Improving performance using cascade control and a Smith predictor

Many investigations have been done on tuning proportional-integral-derivati ve (PID) controllers in single-input single-output (SISO) systems. However, only a few investigations have been carried out on tuning PID controllers in cascade control systems. In this paper, a new approach, namely the use o f a Smith predictor in the outer loop of a cascade control system, is inves tigated. The method can be used in temperature control problems where the s econdary part of the process (the inner loop) may have a negligible delay w hile the primary loop (the outer loop) has a time-delay. Two different appr oaches, including an autotuning method, to find the controller parameters a re proposed. It is shown by some examples that the proposed structure as ex pected can provide better performance than conventional cascade control, a Smith predictor scheme or single feedback control system. (C) 2001 Elsevier Science Ltd. All rights reserved.