Electric drive excitation control for improved performance of hot rolling mill finishing groups

Abstract

The study presented in the paper investigates rigorously the methods for enhancing the performance of interconnected electric drives within the finishing group of a hot rolling mill. In particular, it examines the impact of supply voltage fluctuations on drive precision and the interactions mediated by the rolled metal strip. A detailed analysis of the existing power supply system identifies the primary causes of dynamic deviations in drive operation.
A combined angular velocity control system is proposed to regulate the excitation of DC electric motors. The adaptive control strategy modulates magnetic flux during grid voltage drops, thereby reducing speed fluctuations and minimising tension inconsistencies in the inter-stand gaps. Unlike conventional systems that disregard supply voltage variations, the adaptive approach significantly improves the stability of the rolling process.
A mathematical model of the system, incorporating second- and third-order elastic couplings arising from both mechanical and electromagnetic interactions among the drives, is developed. Numerical simulations conducted in MATLAB/Simulink validate the efficiency of the proposed method. Optimal values for the relative reduction in the magnetic flux are determined to minimise discrepancies in drive currents and strip elongation. The results confirm that implementing adaptive control enhances system stability, improves rolling quality, and reduces the load on the power supply, thereby supporting its adoption in rolling mills operating under unstable grid voltage conditions.