It is demonstrated that, for the best results, the Smith predictor need not necessarily be designed to eliminate time delay of a lumped-parameter process completely from the closed-loop characteristic equation. It is shown how this feature can advantageously be employed in a linear-predictor control of linear parameter-distributed processes containing in their transfer function term exp [-√(as 2 + bs + c)] which cannot be eliminated completely by a physically realizable predictor. Detailed analytical solution of the characteristic equation is given, for a heat-diffusion process compensated by an idealized form of the linear predictor. Digital simulation is then used to demonstrate how a particular rational approximation to this idealized predictor can improve the closed-loop system dynamic behaviour. Both set-point and load step changes are considered.
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