7.4. Closed-Loop Stability Concepts
Sections 7.1–7.3 introduced frequency response analysis, including the construction of Bode and Nyquist plots. In this section we illustrate how Bode and Nyquist plots can be used to determine the stability of a closed-loop system. We also show how to use these plots to tune controllers for robustness, that is, to be able to tolerate a given level of model uncertainty. The tests used involve information about the controller and process in open-loop. The open-loop analysis that we use in this chapter is different from that used in model-based control chapters.
Consider the case where the loop has been opened, as shown in Figure 7-10. We introduce the concept of Bode stability using the following thought experiment. ...
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