Abstract
The thesis describes how a Direct Torque Control (DTC) drive technology has been modified to provide improved control of a Crop Cobble Shear (CCS) system in a steel rolling mill. The CCS is a highly dynamic load and requires a high performance torque control drive. When the original DTC is used to control the shears in normal cutting modes (such as head cut and tail cut) the system functions well providing well defined and accurate cut lengths. However, during the CCS cobble cutting mode, depending on the bar length, the original DTC drive experiences overcurrent faults that cause production downtimes. A model of the DTC induction motor drive system has been developed and provides the parameters for a simulation model. This allowed the CCS operation to be analyzed and modified to improve performance. The simulated DTC induction motor drive is compared with the original existing system from a steel plant. Measurement data from the original system in the steel mill are favorably compared with simulation results. This comparison shows that the system has been successfully simulated to determine a suitable approach to improving the CCS operation.
Once new control strategies had been identified, simulations of the modified system have been carried out. These simulations predicted that the DTC performance in CCS mode would be improved by reducing or eliminating the overcurrent faults. Follow these simulations, the modifications were made to the original system and measurements were carried out to verify the improvement. These measured and simulated results are also shown in the thesis. The thesis provides conclusion on this project.