Overcoming Difficulties in the Application of Self-Tuning Controllers

Self-Tuning Regulators are able, in principle, to control uncertain systems and have been used in a number of experimental facilities and industrial plants. However, potential practical problems have prevented the full acceptance of these controllers in industry; these include difficulties in choice of parameters, method of start-up, long-term operation, variable time delay, valve saturation, and sudden changes in the system. Using a variable forgetting factor, an extended horizon for control and a simplified start-up procedure, we have developed a robust, general-purpose algorithm which is suitable for most single-input, single-output applications. Flow, pressure and level control loops were implemented with a near-arbitrary set of parameters on a large pilot plant. With this formulation, no practical difficulties were experienced, even in pathological situations; a similar performance is expected for other applications in an industrial environment and the algorithm is recommended for general use.