each position,the high field strength is distributed at the frequency below 1MHz;(3)Under full load,The distribution trend of the field strength at each typical location is more consistent with that under half load,and the amplitude is higher than that under half load;(4)The overall radiation in the high frequency band is slightly higher than the limit due to environmental noise at individual frequency points.Most of the other frequency points outside the value meet the specified limit;(5)The conducted electromagnetic interference on the power supply side exceeds the limit at multiple frequency points below 1MHz,and the maximum amplitude appears in the 0.2-0.3MHz frequency band,reaching 133 d BμV/m.The paper has 63 figures,9 tables,and 54 references. |
PDF Full Text Request