Analysis And Research On Harmonic Characteristics Of Typical Frequency Converters

With the development of modern industrial technology,frequency converters are widely used in all walks of life,especially in heavy industries such as metallurgy and chemicals.The core part of the converter is the rectifier bridge and inverter bridge composed of diode or fully controlled power switching tubes,such as IGBT and IGCT.The use of these power switching tubes generates a large number of low and supraharmonics.The inverter using diode rectification will inject a large number of low harmonics into the grid side,causing serious impact on the safe operation of the grid,thus the research and management of low harmonics cannot be ignored;the inverter using IGBT and other fully-controlled switching tube rectification will generate supraharmonics,however,with the development of high frequency of power electronic devices,the impact caused by supraharmonics cannot be underestimated,so the research and management of supraharmonics generation The study of the mechanism,emission characteristics and interaction effects of supraharmonics is of great significance.Firstly,the thesis analyses the harmonic characteristics of various types of converter speed control systems in combination with the structural characteristics and operating principles of general-purpose converters,multiple rectifier converters and double PWM inverters,and further analyses the impact of harmonics on the power grid and their suppression methods,while studying the sources,propagation characteristics and harmful effects of supraharmonics.Secondly,the input harmonic characteristics of 6,12 and 18 pulse wave rectifier are studied in conjunction with the structural characteristics of multiplexed rectifier circuits,and the correctness of the theoretical analysis is verified through simulation.The harmonics problem of the frequency regulation system is analysed in conjunction with the 6-pulsation rectifier and 12-pulsation rectifier converter in the Masteel heavy H-beam project,and the combination of passive filtering devices and dynamic reactive power compensation devices can effectively solve the power quality problems of the power supply system.Finally,the mechanism of supraharmonics generation and emission characteristics are analysed in the context of a dual PWM two-level converter,and the influence of filter inductance ratio,network impedance and background harmonics on the emission amplitude of supraharmonics is investigated through simulation analysis to verify the correctness of the theoretical analysis.Analysis of the supraharmonics generation mechanism and emission characteristics of a three-level converter combined with in-phase or anti-phase cascaded PWM of the carrier wave,and then the interaction effects of multiple converters with the same switching frequency and different switching frequencies are investigated in combination with a three-level converter.The correctness of the theoretical analysis of the supraharmonics generation mechanism of the three-level converter is verified through the analysis of the dual PWM three-level converter drive system on the cold-rolled pickling high distribution production line in the new area of Masteel.