Control of a System with Time Delay – Chlorination of Wastewater.
Event details
| Date | 24.09.2010 |
| Hour | 10:15 |
| Speaker | Prof. O. Crisalle, Department of Chemical Engineering University of Florida, Gainesville, U.S.A. |
| Location |
ME C2 405
|
| Category | Conferences - Seminars |
Dynamic systems that exhibit a large variations in dead-time (also known as transport delay) effect are particularly challenging to control in a fashion that ensures both closed-loop stability and adequate performance. We review results characterizing the robustness of the Smith Predictor control scheme, a technique widely used in chemical engineering applications to address the challenges posed by time-delay systems. Practical experience and a vast literature record suggest that this control method may not be particularly robust. In fact, under certain conditions the control loop may become unstable when the estimated delay is affected by very small errors, a perplexing behavior. A complete framework is presented to assess in a quantitative fashion the robustness of Smith Predictor designs.
Typical municipal wastewater chlorination systems are affected by large time-varying delays. Chlorine is added as a disinfectant in a fashion that ensures adequate retention time in the basin, while satisfying regulations on its concentration at the discharge point. This talk shows that typical control schemes are unable to effectively reject the adverse effect of inlet flow rate variations that lead to significant time-delay fluctuations. Instead of implementing a Smith Predictor scheme, which may lack robustness under these circumstances, an automatic control solution that involves engineering redesign of the plant is proposed and evaluated. A new residence-time controller is advocated as a solution that involves both feedback and feedforward architectures and that can be deployed using standard PID software.
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- General public
- Free