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UBC Theses and Dissertations

Dual adaptive control of chip refiner motor load Allison, Bruce James


A characteristic of wood chip refiners is that the incremental gain between the motor load and the plate gap is subject to a slow drift due to plate wear and sudden changes in sign due to pulp pad collapse. A pad collapse can be caused by a change in operating point, or may occur suddenly due to a feed rate or consistency disturbance. This poses a problem for fixed-parameter linear controllers which may actually accelerate pad collapse and induce plate clashing as a result of getting caught in a positive feedback loop. The objective of this thesis is to develop a reliable chip refiner motor load controller and to test it out on an industrial refiner. The problem is approached from a fault detection and control viewpoint and the proposed algorithm consists of an improved parameter estimator and a controller containing "dual" features. The role of the improved estimator is to track both drifts and jumps in the parameters. The use of active learning or probing in the controller is justified by the fact that the parameter estimates are key to identifying a pad collapse, and that probing targets a portion of the input energy at continuously identifying these parameters. Since there still does not exist a general dual controller design methodology, the main challenge was to extend existing suboptimal approaches to handle realistic dynamics including deadtime and correlated disturbances. To track both slow and fast changes in the system parameters, a multi-model approach called adaptive forgetting through multiple models or AFMM is used. A method of modifying the AFMM to include information about what to expect in the event of a pad collapse is proposed. The main contribution of the thesis is the development of the active adaptive controller or AAC, which consists of a constrained certainty equivalence approach coupled with an extended output horizon to deal with nonminimum phase systems and a cost function extension to get probing. Finally, the AAC is combined with the AFMM, and the resulting combination is tested on an industrial refiner.

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