Smith-principle-based PID-type Control

It has been shown in the previous chapter that Smith-predictor-based schemes are very effective for processes with dead-time. On the other hand, PID controllers are the most widely used controllers in industry (Astrom and Hagglund in Automatic Tuning of PID Controllers, Instrument Society of America, Research Triangle Park, 1988 and in PID Controllers: Theory, Design, and Tuning, Instrument Society of America, Research Triangle Park, 1995). In this chapter, a control scheme which combines their advantages as proposed by Zhong and Li in Ind. Eng. Chem. Res. 41(10), 2448–2454 (2002) is described. The controller is inherently a PID-type controller in which the integral action is implemented with a delay unit rather than a pure integrator while retaining the advantage of the Smith predictor, i.e., the Smith principle. The set-point response and the disturbance response are decoupled from each other and can be designed separately. Another advantage of this control scheme is that the robustness is easy to analyse and can be guaranteed explicitly, compromising the robustness with the disturbance response.