IntroductionSystem An interconnection of elements and devices
for a desired purpose.Control System An interconnection of
components forming a system configuration that will provide a
desired response.Process The device, plant, or system under
control.The input and output relationship represents the
cause-and-effect relationship of the
process.Thecontrolsystemisthatmeansbywhichanyquantityofinterestina
machine,mechanismorotherequipmentismaintainedoralteredin accordance
with a desired manner. Consider, for example, the driving system of
an automobile. Speed of the
automobileisafunctionofthepositionofitsaccelerator.Thedesired
speedcanbemaintained(oradesiredchangeinspeedcanbe
achieved)bycontrollingpressureontheacceleratorpedal.This
automobiledrivingsystem(accelerator,carburettorandenginevehicle)
constitutes a control system. Control
SystemIntroductionMultivariable Control ystemOpen-Loop Control
Systems utili!e a controller or control actuator to obtain the
desired response.Closed-Loop Control Systems utili!es feedbac" to
compare the actual output to the desired output response.Open-loop
!An open-loop controller, also called a non-feedback controller, is
a type of controller which computes its input into a system using
only the current state and its model of the system. Diferences!The
terms open-loop control and closed-loop control are often not
clearly distinguished. Therefore, the diference
betweenopen-loopcontrolandclosed-loopcontrolis
demonstratedinthefollowingexampleofaroom
heatingsystem.Inthecaseofopen-loopcontrolofthe
roomtemperatureaccordingtoFiguretheoutdoor temperature will be
measured by a temperature sensor and fed into a control de!ice.
Open-loopOpen-loop!Acharacteristicoftheopen-loopcontrolleristhatit
doesnotusefeedbacktodetermineifitsoutputhas achie!ed the desired
goal of the input. This means that
thesystemdoesnotobser!etheoutputofthe
processesthatitiscontrolling."onse#uently,atrue
open-loopsystemcannotengageinmachinelearning and also cannot
correct any errors that it could make. It
alsomaynotcompensatefordisturbancesinthe system. The
characteristics of feedforward control It has the characteristic of
forward control So, if we use this strategy correctly, the
controlled variable will not deviate set point The advantage of
feedforward control Fig 1-5 Feedforward control TT T team Ti(t)
#eedforward controller SP T(t) Condensation retun The
characteristics of feedforward control !eedforward control cannot
compensate for all disturbances that enter the process The
disadvantage of feedforward control The characteristics of
feedforward control Fig 1-5 Feedforward controlIn this example, The
feedforward control system can compensate only one of disturbances.
If any of the other disturbances enter the process, this strategy
will not compensate for it, and the result will be a permanent
deviation from set point of the controlled variable. The
disadvantage of feedforward control T team Ti(t)f(t) #eedforward
controller SP TT T(t) Condensation retun Closed-loop!
"loseloopcontrolsystemsusetheopen loopsystems$asforwardpath%and
feedbackfromtheoutputtodecidethe inputle!eltotheopenloopsystem.And
because the input is decided based on how
muchawaytheoutputisfromthedesired
le!el,thenonidealitiesinforwardpathdo
notdegradethesystemperformance.The accuracy of the output thus
depends on the feedbackpath,whichingeneralcanbe made !ery accurate.
