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Automatic Control Systems
Lecture-1Basic Concepts of Classical control
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Emam FathyDepartment of Electrical and Control Engineering
email: [email protected]
What is Control System?
• A system Controlling the operation of anothersystem.
• A system that can regulate itself and anothersystem.
• A control System is a device, or set of devicesto manage, command, direct or regulate thebehaviour of other device(s) or system(s).
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Definitions
System – An interconnection of elements and devices for a desired purpose.
Control System – An interconnection of components forming a systemconfiguration that will provide a desired response.
Process – The device, plant, or system under control. The input andoutput relationship represents the cause-and-effect relationship of theprocess.
Process OutputInput
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Definitions
Controlled Variable– It is the quantity or condition that is measuredand Controlled. Normally controlled variable is the output of the controlsystem.
Manipulated Variable– It is the quantity of the condition that is varied by the controller so as to affect the value of controlled variable.
Control – Control means measuring the value of controlled variable ofthe system and applying the manipulated variable to the system tocorrect or limit the deviation of the measured value from a desiredvalue.
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Examples
Car cruise controlhttp://auto.howstuffworks.com/cruise-control3.htm
Cables
Electronically-controlled
Vacuum actuator
Other examples
• Anti-lock braking system (ABS)
– Major components of the typical ABS system
• four speed sensors (one at each wheel)
• electronic control unit (ABS computer)
• a hydraulic control unit
http://www.samarins.com/glossary/abs.html
Other examples
• Vehicle suspension system
– a system that will absorb the energy of the vertically accelerated wheel, allowing the frame and body to ride undisturbed while the wheels follow bumps in the road
http://auto.howstuffworks.com/car-suspension.htm
Types of Control System
• Natural Control System
– Universe
– Human Body
• Manmade Control System
– Vehicles
– Aeroplanes
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Types of Control System
• Manual Control Systems
– Room Temperature regulation Via Electric Fan
– Water Level Control
• Automatic Control System
– Room Temperature regulation Via A.C
– Human Body Temperature Control
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Type of systems
Control system configuration can be categorized into two:
1)Open-Loop
2)Closed-LoopControl System
Input Output
Control SystemInput Output
Open-Loop Control Systems utilize a controller or control actuator toobtain the desired response.
• Output has no effect on the control action.
• In other words output is neither measured nor fed back.
ControllerOutputInput
Process
Examples:- Washing Machine, Toaster, Electric Fan
Types of Control System Open-Loop Control Systems
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Open-Loop Control Systems
Types of Control System
• Since in open loop control systems reference input is notcompared with measured output, for each reference input thereis fixed operating condition.
• Therefore, the accuracy of the system depends on calibration.
• The performance of open loop system is severely affected by thepresence of disturbances, or variation in operating/environmental conditions.
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Type of systemsOpen-loop system
A generic open-loop system
Type of systemsOpen-loop system
Advantage ofOpen-loop system
Simple Cheap
Type of systemsOpen-loop system
Solution
Use closed-loop system
Disadvantage ofOpen-loop system
Sensitive todisturbance
Inability to correctfor disturbance
Closed-Loop Control Systems utilizes feedback to compare the actualoutput to the desired output response.
Examples:- Refrigerator, Iron
Types of Control System Closed-Loop Control Systems
ControllerOutputInput
ProcessComparator
Measurement
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Feedback Control System
Types of Control System
• A system that maintains a prescribed relationship between the outputand some reference input by comparing them and using the difference(i.e. error) as a means of control is called a feedback control system.
• Feedback can be positive or negative.
Controller OutputInput Process
Feedback
-+ error
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Type of systemsClosed-loop system
A generic closed-loop system
Type of systemsClosed-loop system
Transient response and steady-state error can be controlled by redesigning the controller. The process of redesigning is called compensating the system and the resulting hardware is a compensator
Advantage ofClosed-loop system
Less sensitive to noise, disturbances
and changes inenvironment
Transient responseand steady-state error
can be controlled easily
Type of systemsClosed-loop system
Disadvantage ofClosed-loop system
More complex More expensive
Type of systemsOpen loop vs. Closed-loop system
• How do we choose OL or CL?
– Criticality of application
• The need to monitor output
• The need to control the output
• The need for reduced error or zero error
• Cost / budget
• Safety
Multivariable Control System
Types of Control System
ControllerOutputsTemp
ProcessComparator
Measurements
HumidityPressure
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Servo System
Types of Control System
• A Servo System (or servomechanism) is a feedback control system inwhich the output is some mechanical position, velocity or acceleration.
Antenna Positioning System Modular Servo System (MS150)25
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Linear Vs Nonlinear Control System
Types of Control System
• A Control System in which output varies linearly with the input is called alinear control system.
53 )()( tuty
y(t)u(t) Process
12 )()( tuty
0 2 4 6 8 105
10
15
20
25
30
35y=3*u(t)+5
u(t)
y(t
)
0 2 4 6 8 10-20
-15
-10
-5
0
5
y(t
)
u(t)
y=-2*u(t)+1
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Linear Vs Nonlinear Control System
Types of Control System
• Linear control System Does notexist in practice.
• Linear control systems areidealized models fabricated bythe analyst purely for thesimplicity of analysis and design.
• When the magnitude of signalsin a control system are limited torange in which systemcomponents exhibit linearcharacteristics the system isessentially linear.
0 0.02 0.04 0.06 0.080
0.1
0.2
0.3
0.4
Adhesion Characteristics of Road
Creep
Adhesio
n C
oeff
icie
nt
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Time invariant vs Time variant
Types of Control System
• When the characteristics of the system do not depend upon timeitself then the system is said to time invariant control system.
• Time varying control system is a system in which one or moreparameters vary with time.
12 )()( tuty
ttuty 32 )()(
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Continuous Data Vs Discrete Data System
Types of Control System
• In continuous data control system all system variables are function of acontinuous time t.
• A discrete time control system involves one or more variables that areknown only at discrete time intervals.
x(t)
t
X[n]
n30
Deterministic vs Stochastic Control System
Types of Control System
• A control System is deterministic if the response to input is predictableand repeatable.
• If not, the control system is a stochastic control system
y(t)
t
x(t)
t
z(t)
t31
Types of Control SystemAdaptive Control System
• The dynamic characteristics of most control systemsare not constant for several reasons.
• The effect of small changes on the systemparameters is attenuated in a feedback controlsystem.
• An adaptive control system is required when thechanges in the system parameters are significant.
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Types of Control SystemLearning Control System
• A control system that can learn from theenvironment it is operating is called a learningcontrol system.
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Classification of Control Systems
Control Systems
Natural Man-made
Manual Automatic
Open-loop Closed-loop
Non-linear linear
Time variant Time invariant
Non-linear linear
Time variant Time invariant34
Examples of Control Systems
Water-level float regulator
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Examples of Control Systems
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Examples of Modern Control Systems
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Examples of Modern Control Systems
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End Of Lec 1
