Dr.

Arshad Ali
Assistant Professor
Linear
Control Department of Electrical
Engineering
Systems
HITEC University
Topics to be Covered
• Introduction to Control Systems, Basic Terminologies

• Types of Systems and Feedback

• Modeling of Electrical and Mechanical Systems using Free Body

Diagrams

• Types of Inputs, Pole Zero Map, Transfer Functions

• Block Diagram Reduction and Transformations

• Signal Flow Graphs, Mason’s Gain Formula

• Transient Response Specifications of First Order Systems

• Transient Response Specifications of Second Order Systems

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Topics to be Covered
• Steady State Error of Different Types of Systems

• Stability of systems using Routh-Hurwitz criteria

• Frequency Response, Amplitude ratio and Phase, Bode Plots

• Bode Plots Using Exact and Approximate Methods, Systems

Identifications

• Root Locus properties and Techniques

• Introduction to PID ControlleriI i

• Design and implementation of PID

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Recommended Books
• Design of Feedback Control Systems - By Stefani, Savant, Shahian &
Hostelter (4th Edition, 2002, Oxford University Press)

• Modern Control Systems, 8th Ed - Richard C.Dorf , RobestH.Bishop

(12th Edition, 2010 Pearson)

• Control Systems Engineering – Norman S. Nise ( 7th Edition, 2015,

Wiley International)

• Modern Control Engineering – Katsuhiko Ogata (5rd Edition, 2009,

Pearson)

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Distribution of Marks

Theory (75%) Practical (25%)

 Unannounced Quizzes/  Attendance 05%
Assignments 20%  Lab Performance 40%
 Two Sessional Examinations  Mini project 30%
30% (15% each)  Viva Voce 25%
 Final Examination 50%
 Introduction to Control Systems

• Control systems plays a vital role in our day-to-day life

• Provides a background of control principles in various engineering

applications.

• Basic mathematical tools such as Laplace transform, transfer

function, block diagram, signal flow graph, mathematical modeling of
dynamic systems, time response analysis, stability of linear system,
root locus and frequency domain analysis are utilized.

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 Basic Definitions
• System: an arrangement or combination of different physical
components that are connected or related together to form an entire
unit to achieve/perform a certain objective

• Systems can be physical, economical, biological

• Control: to regulate, direct or command a system so that a certain

output is achieved.

• Control system: interconnection of components to provide a desired

function

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• Plant: a piece of equipment, set of machines functioning together
to perform a particular operation. Any physical object to be
controlled.

• E.g.: Mechanical devices, heating furnace, spacecrafts.

• Process: Progressively continuing operation which occurs in a

series of controlled actions systematically towards a particular
result. Any operation to be controlled.

• E.g.: Navigation on aircraft.

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 Basic Components

Inputs Outputs
Plant / Process
(Objective) (Results)

• Input: applied signal or excitation signal that is applied to a control

system

• Output: The actual response that is obtained from a control system due
to the application of the input

• Plant is fixed. Output produced is fixed.

• Block Diagram: identifies the major components of the systems in the

form of blocks. Shows the direction of information and energy flow
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from one component to another

 Plant with Controller

Disturbance

Inputs Plant / Outputs

(Objective) Controller (Results)
Process

• Controller: a component of the system which generates a manipulated signal

to the input to produce a desired output.

• Disturbance: a signal that tends to affect the value of the output of a system.

• Internal Disturbance: vibration, sound

• External Disturbance: Wind, surroundings, noises.

• Actuators: Apply force or torque to the physical system 10

• Sensor: Measure system behavior.

Examples

Cruise Control in Cars:

• Automobile is the Plant

• The actuator is the engine which generates propulsive forces that turn the wheel

• The Sensor is the tachometer, which measures the vehicle speed

Other example:

 Climate control

 Traction control

 Industrial Automation (Assembly lines)

 Robotics 11

 Solar Trackers
Output Signal

• Transient: instantaneous change of the input against the gradual

change of output. Physical system undergoes gradual change of
state.

• Steady State: Approximation to the command or desired 12

response. Occurs when system near the desired output.

Advantages of Control Systems
We build control systems for four primary reason:

i. Power Amplification (Gain)

• Positioning of a large radar antenna by low-power rotation of a knob

ii. Remote Control

• Robotic arm used to pick up radioactive materials

iii. Convenience of Input Form

• Changing room temperature by thermostat position

iv. Compensation for Disturbances

• Controlling antenna position in the presence of large wind 13
disturbance torque
Classification of Control Systems

Depending on the relation of the control action with the output,

any control system can be classified as:

• Open - loop system

• Closed - loop system

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 Open Loop Systems
• Output has no effect on the control action

• Output value is not measured, isolated from input

• Operates on the basis of time.

Examples: bread toaster, hand drier, traffic signals, man walking

with eyes closed

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Example of Open Loop System

Washing Machine:

• Soaking, washing and rinsing is time operated.

• Machine does not measure the output signal, cleanliness of

clothes.

• Output signal is not compared with the input

• Fixed operating conditions (time)

• Accuracy depends on calibration

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Advantages of Open Loop

• Simple in construction and design

• Used where inputs are known, disturbance is minimum and

outputs are difficult to measure

• Economic as low in cost and low power consumptions

• Easy to maintain

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Disadvantages of Open Loop

• Not accurate and reliable

• Accuracy depends on the accuracy of calibration

• Optimization is not possible

• External disturbances effect the system producing inaccurate

results

• Changes in parameters require constant recalibration

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Closed Loop Systems
• Controlling action is dependant on the output or changes in
input
• Output is fed back into the input
• Feedback signal produces error signal

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Closed Loop Systems Definitions
• Error Signal [e(t)]: Difference between the input and the feedback
signal. Fed into the controller to reduce the error and bring the output
of the system closer to the desired value.
• Input transducer sense the input physical quantity and converts it
into a form to be used by the controller [r(t)]
• Controlled Variable [c(t)]: quantity which is controlled
• Manipulated Variable [u(t)]: quantity which is varied
• Output transducer measure the output response and convert it into a
form used by the controller
• Output signal arrives back via a feedback path
• Summing junction: algebraically sums two or more signals 20
Advantages of Closed Loop
• Response is more accurate due to correction of arising errors

• Insensitive to external disturbances

• Transient response and steady state response can easily be

controlled

• Reduced effects of non-linearity

• High bandwidth, higher operating frequency zones

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Disadvantages of Closed Loop

• Complicated in design
• Complex and costlier
• Oscillations generates within the system
• Can get unstable in certain conditions

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A Manual Level Control System

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 Example of Closed Loop
• Objective: To control direction and speed of car

• Outputs: Actual direction and speed of car

• Control inputs: Road markings and speed signs

• Disturbances: Road surface and grade, wind, obstacles

• Possible subsystems: The car alone, power steering system,

breaking system

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Functional block diagram:
Desired Actual
course course
of travel + Error Steering of travel
Driver Automobile
Mechanism
-

Measurement, visual and tactile

Time response:

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 Types of Feedback:
Positive feedback:
• When a system tends to
increase output
• Small disturbances increase
the magnitude of
perturbations (Changes in
normal State)
Examples:
• Tends to cause system
Amplifier oscillations in
instability
electronics, microphone and
• Results in exponential speaker resonance.
growth, increasing
oscillations

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 Types of Feedback:
Negative Feedback:
• System tends to reduce output
• Results of a process causes the
operation to reduce change
• Makes system self regulating, more
stable
• Reduces the effects of fluctuations

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