2 lec Eng

Introduction to the Fundamentals of Automatic Control Theory

The operating principle of automatic control systems. General structure of control systems

f

g	Actuators	Object	y
Controller		(Pr

ŷ

Sensors

g – inputs (desired output response)	y – outputs (actual output response)
f – disturbance	ŷ – measured outputs

Examples of Control Systems

Example 1. Automobile Steering Control System

Controller

Desired

course of + - Error signal Driver travel

			Actuator					Object
										Actual
			Steering
								Automobile		course of
			mechanism							travel
			Sensor
	Measurement
			(visual)

The driver uses the difference between the actual and the desired direction of travel to generate a controlled adjustment of steering wheel

Examples of Control Systems

Example 2. Automobile interior cabin temperature control system

	Desired					Controller
				Error signal		On-board
temperature			+ -
set by the						computer
	driver

Measured temperature

	Actuator	Object
	Thermostat and	Automobile	Automobile
	air-conditioning	cabin	cabin
			temperature
	Sensor
	Temperature
	sensor

Many automobiles have thermostatically controlled airconditioning systems for the comfort of the passengers. This is the block diagram of an air-conditioning system where the driver sets the desired interior temperature on a dashboard panel.

Examples of Control Systems

Example 3. An aircraft flight path control system using GPS

Controller

Actuators

Object

Desired

Ailerons,

Error signal

Computer

flight path

+

elevators, rudder,

Aircraft

-

from air

Auto-pilot

engine power

traffic

controllers

Measurement

Measured flight pass

Global Positioning

System (GPS)

Actual flight pass

GPS allows each aircraft to know its position in the airspace landing corridor very precisely. This is the block diagram depicting how an air traffic controller might use GPS for aircraft collision avoidance.

Requirements to Automatic Control Systems

•Stability

•Accuracy

•Performance/Quality

What is Performance/Quality of a System?

	g(t)				y(t)
				System
	Input signal				Output signal
(desired altitude)					(actual altitude)

Classification of automatic control systems

On the basis of Mathematical description

Linear or		Stationary or		Lumped or		Deterministic
				distributed
Non-linear		Non-stationary				or stochastic
				parameters

On the basis of Operating principle

Open-loop		Closed-loop		Combined		Self-tuning
						(self-adapting)
systems		systems		control systems
						systems

Classification of automatic control systems

On the basis of signal types

Continuous		Discrete		Digital
(Analog)		(Discrete-Continuous)

Classification of automatic control systems

On the basis of problems to solve

		Programmed control		Tracking systems
Stabilization problem				(servomechanisms)
		g(t) - predetermined
g(t) = const				g(t) - indeterminate
		function
				function

	e.g. temperature	e.g. radar station
	control in an
	incubator