Speed control of dc motor by fuzzy controller

SPEED CONTROL OF DC MOTOR BY FUZZY CONTROLLER

PREM KUMAR

REG NO – 1611110018

M TECH (PED)

INTRODUCTION

The fuzzy logic, unlike conventional logic

system, is able to model inaccurate or

imprecise models. The fuzzy logic approach

offers a simpler, quicker and more reliable

solution that is clear advantages over

conventional techniques. This paper deals with

speed control of Separately Excited DC Motor

through fuzzy logic Controller.

WHAT IS FUZZY LOGIC CONTROLLERS ?

It’s totally different from other controllers,

fuzzy logic's principle is to think like an

organic creature; human.

A form of knowledge representation suitable

for notions that cannot be defined precisely,

but which depend upon their contexts.

HOW DOES IT WORKS?

In fuzzy logic we define human readable

rules to form the target system. For instance

assume we want to control the room

temperature, first of all we define simple rules:

If the room is hot then cool it down

If the room is normal then don't change temperature

If the room is cold then heat it up

HOW DOES IT WORKS? CONT….

BOOLEAN LOGIC REPRESENTATION

Slow Fast

Speed = 0 Speed = 1

bool speed; get the speed if ( speed == 0) {

// speed is slow} else {

// speed is fast}

FUZZY LOGIC REPRESENTATION

For every problem must represent in terms of fuzzy sets.

Slowest

Fastest

Slow

Fast

[ 0.0 – 0.25 ]

[ 0.25 – 0.50 ]

[ 0.50 – 0.75 ]

[ 0.75 – 1.00 ]

FUZZY SETS

Extension of Classical Sets

Fuzzy set is sets with smooth boundary

Membership function

A fuzzy set defined by the function that

maps objects in a domain of concern to

their membership value in the set. Such a

function is called membership function

FUZZY SET OPERATORS

Union

max (fA(x) , fB(x) ) Intersection

min (fA(x) , fB(x) )

ComplementComplement( fA(x) )

LINGUISTIC VARIABLE

Linguistic variables are the input (or) output

variable of the system. Whose values are in

natural language.

Example:

The room is hot – linguistic value

How much it is hot – linguistic variable

TEMPERATURE CONTROLLER

The problem Change the speed of a heater fan, based upon

the room temperature and humidity. A temperature control system has four

settings Cold, Cool, Warm, and Hot

Humidity can be defined by: Low, Medium, and High

Using this we can define the fuzzy set.

STRUCTURE OF FUZZY LOGIC CONTROLLER

ADC

FUZZIFIER

INFERENCE ENGINE

DEFUZZIFIER

DAC

FUZZIFICATION Conversion of real input to fuzzy set values

PROCEDURE

1. Description of the problem in an acceptable

mathematical form.

2. Definition of the threshold for the variables,

specifically the two extremes of the greatest and least

degree of satisfaction.

Based on the above threshold values a proper

membership function is selected among those available

e.g. linear, piece-wise linear, trapezoidal, parabolic... etc.

INFERENCE ENGINE

Which makes the rules works in response to system inputs.

INFERENCE ENGINE

KNOWLEDGE BASE

USER INTERFACE

INFERENCE ENGINE CONT….

These rules are human readable rules

It is basically uses IF-THEN rules to

manipulate input variables.

Example

IF( some function ) THEN( some

function ).

DEFUZZIFICATION

Changing fuzzy output back into

numerical values for system action

There are two major defuzzification techniques

1.Mean Of Maximum method (MOM)

2.Gravity center defuzzifier (GCD)

DEFUZZIFICATION CONT….

Example

let y = {0.1/2 + 0.8/3 + 1.0/4 + 0.8/5 +0.1/6} using GCD method we have

Y = ( 0.1*2 + 0.8*3 + 1.0*4 + 0.8*5 +0.1*6 )

(0.1+ 0.8+ 1.0+ 0.8 +0.1)Y=4

BLOCK DIAGRAM

DC VOLTAGE SOURCE

DC TO DC CONVERTER

DC MOTOR

FUZZY CONTROLLER

PWM GENERATOR

SYSTEM DESCRIPTION

Motor model :

In this model the armature reaction is

neglected.

The Vf and If are maintained constant. That

is field excited separately

The armature voltage is controlled to get

different speed

SYSTEM DESCRIPTION CONT….

A linear model of a simple DC motor

consists of a mechanical equation and

electrical equation as determined in the

following equations


The dynamic model of the system is

formed using these differential equations


DRIVER CIRCUIT :

Here the DC to DC converter is used to

control the armature voltage of the motor.

The switches in the DC to DC converter

are controlled by PWM inverter.

The PWM which compares the corrected

error(ce) signal generated by the fuzzy

controller and reference signal.


ThyristorDC motor(armature

)

Speed measurement

s

Fuzzy controller

PWM controller

Dc source

Ref signal

FUZZY LOGIC CONTROLLER

In this controller the input is speed and

the output is voltage.The membership function

is figured between error and change in error.

After that using pre defined rule the controller

produces signal this signal is called control

variable.it is given to PWM current controller

THE RULE DATABASE TABLE

ADVANTAGES OVER CONVENTIONAL CONTROL TECHNIQUES

Developing a fuzzy logic controller is cheaper

than developing model based or other

controller with comparable performance.

Fuzzy logic controller are more robust than

PID controllers because they can cover a

much wider range of operating conditions.

Fuzzy logic controller are customizable.

DISADVANTAGES OF FUZZY SYSTEM

It is not useful for programs much larger or

smaller than the historical data.

It requires a lot of data

The estimators must be familiar with the

historically developed programs

CONCLUSION

Thus the fuzzy logic controller is

sensitive to variation of the reference speed

attention. It is also overcome the disadvantage

of the use conventional control sensitiveness

to inertia variation and sensitiveness to

variation of the speed with drive system of dc

motor.

THANK YOU

Education

Speed control of dc motor by fuzzy controller