Abstract
The paper analyzes the quality of current, moment and speed adjustment in high-power DC thyristor electric drives (with a capacity of more than 2000 kW), that is made with 12-pulse thyristor converters (in which valve sections have parallel connection through current-limiting inductors) and a three-winding power transformer. This type of electric drive is widely used in the metallurgical and mining industries for the main drives of hot and cold rolling mill stands, pipe mills and mine lifts. The article researches cases when individual current regulators are used for each valve section and while using one total current regulator for all valve sections. To analyze the cases, the article presents design models for thyristor electric drives automatic control systems with one and two current regulators. Based on them, the article provides automatic control drives block schemes and gives mathematical descriptions and possible models required for further experiments. In contrast to the traditional two-circuit automatic control speed drive, the schemes under consideration are characterized by having cross-links due to the mutual influence of the valve sections. Cross-links can significantly affect the quality of current regulation and electric drives speed. In the model with individual current regulators, the mutual influence of valve sections (cross-links) causes a decrease in the quality of current and speed regulation. The MATLAB /Simulink modeling showed that in this case, the current speed is reduced by 2-3 times as compared to traditional automatic control drives. Such decrease in speed in the current control circuits leads to a 1.5-2 times drop for the automatic control drive speed. In case of using one general current regulator, the mutual influence of the valve sections (cross-links) is eliminated. As a result, there is a possibility to achieve the maximum speed characteristics, normally demonstrated in traditional automatic control drives.
Keywords
control of electric variables, regulation of electric current, alternating current to direct current power converters, electromechanical systems, variable
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