Closed-loop!In the case of closed-loop control of the room
temperature as shown in Figurethe room temperature is measured and
compared with the set-point !alue. If the room temperature de!iates
from the gi!en set-point !alue, a controller $"% alters the heat
&ow. All changes of the room temperature, e.g. caused by
opening the window or by solar radiation, are detected by the
controller and remo!ed. Closed-loopThe order of e!ents to organise
a closed-loop control is characterised by the following steps'
(easurement of the controlled !ariable"alculation of the control
error $comparison of the controlled !ariable with the set-point
!alue% )rocessing of the control error such that by changing the
manipulated !ariable the control error is reduced or remo!ed The
bloc" diagrams of feedbac" control system!ig #-$ %loc" diagrams of
closed-loop control systems Controller !inal control element
Process or plant SP Output Or Controlled variable Sensor&
Transmitter - Summing 'unction (isturbance )(isturbance # The
advantage of feedbac control1.! "#$T%#& 'T%(T)*I)'"ompensate
for all disturbances The result of any disturbance entering the
process is to mae the controlled variable deviate from the ')T
+#I$T. #nce the controlled variable deviates from the set point,
the controller changes its output to return the controlled variable
to ')T +#I$T,its desired value-.The feedbac control loop does not
now, nor does it care, which disturbance enters the process. It
only tries to maintain the controlled variable at set point, and in
this way compensates for all disturbances. The feedbac controller
wors with minimum nowledge of the process. (ctually, the only
information it needs is in which direction to move, and how much to
move is usually ad.usted by trial and error. The characteristics of
feedbac" control The disadvantage of feedbac control1.! "#$T%#&
'T%(T)*I)'"an compensate for a disturbance only (FT)% the
controlled variable has deviated from the set point because of the
disturbance. "an not give the controlled variable a timely control
The characteristics of feedbac" control T team Ti(t) $rocess fluid
T(t) TT TC SP Condensate return ensor #inal control element
Transmitter Controller Some e*amples+,ashing machineOven-icrowave
oven.ir conditioner!eedforward control system!eedbac" control
system/ow to choose a proper control system00 +!eedbac" control
system1eview+!eedforward control system234 Choose a proper control
system"omparing open-loop control with closed-loop control the
following diferences are seen' Proper Control SystemCan get the
output that a process needLow cost !eedforward Control
System!eedbac" Control SystemCan not compensate all disturbancesCan
compensate all disturbancesimple structure %ow costComple&
structure'igh cost ContrastTrade-off+ Simplicity and low cost
Comple*ity and higher cost ChoiceAn open-loopsystemA
closed-loopsystemPremise+ 5nsure the re6uirement of industrial
productionClosed-loop control !shows a closed-loop action $closed
control loop%* !can counteract against disturbances $negati!e
feedback%* ! can become unstable, i.e.the controlled !ariable does
not fade away, but grows $theoretically% to an in+nite !alue.
Open-loop control !shows an open-loop action $controlled chain%*
!can only counteract against disturbances, for which it has been
designed* other disturbances cannot be remo!ed* ! cannot become
unstable - as long as the controlled ob,ect is stable. -ummarising
these properties we can de+ne' -ystems in which the output #uantity
has no efect upon the process input #uantity are called open-loop
control systems. -ystems in which the output has an efect upon the
process input #uantity in such a manner as to maintain the desired
output !alue are called closed-loop control systems. /istory(att)s
#lyball *overnor+,-th century.*reece +/C. #loat regulator
mechanism'olland +,0th Century. Temperature
regulator/istory(ater-level float regulator/istory/istory#7th
Century 1ames (att)s centrifugal governor for the speed control of
a steam engine.#8)9s Minors"y wor"ed on automatic controllers for
steering ships.#839s 2y3uist developed a method for analy!ing the
stability of controlled systems#8$9s #re3uency response methods
made it possible to design linear closed-loop control systems#8:9s
4oot-locus method due to 5vans was fully developed#8;9s tate space
methods, optimal control, adaptive control and#879s%earning
controls are begun to investigated and developed.Present and
on-going research fields. 4ecent application of modern control
theory includes such non-engineering systems such as biological,
biomedical, economic and socio-economic
systems66666666666666666666666666666666666$a% Automobile steering
control system.$b% The dri!er uses the diference between the actual
and the desired direction of tra!el to generate a controlled
ad,ustment of the steering wheel.$c% Typical direction-of-tra!el
response.5*amples of -odern Control Systems5*amples of -odern
Control Systems5*amples of -odern Control Systems