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

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Introduction to Control System

Similar to Introduction to Control System (20)

Recently uploaded

Recently uploaded (20)

Introduction to Control System