ABSTRACT
As we know, the transfer functions which characterize the classic control scheme (shown in Figure 11.1) are:
Y (s)
D(s) =
1 + C(s)P (s)H(s) (11.1)
Y (s)
R(s) =
C(s)P (s)
1 + C(s)P (s)H(s) (11.2)
Y (s)
N(s) = − C(s)P (s)H(s)
1 + C(s)P (s)H(s) (11.3)
The analysis of these transfer functions reveals that some of the typical requirements of a control system involve specific conflicts. For example, the requirement of input tracking requires a large bandwidth, but this implies a deterioration in performance in terms of rejection of the measurement noise n(t) within the bandwidth so that noise is not very attenuated. Conversely, the requirements of noise d(t) rejection, of parametric insensitivity and input tracking are not in conflict with each other.
