Use of Modified Relay Techniques for the Design of Model Based Controllers for Chemical Processes

In this paper the possibility of using relay techniques to build parametric models for the design of advanced controllers is analyzed. A modified relay technique (ATV+ method), which requires more experimental runs and can lead to the design of high-order controllers, is compared with the 'two-channel relay' (TCR) technique, which requires simpler experimental tests and leads to PI/PID control. The comparison is carried out for a large number of typical process dynamics by considering ease of application, duration of experimental tests, and achievable performance. For a quantitative evaluation of these features, several indexes, are defined and simulations of time responses are analyzed. As a synthetic conclusion, performance can be largely improved by adopting the ATV+ method, with model-based controllers, at the expense of a longer duration of experiments. The time required for TCR depends on initial knowledge of the process. This paper gives more details to quantify the tradeoff between performance and times. The presented results can be used as a guideline for the process control engineer to help in the choice of the more suitable technique, according to the real needs of the plant. In this paper the possibility of using relay techniques to build parametric models for the design of advanced controllers is analyzed. A modified relay technique (ATV+ method), which requires more experimental runs and can deal to the design of high-order controllers, is compared with the `two-channel relay' (TCR) technique, which requires simpler experimental tests and leads to PI/PID control. The comparison is carried out for a large number of typical process dynamics by considering ease of application, duration of experimental tests, and achievable performance. For a quantitative evaluation of these features, several indexes are defined and simulations of time responses are analyzed. As a synthetic conclusion, performance can be largely improved by adopting the ATV+ method, with model-based controllers, at the expense of a longer duration of experiments. The time required for TCR depends on initial knowledge of the process. This paper gives more details to quantify the tradeoff between performance and times. The presented results can be used as a guideline for the process control engineer to help in the choice of the more suitable technique; according to the real needs of the plant