Solution 5.8.1.35
G
H
C
R
+
-
Figure 1: Feedbackconguration
For the system shown above
GH(s)=
K(s+1)
s
2
(s+3)(s+10)
Tosketch the root locus, wecompile the data shown in Table 1,to de-
termine if there are break-in or break-out points. From Table1weseethat
s -2.9 -2.8 -2.7 -2.5 -2.3 -2 -1.8 -1.6 -1.4 -1.2
K 3.1 6.3 9.4 15.6 21.9 32 39.9 50.2 67.4 114
Table 1: Gain alonbg real axis
there are no break-in 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;10 + 1
3
= ;4:
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 -15],10)
Zero/pole/gain:
10 (s+1)
----------------
1
-15 -10 -5 0 5
-20
-15
-10
-5
0
5
10
15
20
Real Axis
Imag Axis
Figure 2: MATLAB generated root locus
s^2 (s+3) (s+15)
EDU>rlocus(gh,K)
EDU>print -deps rl58135.eps
EDU>
2