Solution 5.8.1.36
G
H
C
R
+
-
Figure 1: Feedbackconguration
For the system shown above
GH(s)=
K(s+1)
s
2
(s +3)(s+100)
We don't expect break-in or break-out points, but wecheckanyway. The
data are shown in Table 1. From Table 1 weseethat there are no break-in
s -1.1 -1.2 -1.3 -1.4 -1.5 -1.6 -1.8 -2.2 -2.4 -2.8
K 2274 1280 945 773 664 460 477 315 241 85
Table 1: Gain along real axis
or break-out points. There are four poles and one zero so there are three
asymptotes. The asymptotes intersect the real axis at
i
=
;3;100 + 1
3
= ;34:
The root locus shown in Figure 2 was generated by the MATLAB dialogue:
EDU>K=linspace(0,1000,1000);;
EDU>gh=zpk([-1],[0 0 -3 -100],10)
Zero/pole/gain:
10 (s+1)
-----------------
1
-120 -100 -80 -60 -40 -20 0
-10
-8
-6
-4
-2
0
2
4
6
8
10
Real Axis
I
mag
A
x
i
s
Figure 2: MATLAB generated root locus
s^2 (s+3) (s+100)
EDU>rlocus(gh,K)
EDU>print -deps rl58136.eps
EDU>
2