Research On Main Drive Control Methods Of Reversing Mill

As possessing the characteristics of small scale of production, less investment, small batch and a fast transform in variety specification, reversing mills are widely used in iron production. The main drive control system of a reversing mill has a great impact not only on the operating, running, and the routine maintenance of the mill, but also on the quality, varieties and specifications range of the products. Because the main drive control methods decide the performance of the system, the researching on them has important application value and theoretical significance.In this thesis, the background is the stainless steel cold-rolled production line and the object is the main drive control system of the reversing mill. The thesis analyzes the basic structure, the working principle and the control methods of the main drive control system. The main drive control system adopts the AFE three-level AC-DC-AC variable speed system, which can make the rectifier unit and the inverter unit controlled independently. Because the observer has an uncertain initial value, the rectifier has a large start-up current which may lead to the system failure, while using the virtual flux oriented vector control method. For this reason, the thesis adopts the grid voltage oriented vector control strategy to achieve a more effective control on the rectifier. However, the complex mathematical model of this method makes the controller designed difficultly. So, according to the project requirement, the thesis simplifies the rectifier model to make it easy to select the PID controller parameters. Then the phase-locked loop (PLL) technology is proposed to solve the oriented deviation problem. As a result, it achieves an effective control on the DC bus voltage and the grid power factor. For salient pole synchronous exist a big control error caused by the unsaturated magnetic circuit, while using the air-gap flux-oriented vector control method, in this thesis, the stator flux oriented vector control method is adopted to decouple the dynamic mathematical model for motor. On this basis, PID is used to control the synchronous motor speed and torque. As in the practical application of the industry, the synchronous motor’parameters are variable and its load torque changes nonlinearly, the thesis, on the basis of the vector control strategy, tries to introduce the sliding mode variable structure control method, which possesses a fast response and the insensitivity to parameters variation and load disturbance, to design the speed regulator. Finally, the control system achieves response fast and accurately to the synchronous motor torque and speed.On the basis of the above work, the thesis analyzes the performance of the main drive control system under the SMC through Matlab simulation software. The results demonstrates that the main drive control system under the SMC not only has a fast and accurate response to the set-point, starting and braking, acceleration and deceleration instructions, but also can adapt to changes in the load disturbance and the environmental parameters better. In addition, the system switches smoothly and quickly between forward and reverse running. Finally, the thesis achieves effective control of the reversible mill main drive control system.