Control Systems Control Systems

Course Code EE 321Course Code EE 321

Credit Hours (Th-Pr)3-1Credit Hours (Th-Pr)3-1

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Books Mostly ConsultedBooks Mostly Consulted

Feedback Control Systems Phillips and Feedback Control Systems Phillips and HarborHarbor

Automatic Control Systems by D’Azzo.Automatic Control Systems by D’Azzo. Modern Control Theory by Ogata.Modern Control Theory by Ogata. Feedback Control SystemsFeedback Control Systems by Norman by Norman

NiseNise

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Course ObjectivesCourse Objectives::

This course is aimed to build a comprehensive This course is aimed to build a comprehensive foundation in the analysis and design of control foundation in the analysis and design of control systems using classical and modern techniques. systems using classical and modern techniques. Both continuous and discrete-time systems are Both continuous and discrete-time systems are included in the course. The course covers included in the course. The course covers Signal flow graph, State variable approach, Signal flow graph, State variable approach, Root-locus analysis and design, Frequency Root-locus analysis and design, Frequency response analysis and design, Discrete-time response analysis and design, Discrete-time systems of digital control systems. systems of digital control systems.

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Introduction of Control Introduction of Control SystemSystem

A system to guide or manipulate A system to guide or manipulate various elements in order to achieve various elements in order to achieve a prescribed result.a prescribed result.

A Control systemA Control system is a device or set is a device or set of devices to manage, command, of devices to manage, command, direct or regulate the behavior of direct or regulate the behavior of other devices or systems.other devices or systems.

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Motivation for Control Motivation for Control EngineeringEngineering

Feedback control has a long history Feedback control has a long history which began with the early desire of which began with the early desire of humans to harness the materials and humans to harness the materials and forces of nature to their advantage. forces of nature to their advantage. Early examples of control devices Early examples of control devices include clock regulating systems and include clock regulating systems and mechanisms for keeping wind-mills mechanisms for keeping wind-mills pointed into the wind. pointed into the wind.

Modern industrial plants have Modern industrial plants have sophisticated control systems which are sophisticated control systems which are crucial to their successful operation.crucial to their successful operation.

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Motivation for Control Motivation for Control EngineeringEngineering

Improved control is a key enabling Improved control is a key enabling technology underpinning:technology underpinning:

enhanced product quality enhanced product quality waste minimization waste minimization environmental protection environmental protection greater throughput for a given installed capacity greater throughput for a given installed capacity greater yield greater yield deferring costly plant upgrades, and deferring costly plant upgrades, and higher safety marginshigher safety margins

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Kinds of control SystemsKinds of control Systems Control systems are broadly classified as Control systems are broadly classified as

either CLOSED-LOOP or OPEN-LOOPeither CLOSED-LOOP or OPEN-LOOP Systems in which the output quantity Systems in which the output quantity

has no effect upon the process input has no effect upon the process input quantity are called quantity are called open-loop control open-loop control systems.systems.

Systems in which the output has an Systems in which the output has an effect upon the process input quantity in effect upon the process input quantity in such a manner as to maintain the such a manner as to maintain the desired output value are called desired output value are called closed-closed-loop control systems. .loop control systems. .

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Open Loop SystemOpen Loop System

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Closed loop systemClosed loop system

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The block diagrams of the open-loop The block diagrams of the open-loop and the closed-loop temperature control and the closed-loop temperature control systems are shown below,systems are shown below,

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Why Use Feedback Why Use Feedback Control?Control?

                The first question is really "Why do you need a control The first question is really "Why do you need a control system at all?"  Consider the following. system at all?"  Consider the following.

What good is an airplane if you are a pilot and you can't make it What good is an airplane if you are a pilot and you can't make it go where you want it to go? go where you want it to go?

What good is a chemical products production line if you can't What good is a chemical products production line if you can't control temperature, pressure and pH in the process and you control temperature, pressure and pH in the process and you end up making tons of garbage? end up making tons of garbage?

What good is an oven if you can't control the temperature?  What good is an oven if you can't control the temperature?  (And, does it matter if it's an oven in a kitchen or an oven in a (And, does it matter if it's an oven in a kitchen or an oven in a heat-treating department that is used to harden metal parts?) heat-treating department that is used to harden metal parts?)

What good is a pump if you can't control the flow rate it What good is a pump if you can't control the flow rate it produces?  (And, there are many times when the flow rate must produces?  (And, there are many times when the flow rate must be controlled.) be controlled.)

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Other types of control Other types of control systemssystems

Regulatory SystemRegulatory System Servomechanism (follower System)Servomechanism (follower System) SISO SystemSISO System MIMO SystemMIMO System Linear systemLinear system Time Invariant SystemTime Invariant System Time Variant SystemTime Variant System

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Elements of Control Elements of Control SystemSystem

Control theoryControl theory is an interdisciplinary is an interdisciplinary branch of branch of engineeringengineering and and mathematicsmathematics, , that deals with the behavior of that deals with the behavior of dynamical systemsdynamical systems. The desired output . The desired output of a system is called the of a system is called the referencereference. When . When one or more output variables of a system one or more output variables of a system need to follow a certain reference over need to follow a certain reference over time, a time, a controllercontroller manipulates the inputs manipulates the inputs to a system to obtain the desired effect to a system to obtain the desired effect on the output of the system.on the output of the system.

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Elements of Control Elements of Control SystemSystem

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SensorsSensors

Sensors are the Sensors are the eyeseyes of control of control enabling one to enabling one to seesee what is going on. what is going on. Indeed, one statement that is Indeed, one statement that is sometimes made about control is: sometimes made about control is:

If you can measure it, you can control If you can measure it, you can control itit..

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ActuatorsActuators

Once sensors are in place to report on Once sensors are in place to report on the the statestate of a process, then the next of a process, then the next issue is the ability to affect, or issue is the ability to affect, or actuate, the system in order to move actuate, the system in order to move the process from the current state to a the process from the current state to a desired statedesired state

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In summary:In summary:

Sensors provide the eyes and Sensors provide the eyes and actuators the muscle but control actuators the muscle but control

science provides the finesse.science provides the finesse.

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Better ControlProvides more finesse by combining sensors and actuators in more intelligent ways

Better ActuatorsProvide more Muscle

Better SensorsBetter Sensors

Provide better Provide better VisionVision

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Block diagram of closed Block diagram of closed loop control systemloop control system

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Input/ output Input/ output relationshiprelationship Here, we have two elements, the plant with transfer function, G, Here, we have two elements, the plant with transfer function, G,

and feedback transfer function, H. The action of the summing and feedback transfer function, H. The action of the summing junction is to subtract the feedback signal B(s) from the input junction is to subtract the feedback signal B(s) from the input R(s) with the result known as the error signal, E(s) = R(s) - B(s).R(s) with the result known as the error signal, E(s) = R(s) - B(s).

We exploit the properties of Laplace transforms and write the We exploit the properties of Laplace transforms and write the following relationships:following relationships:

C(s) = G(s) E(s)C(s) = G(s) E(s)

E(s) = R(s) - B(s)E(s) = R(s) - B(s)

B(s) = H(s) C(s)B(s) = H(s) C(s)

If we want to know the relationship between the output and the If we want to know the relationship between the output and the input (and who wouldn't?) we eliminate the extra variable. input (and who wouldn't?) we eliminate the extra variable.

C = G E C = G E = G(R-B) = G(R-B) = G(R - HC)= G(R - HC)

C(1+GH) = GRC(1+GH) = GR

C/R = G/(1+GH)C/R = G/(1+GH)