We have noted throughout this text that it is important to tune controllers to be robust. By robust, we mean that a controller can tolerate a certain amount of change in the process parameters without causing the feedback system to go unstable. The gain and phase margins presented in Section 7.5 quantify the amount of uncertainty that can be tolerated.
To illustrate the relationship between gain and phase margins and the model parametric uncertainty that can be tolerated, we consider the following first-order + time-delay process.
The nominal process model is
Let Δk and Δθ represent the additive uncertainty in the ...