Modified Smith-predictor multirate control utilizing secondary process measurements

Abstract

The Smith-predictor is a well-known control structure for industrial time delay systems, where the basic idea is to estimate the nondelayed process output by use of a process model, and to use this estimate in an inner feedback control loop combined with an outer feedback loop based on the delayed estimation error. The model used may be either mechanistic or identified from recorded data. The paper discusses improvements of the Smith-predictor for systems where additional secondary process measurements without time delay are available as a basis for the estimation. The estimator may then be identified from recorded data also in the common case when the primary outputs are sampled at a lower rate than the secondary outputs. A simulation example demonstrates the feasibility and advantages of the suggested control structure.