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Root Locus

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EXPERIMENT NO:9

PERFORMANCE ANALYSIS USING ROOT-LOCUS METHOD.

AIM

Plot the root locus of the given transfer function to analyse the following using simulation:

A. Verification of the critical gain with the theoretical values.


B. The effect of controller gain K on the stability.
C. The sensitivity analysis by giving small perturbations in given poles and zeros
D. The effect of the addition of poles and zeros on the given system.

THEORY
Root-locus defines as a graph of the poles of the closed-loop transfer function as the system
parameter, such as the gain is varied The root locus of an (open-loop) transfer function is a
plot of the locations (locus) of all possible closed-loop poles with some parameter, often a
proportional gain , varied between 0 and . The figure below shows a unity-feedback
architecture

G(s)

The closed-loop transfer function in this case is:

and thus the poles of the closed-loop system are values of such that 1+K G(s)=0.
PLOTTING THE ROOT LOCUS OF A TRANSFER FUNCTION
Aim 1.
Verification of the critical gain, wo with the theoretical values
AIM : 2
The effect of controller gain K on the stability.

K=1
STABLE SYSTEM K=10
FREQ -2.83 rad/sec STABLE SYSTEM
FREQ -2.83 rad/sec
K=48
Marginally STABLE
K=40 SYSTEM
STABLE SYSTEM

K=60
unSTABLE SYSTEM

Value of k poles Damping overshoot frequency stability


ratio

Aim 3- The sensitivity analysis by giving small perturbations in given


poles and zeros
poles TF RiseTime SettlingTime Oversho PeakTi
ot me
Aim 4
The effect of the addition of poles and zeros on the given system.

Effect of addition of poles =>

i) Root locus shift towards right half of the s-plane

ii) system stability relatively decreases

Effect of addition of zeros =>

i) Root locus shift towards left half of the s-plane

ii) system stability relatively increases


PROGRAM

clc
s=tf('s')
gh=1/((s)*(s+2)*(s+4))
k=1
t=gh*k
den=[1 6 8 0]
poles=roots(den)
pzmap(t)
m=feedback(gh*k,1)

for k = 1:10:110;
pzmap (feedback(gh*k,1));
hold on;
end
figure
rlocus(t)
stepinfo(m)
sisotool(gh)

RESULT

Root Locus Of The Given Transfer Function Is Ploted In Matlab And Analysed The Given Aims

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