ABSTRACT
Negative feedback is a powerful mechanism for changing and controlling the dynamics of a system. Through the expert use of this type of feedback, control engineers are able to manipulate the dynamics of a huge variety of different systems, so that they behave in a way that is desirable and efficient from the point of view of the user, [1, 2, 3]. In biological systems, evolutionary pressures have led to the use of negative feedback for a wide variety of purposes, including homeostasis, chemotaxis, adaptation and signal transduction. As shown in Fig. 4.1, the principle of negative feedback is extremely simple: a feedback loop is closed around a system G and the measured output of the system y is compared to its desired value r. The resulting error signal e is acted on by a controller K, which generates an input signal u for the system which causes its output to move towards its desired value. Note that, depending on the type of system, and the level of control required, the controller K could be as simple as a unity gain or as complex as a high-order nonlinear dynamical system. Consider, for example, a simple first-order system G(s)
FIGURE 4.1: Negative feedback control scheme.
