Solution 5.8.1.33
G
H
C
R
+
-
Figure 1: Feedbackconguration
For the system shown above
GH(s)=
K(s+2)
(s+1+j)(s+1;j)(s+20)(s+40)
Tosketch the root locus, wecompile the data shown in Table 1, which
determine if there are break-in or break-out points. From Table 1 wesee
s -19 -17 -13 -10 -8.5 -8 -7.5 -4.5 -4 -3.5 -3
K 401 1182 2491 3075 3191 3200 3194 2916 2880 2911 3145
Table 1: Gain alonbg real axis
that ther is a break-out pointnears = ;8. That means there must be a
break-in pointtothe rightofs = ;8. There are four poles and one zero so
wehave three asymptotes at 60
,140
and 300
. The asymptotes intersect
the negativerealaxis at
s =
;1;1;20;40+ 2
3
= ;20:
The completed root locus is shown in Figure 2. The root locus shown in
Figure 3 was generated by the MATLAB dialogue:
EDU>K = linspace(0,2000,200);;
EDU>gh = zpk([-2],[0 -1 -20 -40],10)
1
X
XX
X
Re(s)
Im(s)
-1
-2-20-40
Figure 2: Sketchofrootlocus
2
-50 -40 -30 -20 -10 0 10
-25
-20
-15
-10
-5
0
5
10
15
20
25
Real Axis
I
mag
A
x
i
s
Figure 3: MATLAB generated root locus
Zero/pole/gain:
10 (s+2)
---------------------
s(s+1) (s+20) (s+40)
EDU>rlocus(gh)
EDU>print -deps rl58133.eps
EDU>
3