1. Introduction to :Introduction to :
Control SystemsControl Systems
EngineeringEngineering
Lecture #02Lecture #02

2. Basic ConceptBasic Concept
 Control system is designed to obtain aControl system is designed to obtain a
desired output from a given input.desired output from a given input.
 Basic components :Basic components :
 Input (objective/ desired response)Input (objective/ desired response)
The excitation applied to a control systemThe excitation applied to a control system
from an external energy source.from an external energy source.
 control systemcontrol system
 output (actual response)output (actual response)
The actual response obtained for a controlThe actual response obtained for a control
system.system.

3. Purposes of Control SystemPurposes of Control System
 Power AmplificationPower Amplification
Control system is used in many systems to produce power gain or
amplification.
 Remote ControlRemote Control
Control system is the key idea for controlling robots and other
automated systems.
 Convenience of InputConvenience of Input
Control system provides the convenience of input form. For example
we do not have to put in heat to obtain heat for a temperature
control system. For this case, the input is the position on the
thermostat and the output is the heat.
 Compensation of DisturbanceCompensation of Disturbance
Control system can compensate disturbance. For example, in the
case of an antenna which is positioned in a specific direction, the
control system detects any variation in the position due to
disturbance like wind and positions the antenna back to the original
position.

4. CONTROL SYSTEMCONTROL SYSTEM
OPEN LOOPOPEN LOOP CLOSE LOOPCLOSE LOOP
 The output is notThe output is not
measured.measured.
 Control system isControl system is
independent of theindependent of the
output.output.
 System cannotSystem cannot
compensate forcompensate for
disturbance.disturbance.
 Examples : toaster,Examples : toaster,
washing machine, fan.washing machine, fan.
 System has feedback andSystem has feedback and
output is measuredoutput is measured
 System output has anSystem output has an
effect on the controleffect on the control
actionaction
 system can compensatesystem can compensate
for disturbance.for disturbance.
 Examples :air conditioner,Examples :air conditioner,
robot (arm).robot (arm).

5. Open Loop SystemOpen Loop System
 Example for antenna pointing systemExample for antenna pointing system

6. Open Loop SystemOpen Loop System
 Antenna will rotateAntenna will rotate clockwiseclockwise andand
anticlockwiseanticlockwise depending on the outputdepending on the output
signal,signal, negativenegative oror positive.positive.
 Antenna will stationary if the input signal isAntenna will stationary if the input signal is
0v0v..
When the antenna is approaching theWhen the antenna is approaching the
desired angle or position, the input signaldesired angle or position, the input signal
must approachmust approach 0v0v..
It can be conclude that the control action isIt can be conclude that the control action is
independent of the output.independent of the output.

7. Close Loop SystemClose Loop System
 Example for antenna pointing systemExample for antenna pointing system

8. Close Loop SystemClose Loop System
 From diagram, ifFrom diagram, if θθ00== θθii thenthen VV00 ==VVii so the error signalso the error signal
VVee == VVii –– VV00
= 0V ( the antenna will be stationary )= 0V ( the antenna will be stationary )
 If theIf the VV00 not equalnot equal VVii ,,VVee greater or less thangreater or less than 0V0V, the, the
antenna will rotate clockwise, anticlockwiseantenna will rotate clockwise, anticlockwise
depending on a polarity ofdepending on a polarity of VVee. This means that the. This means that the
antenna will continue rotating untilantenna will continue rotating until VV00 == VVii ..
• In this example, the system automatically correctsIn this example, the system automatically corrects
the output when the system is disturbed. Thisthe output when the system is disturbed. This
system is known as ‘automatic control system’.system is known as ‘automatic control system’.

9. Open Loop Vs Close LoopOpen Loop Vs Close Loop
Open-loop control system Closed-loop control system
AdvantagesAdvantages
 Easier to build.Easier to build.
 Low cost.Low cost.
 Decrease the required power ofDecrease the required power of
a system.a system.
 Stability is not major problemStability is not major problem
AdvantagesAdvantages
 The system response relativelyThe system response relatively
insensitive to externalinsensitive to external
disturbances and internaldisturbances and internal
variations in system parameters,variations in system parameters,
and this make very accurateand this make very accurate
control.control.
DisadvantagesDisadvantages
 Not accurateNot accurate
 Limitations on application.Limitations on application.
 Can only counteract againstCan only counteract against
disturbances, for which it hasdisturbances, for which it has
been designed; otherbeen designed; other
disturbances cannot be removed.disturbances cannot be removed.
DisadvantagesDisadvantages
 Required high power of a systemRequired high power of a system
 High cost and more complexHigh cost and more complex
 Stability problem, which mayStability problem, which may
tend to overcorrect errors thattend to overcorrect errors that
can cause oscillations ofcan cause oscillations of
constantconstant.

