linear control system introduction

Topics: Control theory, Control system, Feedback Pages: 8 (709 words) Published: May 5, 2014
Chapter I
Introduction to control systems

1

EE352: Lecture 01: Introduction to linear control systems

Definition 1 (Control system). an interconnection of subsystems and processes forming a configuration that will lead to the desired output, given a specified input.

Desired output
Reference input

Control system

plant

reference input

Actual output
system response

controlled variable

The control system manipulates the input of the process to get the desired response

2

EE352: Lecture 01: Introduction to linear control systems

I.1
I.1.1

Classification of control systems
regulator-type

The output must be held as close as possible (regulated) to a desired input value (usually constant). Examples

:

• Air conditioning system.
• Car speed regulator
• Oven temperature control
I.1.2

Tracking-type or Servomechanisms

The output must be forced to follow a changing input.
Examples:
• Anti-missiles tracking systems.
• Tele-surgery
• Solar tracking systems

3

EE352: Lecture 01: Introduction to linear control systems

I.2

Control systems configurations

Two main configurations:
I.2.1

Closed loop control systems

(feedback control system) uses the difference between the desired output (reference input) and a feedback of the actual output to control systems.
The systems has a loop (closed loop system)
Desired output
Comparator

Actual output
Controller

Process

Feedback

Examples:
• Air conditioning system: the output is the room temperature. • Car speed regulators: the output is the speed of the car. • Anti locking system (ABS): the output is the locking state of the wheels. 4

EE352: Lecture 01: Introduction to linear control systems

I.2.2

Open-loop control system

The systems is controlled without feedback (without knowing what is the real output). There is no loop, or open-loop.
Desired output

Process

Controller

Examples:
• Washing machines: the output is the degree of cleanness of the clothes. • Air fans: the output is the degree of cooling.
• Toasters: the output is the color of the toast.

5

Actual output

EE352: Lecture 01: Introduction to linear control systems

I.3

Elements of standard feedback control systems

reference input
Input transducer
r(t)

Controller

d(t) Disturbance

Actuator

Process

Actual output
y(t)

The plant
Sensor
• Reference input: desired output of the control system
• The process: the systems whose output is being controlled • The actuator: the system that causes the process to change • The controller: based on the difference between the desired and the actual output. the controller generate the control signal that drives the process to get the desired output. • The plant: refers to the system which combines all the systems between the controller and the process output.

• The sensor: the system that measures the output and converts it to the type (usually electrical) used by the controller . It provides output feedback.
6

EE352: Lecture 01: Introduction to linear control systems

• The input transducer: a system that processes the reference input and converts it to the type (usually electrical) used by the controller .
• The disturbance signal: An external (uncontrollable) signal that disturbs the process away from the desired state (undesirable)
Example 1: Car speed control system
Wind+slope
desired speed

+


throttle control

Engine +

Actual speed
Car body

The plant
speedometer

7

EE352: Lecture 01: Introduction to linear control systems

Example 2: Room heater control
Heat loss
desired temperature
+
− Control

Gas valve

Heater

+ −

The plant
temperature sensor

8

Room temperature
Room

EE352: Lecture 01: Introduction to linear control systems

I.4

The control design process

What are the typical design process steps for a feedback control system? Case study: the antenna azimuth position...
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