chapter 1 overview_of_control_system (control systems dae 32103)

DAE 32103 CONTROL SYSTEM 23/02/2014

1

CHAPTER 1OVERVIEW OF

CONTROL SYSTEM© Muhammad Faizal Ismail JKE, PPD, UTHM

Outline:

• Introduction

• Control System Concept

• Type of Control System

• Control System Classification

• Control System Design


2

1.1 INTRO – OBJECTIVE

AfterAfterAfterAfter completingcompletingcompletingcompleting thisthisthisthis chapter,chapter,chapter,chapter,studentstudentstudentstudent willwillwillwill bebebebe ableableableable totototo ::::

• Define the basic features andconfigurations of control systems

• Describe the open/closed-loopcontrol system

• Learn control system applications

• Describe a general process fordesigning a control system

1.2 CONTROL SYSTEM CONCEPT

What is Control System?

• A system that provides anoutput or response for a giveninput

Simplified description of a control system

• Can you give an example?


3

1.2.1 EXAMPLES

aaaa.... Early elevators were

controlled by hand ropes or an

elevator operator. Here, a rope

is cut to demonstrate the

safety brake, an innovation in

early

elevators;

bbbb.... Modern Duo-lift elevators

make their way up the Grande

Arche in Paris, driven by one

motor, with each car

counterbalancing the other.

Today, elevators are fully

automatic, using control

systems to regulate position

and velocity.

ROVER WAS BUILT TO

WORK IN CONTAMINATED

AREAS AT THREE MILE

ISLAND IN MIDDLETON,

PA, WHERE A NUCLEAR

ACCIDENT OCCURRED IN

1979. THE REMOTE

CONTROLLED ROBOT ’S

LONG ARM CAN BE SEEN

AT THE FRONT OF THE

VEHICLE.


4

1.3 WHAT IS SYSTEM?

• Definition: A combination of components or subsystems that act together and perform a certain objectives.

• Systems interact with their environment across a separating boundary.

• The interaction is defined in terms of variables.

– System inputs

– System outputs

– Environmental disturbance


5

1.4 CONTROL SYSTEM COMPONENT

Block

Diagram

Electrical

Hydraulic

Pneumatic

Mechanical

Definition:Definition:Definition:Definition:

An interconnection

of

COMPONENTS

forming a system

configuration

that will provide

a desired system

response

Mathematical

Model

1.5 GENERIC BLOCK DIAGRAM OF CONTROL

SYSTEM

Block

diagrams of

control

systems:

a. open-loop

system;

b. closed-loop

system


6

1.6 TERMS OF BLOCK DIAGRAM

• Input : desired response

• Output : actual response

• Controlled Variable : The quantity or condition that is measured and controlled (normally in the output)

• Manipulated Variable : The quantity or condition that is varied by the controller to adjust the controlled variable.

• Controller : Measuring the controlled variable and applying the manipulated variable to correct deviation of the measured value (output) from a desired value (input).

• Disturbance : Signal that affect the value of the output.

• Plants : Any physical object to be controlled a plant such as a mechanical device, a heating furnace, a chemical reactor or a spacecraft).

• Process : Operation to be controlled . Eg : Chemical , economic and biological process.

• Summing Junction / Feedback Control : to represent addition or subtraction of signals / an operation that, in the presence of disturbances, tends to reduce the difference between output of the system and reference input.


7

1.7 TYPE OF CONTROL SYSTEM

• The control system can be described into

two configuration:

a)a)a)a)OPENOPENOPENOPEN LOOPLOOPLOOPLOOP

b)b)b)b)CLOSEDCLOSEDCLOSEDCLOSED----LOOPLOOPLOOPLOOP

1.7.1 OPEN LOOP CONTROL SYSTEM

• Those systems in which the outputs has no

effect on the control action.

• The output is not compared with the

reference input ( no feedback ).

• Practical example : Washing machine.

Soaking, washing and rinsing in the washer

operate on a time basis. The machine does

not measure the output signal, that is the

cleanliness of the clothes.


8


EXAMPLE

AMPLIFIER

Power

Supply High

power

+V

-V

0V

Input signal

Low

power

MOTOR

GEARS

θO

Output

response


EXAMPLE


9

1.7.3 ADVANTAGE & DISADVANTAGE OF OPEN

LOOP CONTROL SYSTEM

Advantages Disadvantages

1. Stability not a major problem

2. Cheaper than closed loop

system

3. Can be used even if output

cannot be measured

4. Easier to maintain

1. Changes in system or

disturbance cause errors

2. No longer accurate when the

system is disturb. Needs

calibration to maintain

accuracy (Periodic calibration

is required)

3. Low bandwidth – slow

response

1.7.4 CLOSED LOOP CONTROL SYSTEM

• Also known as feedback control system.

• In a closed loop control system the

actuating error signal, which is the

difference between the input signal and the

feedback signal, is fed to the controller so

as to reduce the error and bring the output

of the system to desired value.


10

1.7.5 ADVANTAGE AND DISADVANTAGE OF

CLOSED LOOP CONTROL SYSTEM

Advantages Disadvantages

1. Reduced sensitivity to

disturbances inputs and

parameter changes.

2. Can stabilize an open-loop

unstable plant.

3. Can change system dynamics

speed of response, accuracy,

reduce effects of nonlinearities

4. Highly accurate due to corrective

actions

5. High bandwidth – fast response

1. More complex (Increased

complexity and cost)

2. Risk of instability (stability is

major problem)

1.7.6 CLOSED-LOOP CONTROL SYSTEM

EXAMPLE


11

1.7.6 CLOSED-LOOP CONTROL SYSTEM EXAMPLE


EXAMPLE


12


EXAMPLE

1.7.6 CLOSED-LOOP CONTROL SYSTEM EXAMPLE


13


EXAMPLE


EXAMPLE


14

1.8 FEEDBACK AND ITS EFFECT

• Feedback system is a system that maintains arelationship between the output and somereference input by comparing them and using thedifference as a means of control.

• Feedback is used to reduce the error betweenreference and the system output.

• The feedback has effects on performancecharacteristics as

– Stability

– Overall gain

– Noise (external disturbance).

1.8 FEEDBACK AND ITS EFFECT

Response of a

position control

system

showing effect

of high and low

controller gain

on the output

response


15

• Single input single output (SISO)

• Multiple input multiple output (MIMO)

1.9 CONTROL SYSTEM CLASSIFICATION


• Linear

• Non-linear


16

• Time-variant

- The parameters of this control system donot change with time, e.g. R, L, C.

• Time-invariant

- The parameters of this control systemchange with time. It is difficult to analyze,e.g. resistance winding of a DC motorvaries when the temperature rising, fighteraircraft.


• Analog

- All signals in this system are in the form of analog (continuous) signal.

• Digital (Discrete time)

- A digital computer is used as the controller in the system



17

• Process Control


• Sequential Control– The operations of this control system are

performed in orders which are already setbefore.

– For example in an automatic washing machine,the operations of filling the tube, washing theclothes, draining the tube, rinsing the clothes,and spinning the clothes are already set.



18

1.10 ANALYSIS AND DESIGN

OBJECTIVES

• Three major objectives of systems analysisand design are :

– Producing the desired transient response

– Reducing steady state error

– Achieving stability

1.11 CONTROL SYSTEM DESIGN


19

Summary of today’s lesson?

You have learn:

• The definition of control system.

• The components of control system.

• Block diagram.

• Type of control system.

• How to design a control system.

37

chapter 1 overview_of_control_system (control systems dae 32103)

Engineering

feedback control system

control system applications

openclosedloop control

system configuration

openloop system

closed loop system

control action

output signal