Algorithms and Control Systems for Electric Drives of Cold Pipe-Rolling Mills
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rithms and Control Systems for Electric Drives of Cold Pipe-Rolling Mills A. N. Gorozhankina, * and M. M. Dudkina aSouth
Ural State University (National Research University), Chelyabinsk, 454080 Russia *e-mail: [email protected] Received May 27, 2020; revised May 31, 2020; accepted June 1, 2020
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. Keywords: cold pipe-rolling mills, algorithms and control structures, vector control, direct torque control DOI: 10.3103/S1068371220070068
Cold pipe-rolling mills are designed to manufacture high-quality special-purpose tubes for aerospace and power generation industries. Strict requirements for the dynamics, overload capacity, and controllability (Table 1) are imposed on the electric drives of such mills. Direct current motors and synchronous machines with an active rotor are used as electric machines in such mills. One way to improve the quality of products and energy characteristics and increasing the productivity is the change to synchronous reluctance machines. The latter are perfectly controllable owing to the direct control of all control actions and enhanced energy characteristics due to having no losses in the rotor, high overload capacity, and a low inertia moment of the rotor. The dynamic characteristics of the speed circuit in the control system of an electric drive with a synchronous reluctance machine can be improved by reducing the inertia moment of the electric machine by switching, e.g., to machines with a high ratio of the active part’s length to its diameter.
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