In this chapter we extend the ideas of modeling to include control system characteristics, such as sensitivity to model uncertainties, steady-state errors, transient response characteristics to input test signals, and disturbance rejection. We

1
Chapter 4 Feedback Control System
CharacteristicsObjectives
In this chapter we extend the ideas of modeling
to include control system characteristics, such
as sensitivity to model uncertainties,
steady-state errors, transient response
characteristics to input test signals, and
disturbance rejection. We investigate the
important role of the system error signal which
we generally try to minimize. We will also
develop the concept of the sensitivity of a
system to a parameter change, since it is
desirable to minimize the effects of unwanted
parameter variation. We then describe the
transient performance of a feedback system and
show how this performance can be readily
improved. We will also investigate a design that
reduces the impact of disturbance signals.
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Open-And Closed-Loop Control Systems
An open-loop (direct) system operates without
feedback and directly generates the output in
response to an input signal.
A closed-loop system uses a measurement of the
output signal and a comparison with the desired
output to generate an error signal that is
applied to the actuator.
3
Open-And Closed-Loop Control Systems
Error Signal
4
Sensitivity of Control Systems To Parameter
Variations
For the closed-loop case if
gt
GH
s
(
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1
1
Output affected only by H(s)

Y
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(
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R
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H
s
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D

G
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(
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G
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Open Loop
D
D

Y
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(
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G
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R
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Closed Loop
(
)
D

G
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G
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D


Y
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Y
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R
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D



1
G
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G
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H
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D
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D

Y
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R
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D


1
GH
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GH
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1
GH
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D
gt
GH
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GH
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The change in the output of the closed system
D
G
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D

Y
s
(
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R
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is reduced by a factor of 1GH(s)
2

1
GH
s
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(
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5
Sensitivity of Control Systems To Parameter
Variations
6
Example 4.1
7
Control of the Transient Response of Control
Systems
8
Control of the Transient Response of Control
Systems
9
Control of the Transient Response of Control
Systems
10
Disturbance Signals In a Feedback Control Systems
R(s)
11
Disturbance Signals In a Feedback Control Systems
12
Disturbance Signals In a Feedback Control Systems
13
Steady-State Error
14
The Cost of Feedback Increased Number of
components and Complexity Loss of
Gain Instability
15
Design Example English Channel Boring Machines
16
Design Example English Channel Boring Machines
Study system for different Values of gain K
G
Td
17
Study Examples of 4.9 - Control Systems Using
MATLAB And Apply concepts performing Lab 3