Introduction to Control System

[ECE 2010]
Dr. R.K.Mugelan, Asst. Professor (Sr), SENSE, VIT

Course Outline
 Objective
 To give an overview of the fundamental concepts in
control systems and their applications
 Outcome
 Ability to apply mathematics and science in engineering
applications
 Understanding of the subject related concepts and of
contemporary issues
 Design thinking capability
Dr. R.K.Mugelan, Asst. Prof. (Sr), SENSE, VIT
2

Course Content
3
 Module:1 Introduction
 Module:2 Mathematical Modelling of Physical Systems
 Module:3 Controller and Compensator Design
 Module:4 Time Domain Response
 Module:5 Characterization of Systems
 Module:6 Frequency Domain Response
 Module:7 State Space Analysis
 Module:8 Contemporary Issues

References
4
 Norman S. Nise, “Control Systems Engineering”, John
Wiley & Sons, 6th Edition, 2010.
 I.J. Nagarth and M. Gopal, “Control Systems
Engineering”, New Age International, 5th Edition,
2011.
 K. Ogata, “Modern Control Engineering”, Pearson
Education, 5th Edition, 2011.

Mobile Apps
5
Control Systems by Engineering Apps

Introduction to Control Systems
Basic blocks – Types and Scope
6

System
7
 A system is an arrangement of or a combination of different physical
components connected or related in such a manner so as to form an
entire unit to attain a certain objective.
Output
Input

Input
8
 The stimulus or excitation applied to a control system
from an external source in order to produce the output is
called input
Output
Input

Output
9
 The actual response obtained from a system is called
output.
Output
Input

Control
10
 It means to regulate, direct or command a system so
that the desired objective is attained.

Control System
11
Combining above definitions
System + Control = Control System

Control System
12
 A control system is a system, which provides the
desired response by controlling the output.
Output
Input

Difference Between
System & Control System
13
Proper
Output
Input
Desired
Output
Input
May or May
not be Desired

Difference Between
14
 Example : Ceiling fan
Air
Flow
230V /
50 Hz
Input Output

Difference Between
15
 A Fan without blades cannot be a “SYSTEM”
 Because it cannot provide a desired/proper output i.e.
airflow
No Air
Flow
230V /
50 Hz
Input Not
desired
Output

Difference Between
16
 A Fan with blades but without regulator can be a
“SYSTEM”
 Because it can provide a proper output i.e. airflow
 But it cannot be a “Control System”
 Because it cannot provide desired output i.e. controlled airflow
Air
Flow
230V /
50 Hz
Input Output

Difference Between
17
 A Fan with blades and with regulator can be a “CONTROL
SYSTEM”
 Because it can provide a Desired output. i.e. Controlled
airflow
230V /
50 Hz
Input
Air
Flow
Output

Classification of Control Systems
18
 Based on Types of Signals
 Continuous time Control Systems
 Discrete-time Control Systems
 Based on number of inputs and outputs
 SISO (Single Input and Single Output)
 MIMO (Multiple Input and Multiple Output)
 Based on Controlling Action
 Open Loop Control Systems
 Closed Loop Control Systems

Open Loop Control System
19
 “A system in which the control action is totally
independent of the output of the system is called as open
loop system”.
 Here, the output is not fed-back to the input.
 So, the control action is independent of the desired
output.

OLCS: Example
20
 Electric hand drier
 Hot air (output) comes out as long as you keep your hand under the
machine, irrespective of how much your hand is dried.

OLCS: Example
21
 Automatic washing machine
 This machine runs according to the pre-set time irrespective of
washing is completed or not.

OLCS: Example
22
 Bread Toaster
 This machine runs as per adjusted time irrespective of toasting is
completed or not.

OLCS: Example
23
 Automatic tea/coffee vending machine
 These machines also function for pre adjusted time only.

OLCS: Example
24
 Light Switch
 lamps glow whenever light switch is on irrespective of light is
required or not.
 Volume on Stereo System
 Volume is adjusted manually irrespective of output volume level.

OLCS: Advantages
25
 Simple in construction and design.
 Economical.
 Easy to maintain.
 Generally stable.
 Ease of use.

OLCS: Disadvantages
26
 They are inaccurate
 They are unreliable
 Any change in output cannot be corrected automatically.

Closed Loop Control System
27
 “A system in which the control action is somehow
dependent on the output is called as closed loop system”.
 Here, the output is fed back to the input.
 So, the control action is dependent on the desired output.

CLCS
28

Example : CLCS
29
 Automatic Electric Iron
 Heating elements are controlled by output temperature of the iron.

