A Closed Loop Parameter/Deadtime Estimation Technique

Processes with large deadtime to time constant ratios have traditionally proven difficult to control effectively. In practice, PID controllers (tuned to assure robustness at the expense of performance) are generally employed for the control of these processes. Conceptually, better performance is achievable through deadtime compensation using a Smith Predictor or Model Based Controller. Unfortunately, these techniques are rarely used in practice due, in-part, to unfamiliarity of technicians and operators with the tuning of these controllers. Recent work in self-tuning control has had little impact on the control of large deadtime processes. This can be attributed to reliance of most self-tuning controllers on the PID algorithm and the absence of techniques for the identification of process deadtime. This paper describes a model based control algorithm that directly incorporates deadtime compensation, and a novel closed loop process identification technique capable of identifying process deadtime directly. This combination provides an effective system for the control of large deadtime process. The resulting controller is easy to implement and commission. Its auto-tuning feature provides a simple mechanism for retuning the controller on a periodic basis. Extensive simulation results and preliminary field test results are presented in addition to a brief description of the controller and auto-tuner.