10. Feedback and its effectFeedback and its effect
 Feedback system is a system that maintainsFeedback system is a system that maintains
a relationship between the output and somea relationship between the output and some
reference input by comparing them and usingreference input by comparing them and using
the difference as a means of control.the difference as a means of control.
 Feedback is used to reduce the errorFeedback is used to reduce the error
between reference and the system output .between reference and the system output .
 Feedback effect on performanceFeedback effect on performance
characteristic:characteristic:
 StabilityStability
 Overall gainOverall gain
 SensitivitySensitivity
 External disturbancesExternal disturbances

11. Types of Feedback Control SystemTypes of Feedback Control System
 Single input single output (SISO)Single input single output (SISO)
 SISO control system has a single inputSISO control system has a single input rr andand
single outputsingle output yy .
Controller
Desired
output
response,
r e
_
+
Measurement
Plant
b
+

12. Types of Feedback Control SystemTypes of Feedback Control System
 Multivariable input Multivariable outputMultivariable input Multivariable output
(MIMO).(MIMO).
 MIMO system has a more than one input, rMIMO system has a more than one input, r11, r, r22,,
……, r……, rnn , output, y, output, y11, y, y22, ……, y, ……, ynn and feedback signal,and feedback signal,
bb11, b, b22, ……., b, ……., bnn .
. Output /
Controlled
variable, y
Desired
output
response,
r
r1
bn
+
.
.
.
.
.
.
.........
..
r2
rn
y1
y2
yn
b2
+
b1
+

13. Types of Feedback Control SystemTypes of Feedback Control System
 LinearLinear
 Linear feedback control system is idealizedLinear feedback control system is idealized
models fabricated by analyst purely for simplicitymodels fabricated by analyst purely for simplicity
of analysis and design .of analysis and design .
 Linear systems do not exist in practice, since allLinear systems do not exist in practice, since all
physical system is nonlinear to some extentphysical system is nonlinear to some extent .
 Linear system technique normally used for designLinear system technique normally used for design
and analysis purposes.and analysis purposes.

14. Types of Feedback Control SystemTypes of Feedback Control System
 Non-LinearNon-Linear
 In practice nonlinear effect are exist in allIn practice nonlinear effect are exist in all
physical system.physical system.
 An example nonlinear spring characteristic,An example nonlinear spring characteristic,
nonlinear friction force or torque between movingnonlinear friction force or torque between moving
members, and so on.members, and so on.
 Nonlinear system usually difficult to treatNonlinear system usually difficult to treat
mathematically, and there are no general methodsmathematically, and there are no general methods
available for solving a wide class of nonlinearavailable for solving a wide class of nonlinear
system.system.

15. Types of Feedback Control SystemTypes of Feedback Control System
 ContinuousContinuous
 In a continuous control system, the systemIn a continuous control system, the system
variables are function of a continuous time t.variables are function of a continuous time t.
 DiscreteDiscrete
 A discrete time control system involves one orA discrete time control system involves one or
more variable that are known any at discretemore variable that are known any at discrete
intents of time .intents of time .

16. Types of Feedback Control SystemTypes of Feedback Control System
 Time VaryingTime Varying
 When the parameter of a control system isWhen the parameter of a control system is
varying with time the system is called a time-varying with time the system is called a time-
varying systemvarying system .
 Most physical system contains elements that driftMost physical system contains elements that drift
or vary with timeor vary with time .
 Example : the winding resistance of an electricExample : the winding resistance of an electric
motor will vary when the motor is being firstmotor will vary when the motor is being first
excited and its temperature is rising .excited and its temperature is rising .
 Time InvariantTime Invariant
 Time-Invariant system is a system that theTime-Invariant system is a system that the
parameters of a control system are stationaryparameters of a control system are stationary
with respect to time during the operation of thewith respect to time during the operation of the
systemsystem ..