Lecture2(introduction)

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Lecture2(introduction)

  1. 1. Introduction to :Introduction to :Control SystemsControl SystemsEngineeringEngineeringLecture #02Lecture #02
  2. 2. Basic ConceptBasic Concept Control system is designed to obtain aControl system is designed to obtain adesired 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 systemfrom 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 controlsystem.system.
  3. 3. Purposes of Control SystemPurposes of Control System Power AmplificationPower AmplificationControl system is used in many systems to produce power gain oramplification. Remote ControlRemote ControlControl system is the key idea for controlling robots and otherautomated systems. Convenience of InputConvenience of InputControl system provides the convenience of input form. For examplewe do not have to put in heat to obtain heat for a temperaturecontrol system. For this case, the input is the position on thethermostat and the output is the heat. Compensation of DisturbanceCompensation of DisturbanceControl system can compensate disturbance. For example, in thecase of an antenna which is positioned in a specific direction, thecontrol system detects any variation in the position due todisturbance like wind and positions the antenna back to the originalposition.
  4. 4. CONTROL SYSTEMCONTROL SYSTEMOPEN LOOPOPEN LOOP CLOSE LOOPCLOSE LOOP The output is notThe output is notmeasured.measured. Control system isControl system isindependent of theindependent of theoutput.output. System cannotSystem cannotcompensate forcompensate fordisturbance.disturbance. Examples : toaster,Examples : toaster,washing machine, fan.washing machine, fan. System has feedback andSystem has feedback andoutput is measuredoutput is measured System output has anSystem output has aneffect on the controleffect on the controlactionaction system can compensatesystem can compensatefor disturbance.for disturbance. Examples :air conditioner,Examples :air conditioner,robot (arm).robot (arm).
  5. 5. Open Loop SystemOpen Loop System Example for antenna pointing systemExample for antenna pointing system
  6. 6. Open Loop SystemOpen Loop System Antenna will rotateAntenna will rotate clockwiseclockwise andandanticlockwiseanticlockwise depending on the outputdepending on the outputsignal,signal, negativenegative oror positive.positive. Antenna will stationary if the input signal isAntenna will stationary if the input signal is0v0v..When the antenna is approaching theWhen the antenna is approaching thedesired angle or position, the input signaldesired angle or position, the input signalmust approachmust approach 0v0v..It can be conclude that the control action isIt can be conclude that the control action isindependent of the output.independent of the output.
  7. 7. Close Loop SystemClose Loop System Example for antenna pointing systemExample for antenna pointing system
  8. 8. Close Loop SystemClose Loop System From diagram, ifFrom diagram, if θθ00== θθii thenthen VV00 ==VVii so the error signalso the error signalVVee == 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, theantenna will rotate clockwise, anticlockwiseantenna will rotate clockwise, anticlockwisedepending on a polarity ofdepending on a polarity of VVee. This means that the. This means that theantenna will continue rotating untilantenna will continue rotating until VV00 == VVii ..• In this example, the system automatically correctsIn this example, the system automatically correctsthe output when the system is disturbed. Thisthe output when the system is disturbed. Thissystem is known as ‘automatic control system’.system is known as ‘automatic control system’.
  9. 9. Open Loop Vs Close LoopOpen Loop Vs Close LoopOpen-loop control system Closed-loop control systemAdvantagesAdvantages Easier to build.Easier to build. Low cost.Low cost. Decrease the required power ofDecrease the required power ofa system.a system. Stability is not major problemStability is not major problemAdvantagesAdvantages The system response relativelyThe system response relativelyinsensitive to externalinsensitive to externaldisturbances and internaldisturbances and internalvariations in system parameters,variations in system parameters,and this make very accurateand this make very accuratecontrol.control.DisadvantagesDisadvantages Not accurateNot accurate Limitations on application.Limitations on application. Can only counteract againstCan only counteract againstdisturbances, for which it hasdisturbances, for which it hasbeen designed; otherbeen designed; otherdisturbances 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 maytend to overcorrect errors thattend to overcorrect errors thatcan cause oscillations ofcan cause oscillations ofconstantconstant.
  10. 10. Feedback and its effectFeedback and its effect Feedback system is a system that maintainsFeedback system is a system that maintainsa relationship between the output and somea relationship between the output and somereference input by comparing them and usingreference input by comparing them and usingthe 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 errorbetween reference and the system output .between reference and the system output . Feedback effect on performanceFeedback effect on performancecharacteristic:characteristic: StabilityStability Overall gainOverall gain SensitivitySensitivity External disturbancesExternal disturbances
  11. 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 andandsingle outputsingle output yy .ControllerDesiredoutputresponse,r e_+MeasurementPlantb+
  12. 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 /Controlledvariable, yDesiredoutputresponse,rr1bn+.................r2rny1y2ynb2+b1+
  13. 13. Types of Feedback Control SystemTypes of Feedback Control System LinearLinear Linear feedback control system is idealizedLinear feedback control system is idealizedmodels fabricated by analyst purely for simplicitymodels fabricated by analyst purely for simplicityof analysis and design .of analysis and design . Linear systems do not exist in practice, since allLinear systems do not exist in practice, since allphysical system is nonlinear to some extentphysical system is nonlinear to some extent . Linear system technique normally used for designLinear system technique normally used for designand analysis purposes.and analysis purposes.
  14. 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 allphysical 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 movingmembers, and so on.members, and so on. Nonlinear system usually difficult to treatNonlinear system usually difficult to treatmathematically, and there are no general methodsmathematically, and there are no general methodsavailable for solving a wide class of nonlinearavailable for solving a wide class of nonlinearsystem.system.
  15. 15. Types of Feedback Control SystemTypes of Feedback Control System ContinuousContinuous In a continuous control system, the systemIn a continuous control system, the systemvariables 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 ormore variable that are known any at discretemore variable that are known any at discreteintents of time .intents of time .
  16. 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 isvarying 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 driftor vary with timeor vary with time . Example : the winding resistance of an electricExample : the winding resistance of an electricmotor will vary when the motor is being firstmotor will vary when the motor is being firstexcited 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 theparameters of a control system are stationaryparameters of a control system are stationarywith respect to time during the operation of thewith respect to time during the operation of thesystemsystem ..

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