| The ladle refining furnace is an industrial refining electric furnace that uses the arc heating function to produce ultra-low sulfur,ultra-low oxygen,high cleanliness and high-quality molten steel.It is an important production equipment in iron and steel smelting.During the working process of the refining furnace,it will bring reactive power impact to the power supply system and inject a large amount of harmonic current,resulting in power quality problems such as voltage fluctuation,flicker,and low power factor,which seriously affect the safe operation of other equipment.Therefore,it is of great practical significance to study and design a reasonable dynamic reactive power compensation scheme for the refining furnace to solve the power quality problem that occurs when the refining furnace is connected to the power grid.The thesis focuses on dynamic reactive power compensation devices for refining furnaces.Through an in-depth study of the treatment scheme,a harmonic and reactive power compensation solution combining a C-type secondary high-pass filter and a buck cascade static reactive power generator is adopted for engineering practice.Firstly,based on the time-varying non-linear,three-phase asymmetric load characteristics of the refining furnace,and combined with the smelting process and power supply characteristics of the refining furnace,the study of large refining furnace smelting process produces violent disturbance to the power grid,which needs to be fast reactive power compensation and harmonic treatment to improve the power quality of the power grid.Secondly,Combined with the load characteristics of the refining furnace,the key technologies of the cascaded SVG of the reactive current detection and control system are studied.Using the current detection method and decoupling phase-locked loop technology based on the double synchronous coordinate system,the positive and negative double sequence current decoupling control and PI+repetitive current control strategy are proposed to realize the fast and accurate tracking of the command current,improve the system response speed,thereby inhibiting the voltage fluctuations.In order to improve the operation reliability of cascaded SVG under the load of refining furnace,based on the traditional three-layer control of DC side voltage,the zero-sequence voltage and negative sequence current feedforward control strategies were studied,and an improved PI cascaded SVG current was proposed.The control strategy was verified on the Matlab simulation platform,and different voltage drop degrees were tested respectively,and the conclusion was obtained that the negative sequence current feedforward control is better for maintaining the voltage balance between the phases.Power support and voltage support.Finally,for the Masteel 1~#LF furnace reactive power compensation project,the parameters of the C-type secondary filter,the SVG main circuit parameters and the control system software and hardware circuit design were carried out.Combined with the application of improved control algorithms in engineering practice,it was verified that the comprehensive compensation scheme can effectively suppress harmonics and reduce voltage fluctuations,so that the power factor of the distribution network where Ma Steel 1~#LF is located reaches above 0.95 and the maximum voltage fluctuation value is reduced from 2.86%to 1.15%. |
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