Advanced Electric Drive Control System of Continuous Hot-Dip Galvanizing Line

Abstract

The study is concerned with a continuous hot-dip galvanizing line, where the electric drives of the main devices are interconnected through the processed strip. This interconnection and certain elastic elements of the main devices determine the probable tension variations in the strip, which lead to process disruptions and degradation of surface condition. The variations result from the fact that the electric drive control systems of those devices that are installed between the accumulator and the furnace section are constructed following the drive torque control principle. With such a configuration, a speed controller is inactive in the normal operation mode; therefore, these electric drives do not respond to changes in speed and let through the disturbances transmitted from the adjacent devices along the strip. To study the strip tension changes in detail with regard to the mutual influence of the electric drives through the strip, mathematical modeling is carried out of three interconnected drives – the entry accumulator and tension units (TU) No. 1 and No. 2. The effect the TU speed controller settings have on damping the strip tension variations is determined. The use of an additional correcting feedback is shown to produce a beneficial effect on the torque reference of the accumulator electric drive as a function of the TU No. 1 and No. 2 speed differential. Changes are introduced to the existing control system of the operating line, industrial tests are conducted with the advanced control system for the electric drives of the entry accumulator, tension unit No. 2 and furnace rollers; favorable results are obtained. The obtained results can be used when setting up a control system for the interconnected electric drives of similar lines and units with a similar production cycle.