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CHAPTER 1OVERVIEW OF
CONTROL SYSTEM© Muhammad Faizal Ismail JKE, PPD, UTHM
Outline:
• Introduction
• Control System Concept
• Type of Control System
• Control System Classification
• Control System Design
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1.1 INTRO – OBJECTIVE
AfterAfterAfterAfter completingcompletingcompletingcompleting thisthisthisthis chapter,chapter,chapter,chapter,studentstudentstudentstudent willwillwillwill bebebebe ableableableable totototo ::::
• Define the basic features andconfigurations of control systems
• Describe the open/closed-loopcontrol system
• Learn control system applications
• Describe a general process fordesigning a control system
1.2 CONTROL SYSTEM CONCEPT
What is Control System?
• A system that provides anoutput or response for a giveninput
Simplified description of a control system
• Can you give an example?
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1.2.1 EXAMPLES
aaaa.... Early elevators were
controlled by hand ropes or an
elevator operator. Here, a rope
is cut to demonstrate the
safety brake, an innovation in
early
elevators;
bbbb.... Modern Duo-lift elevators
make their way up the Grande
Arche in Paris, driven by one
motor, with each car
counterbalancing the other.
Today, elevators are fully
automatic, using control
systems to regulate position
and velocity.
ROVER WAS BUILT TO
WORK IN CONTAMINATED
AREAS AT THREE MILE
ISLAND IN MIDDLETON,
PA, WHERE A NUCLEAR
ACCIDENT OCCURRED IN
1979. THE REMOTE
CONTROLLED ROBOT ’S
LONG ARM CAN BE SEEN
AT THE FRONT OF THE
VEHICLE.
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1.3 WHAT IS SYSTEM?
• Definition: A combination of components or subsystems that act together and perform a certain objectives.
• Systems interact with their environment across a separating boundary.
• The interaction is defined in terms of variables.
– System inputs
– System outputs
– Environmental disturbance
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1.4 CONTROL SYSTEM COMPONENT
Block
Diagram
Electrical
Hydraulic
Pneumatic
Mechanical
Definition:Definition:Definition:Definition:
An interconnection
of
COMPONENTS
forming a system
configuration
that will provide
a desired system
response
Mathematical
Model
1.5 GENERIC BLOCK DIAGRAM OF CONTROL
SYSTEM
Block
diagrams of
control
systems:
a. open-loop
system;
b. closed-loop
system
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1.6 TERMS OF BLOCK DIAGRAM
• Input : desired response
• Output : actual response
• Controlled Variable : The quantity or condition that is measured and controlled (normally in the output)
• Manipulated Variable : The quantity or condition that is varied by the controller to adjust the controlled variable.
• Controller : Measuring the controlled variable and applying the manipulated variable to correct deviation of the measured value (output) from a desired value (input).
• Disturbance : Signal that affect the value of the output.
• Plants : Any physical object to be controlled a plant such as a mechanical device, a heating furnace, a chemical reactor or a spacecraft).
• Process : Operation to be controlled . Eg : Chemical , economic and biological process.
• Summing Junction / Feedback Control : to represent addition or subtraction of signals / an operation that, in the presence of disturbances, tends to reduce the difference between output of the system and reference input.
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1.7 TYPE OF CONTROL SYSTEM
• The control system can be described into
two configuration:
a)a)a)a)OPENOPENOPENOPEN LOOPLOOPLOOPLOOP
b)b)b)b)CLOSEDCLOSEDCLOSEDCLOSED----LOOPLOOPLOOPLOOP
1.7.1 OPEN LOOP CONTROL SYSTEM
• Those systems in which the outputs has no
effect on the control action.
• The output is not compared with the
reference input ( no feedback ).
• Practical example : Washing machine.
Soaking, washing and rinsing in the washer
operate on a time basis. The machine does
not measure the output signal, that is the
cleanliness of the clothes.
