The Control System Problem
We have previously encountered the control system problem in Chapter 6:Whereas the
poles of the open-loop transfer function are easily found (typically, they are known by
inspection and do not change with changes in system gain), the poles of the closed-loop
transferfunctionaremoredifficulttofind(typically,theycannotbefoundwithout factoring
the closed-loop system’s characteristic polynomial, the denominator of the closed-loop
transfer function), and further, the closed-loop poles change with changes in system gain.
A typical closed-loop feedback control system is shown in Figure 8.1(a). The
open-loop transfer function was defined in Chapter 5 as KG(s)H(s). Ordinarily, we