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- Pedersen, Lars Malcolm
(författare)
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Modeling and Control of Plate Mill Processes
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis two processes have been modeled and controlled, namely the plate thickness control and the slab temperature control. The classical solution for the thickness control problem can't handle asymmetric hardness variations and the estimation of the controlled output introduces stability problems. A nonlinear multivariable model for the thickness control system is derived. The parameters of the model for the rolling mill are identified using data from The Danish Steel Works Ltd. and the model is used for designing a nonlinear multivariable thickness control algorithm. The algorithm is evaluated using computer simulations and the new controller is able to handle the asymmetric case and gives a more accurate thickness control compared to the existing control system. The new control strategy is also found to be stable. The task of the slab temperature controller is to ensure a high furnace throughput, and a proper heating quality while minimizing the energy consumption. Models for the slab and furnace temperatures are identified using data collected during normal production at The Danish Steel Works Ltd. A new way of obtaining parameters for the existing slab temperature control system is described. Furthermore, a nonlinear controller is designed which it is shown to be is globally asymptotically stable. The performance of the linear and nonlinear controller are compared using computer simulations which show that the performance of the nonlinear controller is superior to the performance of the linear controller. The linear slab temperature controller design has been implemented in the slab temperature control system at The Danish Steel Works Ltd. The experimental results indicate that the new controller parameters have lead to a 10% increase in furnace capacity, with unchanged heating quality. Data from the reheat furnace no. 2 indicate that the energy consumption has not been increased by the adjustments.
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- Pedersen, Lars Malcolm, et al.
(författare)
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Multivariable controller design for hot rolling mill
- 1998
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Ingår i: IEEE Trans. on Control Systems Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-6536. ; 6:2, s. 304-312
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a controller design for a hot rolling mill. The main purpose of the algorithm is to improve the control of the cross-width thickness profile of the plates. This is obtained by designing a controller which makes independent thickness control possible at the two sides of the rolling mill. This is obtained by first linearizing the positioning systems using feedback linearization and then using linear quadratic eigenspace design on the linearized multivariable system. Integral control is included to ensure zero stationary thickness error. The design is done using derived dynamical multivariabl models. To ensure that the design is stable, the stability of the system is investigated using the small gain theorem. The performance of the controller is evaluated using models estimated from data from the hot plate mill at The Danish Steel Works Ltd.
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- Pedersen, Lars Malcolm, et al.
(författare)
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Multivariable Controller Design for Hot Rolling Mill
- 1996
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Ingår i: IFAC Proceedings Volumes. ; 29:1
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Konferensbidrag (refereegranskat)abstract
- This paper concerns the controller design for the hot rolling mill at the Danish Steel Works Ltd. The design is done using derived dynamical multivariable models. The main objective of the design is to separate the two sides of the rolling mill. This is obtained by first linearizing the positioning system using feedback linearization and then using eigenspace design on the linearized multivariable system. To ensure that the design is stable, the stability of the system is investigated using the small gain theorem. The performance of the controller is evaluated using estimated models based on data from the plate mill.
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- Pedersen, Lars Malcolm, et al.
(författare)
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On the reheat furnace control problem
- 1998
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Ingår i: IEEE Xplore : Proceedings of the 1998 American Control Conference. ACC - Proceedings of the 1998 American Control Conference. ACC. - 0780345304
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Konferensbidrag (refereegranskat)abstract
- The purpose of this paper is to develop a model and control algorithm for the slab temperature control problem, which is the control of a number of steel blocks (slabs) passing through a furnace burner zone. The slab temperature is controlled by varying the zone temperatrure. First a model for a single slab passing through the furnace is developed and the parameters are estimated. Data from the reheat furnace no. 2 at The Danish Steel Work Ltd. is used for the identification. Based on the slingle slab model a model for all slabs in a burner zone is constructed. The controllability of this model is analyzed and it is concluded that problems can arise if the temperature of two or more slabs are equal. A quadratic error function for the slab temperature is defined. From this error function and the constructed model a nonlinear controller is designed to minimize the vlaue of the error function. The stability of the control law is analyzed and it is concluded that the controlled system is stable.
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- Pedersen, Lars Malcolm, et al.
(författare)
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Optimization of Plate Thickness Controller
- 1998
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Konferensbidrag (refereegranskat)abstract
- The purpose of this paper is to describe the optimization of the thickness control system on the hot rolling mill at The Danish Steel Work Ltd. The optimization is done by replacing the existing linear analog thickness controller with a nonlinear digital controller.
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- Pedersen, Lars Malcolm, et al.
(författare)
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Thickness control for a plate mill
- 1998
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Ingår i: IFAC Proceedings Volumes : 9th IFAC Symposium on Automation in Mining, Mineral and Metal Processing (MMM 98) - 9th IFAC Symposium on Automation in Mining, Mineral and Metal Processing (MMM 98). ; 21:23, s. 331-336
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Konferensbidrag (refereegranskat)abstract
- The purpose of this paper is to describe the design of a multivariable control law for a hot plate mill. The design is performed on models adapted to the plate mill at The Danish Steel Work Ltd. The model for the rolling mill is divided into nonlinear models for the hydraulic systems performing the thickness control and a multivariable linear model for the rolling stand. The parameters of the models are found using measurements from the rolling mill at The Danish Steel Work Ltd. Most of the measurements are collected during rolling, but plate thickness measurements are performed after rolling using special equipment. In general, good agreement is obtained between measurements and model outputs. The multivariable nonlinaer model is used for designing a multivarialbe thickness control law which can be seen as an unified approach to control mean thickness and plate wedge. The result is a second order nonlinear controller with rolling forces and roll positions as inputs and control signal to the servo valves as outputs. Since it is not possible to implement the multivariable control law for the time being, the multivariable control law is simplified with the purpose of using it as a basis for an optimization of the existing thickness control equipment at The Danish Steel Works Ltd. This optimization can be seen as the first step in the practical verification of the multivariable control law.
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