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1.7.2 OPEN LOOP CONTROL SYSTEM
EXAMPLE
AMPLIFIER
Power
Supply High
power
+V
-V
0V
Input signal
Low
power
MOTOR
GEARS
θO
Output
response
1.7.2 OPEN LOOP CONTROL SYSTEM
EXAMPLE
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1.7.3 ADVANTAGE & DISADVANTAGE OF OPEN
LOOP CONTROL SYSTEM
Advantages Disadvantages
1. Stability not a major problem
2. Cheaper than closed loop
system
3. Can be used even if output
cannot be measured
4. Easier to maintain
1. Changes in system or
disturbance cause errors
2. No longer accurate when the
system is disturb. Needs
calibration to maintain
accuracy (Periodic calibration
is required)
3. Low bandwidth – slow
response
1.7.4 CLOSED LOOP CONTROL SYSTEM
• Also known as feedback control system.
• In a closed loop control system the
actuating error signal, which is the
difference between the input signal and the
feedback signal, is fed to the controller so
as to reduce the error and bring the output
of the system to desired value.
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1.7.5 ADVANTAGE AND DISADVANTAGE OF
CLOSED LOOP CONTROL SYSTEM
Advantages Disadvantages
1. Reduced sensitivity to
disturbances inputs and
parameter changes.
2. Can stabilize an open-loop
unstable plant.
3. Can change system dynamics
speed of response, accuracy,
reduce effects of nonlinearities
4. Highly accurate due to corrective
actions
5. High bandwidth – fast response
1. More complex (Increased
complexity and cost)
2. Risk of instability (stability is
major problem)
1.7.6 CLOSED-LOOP CONTROL SYSTEM
EXAMPLE
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1.7.6 CLOSED-LOOP CONTROL SYSTEM EXAMPLE
1.7.6 CLOSED-LOOP CONTROL SYSTEM
EXAMPLE
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1.7.6 CLOSED-LOOP CONTROL SYSTEM
EXAMPLE
1.7.6 CLOSED-LOOP CONTROL SYSTEM EXAMPLE
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1.7.6 CLOSED-LOOP CONTROL SYSTEM
EXAMPLE
1.7.6 CLOSED-LOOP CONTROL SYSTEM
EXAMPLE
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1.8 FEEDBACK AND ITS EFFECT
• Feedback system is a system that maintains arelationship between the output and somereference input by comparing them and using thedifference as a means of control.
• Feedback is used to reduce the error betweenreference and the system output.
• The feedback has effects on performancecharacteristics as
– Stability
– Overall gain
– Noise (external disturbance).
1.8 FEEDBACK AND ITS EFFECT
Response of a
position control
system
showing effect
of high and low
controller gain
on the output
response
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• Single input single output (SISO)
• Multiple input multiple output (MIMO)
1.9 CONTROL SYSTEM CLASSIFICATION
1.9 CONTROL SYSTEM CLASSIFICATION
• Linear
• Non-linear
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• Time-variant
- The parameters of this control system donot change with time, e.g. R, L, C.
• Time-invariant
- The parameters of this control systemchange with time. It is difficult to analyze,e.g. resistance winding of a DC motorvaries when the temperature rising, fighteraircraft.
1.9 CONTROL SYSTEM CLASSIFICATION
• Analog
- All signals in this system are in the form of analog (continuous) signal.
• Digital (Discrete time)
- A digital computer is used as the controller in the system
1.9 CONTROL SYSTEM CLASSIFICATION
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• Process Control
1.9 CONTROL SYSTEM CLASSIFICATION
• Sequential Control– The operations of this control system are
performed in orders which are already setbefore.
– For example in an automatic washing machine,the operations of filling the tube, washing theclothes, draining the tube, rinsing the clothes,and spinning the clothes are already set.
1.9 CONTROL SYSTEM CLASSIFICATION
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1.10 ANALYSIS AND DESIGN
OBJECTIVES
• Three major objectives of systems analysisand design are :
– Producing the desired transient response
– Reducing steady state error
– Achieving stability
1.11 CONTROL SYSTEM DESIGN
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Summary of today’s lesson?
You have learn:
• The definition of control system.
• The components of control system.
• Block diagram.
• Type of control system.
• How to design a control system.
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