Algorithms and Control Systems for Electric Drives of Cold Pipe-Rolling Mills

Abstract

The electric drive of a cold pipe-rolling mill operates at a low speed with great accelerations and overloads. This mode of operation dictates increased requirements for the speed and controllability. The integration of synchronous reluctance machines (SRMs) into controlled electric drives improves the productivity of the mill and the quality of products and energy performance due to good controllability, high overload capacity, absence of losses in the rotor, and low inertia of the former. The choice of algorithms and control structures significantly affects the characteristics of the electric drive. Control structures of an independently excited electric drive are considered. Pulse-width control of a voltage inverter by forming current diagrams using a spatial vector in a rotating d–q coordinate system and direct torque control (DTC) are considered as algorithms for controlling the electric converter. Taking into account the operating modes of the electric drive and the requirements imposed on it, criteria have been formulated for comparing control systems—namely, speed of the current, flux, and torque control circuits—and losses in the electric converter are estimated by the switching frequency of the power switches. According to the results of experimental studies using mathematical models, both control systems showed similar performance capabilities. It has been shown that, in DTC systems, the switching frequency of the switches and the associated losses of the semiconductor converter decrease in the torque overload zone.