Page 183 - MATLAB an introduction with applications
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168 ——— MATLAB: An Introduction with Applications
ans =
–0.1282 + 2.6357i
–0.1282 – 2.6357i
–0.1436
>> % Nyquist plot
>> num =[0 0 0 1];
>> den =[1 0.4 7 1];
>> nyquist(num,den)
>> v=[–3 3 –2 2];axis(v);axis(‘square’)
>> grid
>> title(‘Nyquist plot of G(s)’)
Nyquist Diagram
1
0.8
0.6
0.4
Imaginary Axis 0.2
0
0.2
0.4
0.6
0.8
1
1 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1
Fig. E3.19 Nyquist plot of G(s)
There are two open-loop poles in the right half s plane and no encirclement of the critical point, the closed-
loop system is unstable.
Example E3.20: For the closed-loop control system shown in Fig. E3.20, obtain the range of gain K for
stability and plot a root-locus diagram for the system.
F:\Final Book\Sanjay\IIIrd Printout\Dt. 10-03-09