Example: CLCS
30
 Guided Missile
 The Computer sends periodic commanding signals to missile w.r.t
to the radar data of the target.

Example: CLCS
31
 Perspiration

CLCS: Advantages
32
 Closed loop control systems are more accurate even in
the presence of non-linearity.
 Highly accurate as any error arising is corrected due to
presence of feedback signal.
 Bandwidth range is large.
 Facilitates automation.
 The sensitivity of system may be made small to make
system more stable.
 This system is less affected by noise.

CLCS: Disadvantages
33
 They are costlier.
 They are complicated to design.
 Required more maintenance.
 Feedback leads to oscillatory response.
 Overall gain is reduced due to presence of feedback.
 Stability is the major problem and more care is needed to
design a stable closed loop system.

Difference between OLCS & CLCS
34
 The open loop systems are
simple & economical.
 They consume less power.
 The OL systems are easier to
construct because of less
number of components
required.
 The open loop systems are
inaccurate & unreliable
 The closed loop systems are
complex and costlier
 They consume more power.
 The CL systems are not easy to
construct because of more
number of components
required.
 The closed loop systems are
accurate & more reliable.

Difference between OLCS & CLCS
35
 Stability is not a major problem
in OL control systems.
Generally OL systems are
stable.
 Small bandwidth.
 Feedback element is absent.
 Output measurement is not
necessary.
 Stability is a major problem in
closed loop systems & more
care is needed to design a
stable closed loop system.
 Large bandwidth.
 Feedback element is present.
 Output measurement is
necessary.

Feedback System
36
 There are two types of feedback −
 Positive feedback
 Negative feedback

Positive Feedback
37
 The positive feedback adds the reference input, R(s) and
feedback output.
 The transfer function of positive feedback control system
is,
𝐓 =
𝐆
𝟏 + 𝐆𝐇
 Where,
 T is the transfer function or overall gain of positive feedback control system.
 G is the open loop gain, which is function of frequency.
 H is the gain of feedback path, which is function of frequency.

Negative Feedback
38
 The negative feedback subtracts the reference input, R(s)
and feedback output thus reducing the error.
 The transfer function of positive feedback control system
is,
𝐓 =
𝐆
𝟏 + 𝐆𝐇
 Where,
 T is the transfer function or overall gain of positive feedback control system.
 G is the open loop gain, which is function of frequency.
 H is the gain of feedback path, which is function of frequency.

Feedback Systems
39
 A generalized feedback system

Feedback Systems
40
 By inspection of diagram we can add values
or rearranging
o
i
o BX
X
A
X


AB
A
X
X
i
o


1

Feedback Systems
41
 Thus
 This the transfer function of the arrangement
 Terminology:
 A is also known as the open-loop gain
 G is the overall or closed-loop gain
AB
A
X
X
i
o



1
G
gain
Overall

Feedback Systems
42
 Effects of the product AB
 If AB is negative
 If AB is negative and less than 1, (1 + AB) < 1
 In this situation G > A and we have positive feedback
 If AB is positive
 If AB is positive then (1 + AB) > 1
 In this situation G < A and we have negative feedback
 If AB is positive and AB >>1
- gain (G) is independent of the gain of the forward path A
B
AB
A
AB
A
G
1
1





Example
43
Example: Design an arrangement with a stable voltage
gain of 100 using a high-gain active amplifier. Determine
the effect on the overall gain of the circuit if the voltage
gain of the active amplifier varies from 100,000 to
200,000.
 We will base our design on our standard feedback
arrangement

Example
44
 We will use our active amplifier for A and a stable
feedback arrangement for B
 Since we require an overall gain of 100
so we will use B = 1/100 or 0.01

Example
45
 Now consider the gain of the circuit when the gain of the
active amplifier A is 100,000
B
AB
A
G
1
90
.
99
000
1
1
000
100
)
01
.
0
000
100
(
1
000
100
1










Example
46
 Now consider the gain of the circuit when the gain of the
active amplifier A is 200,000
B
AB
A
G
1
95
.
99
000
2
1
000
200
)
01
.
0
000
200
(
1
000
200
1










Example
47
 Note that a change in the gain
of the active amplifier of 100%
causes a change in the overall
gain of just 0.05 %
 Thus the use of negative feedback makes the gain largely
independent of the gain of the active amplifier
 However, it does require that B is stable
 fortunately, B can be based on stable passive components

Other Types of Control Systems
48
 Based on Linearity
 Linear Control System
 Non Linear Control System
 Based on Time
 Time varying Control System
 Time Invariant Control System

Linear Control System
49

Non-Linear Control System
50

Introduction to Control System

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