IMPLEMENTATION OF V/F CONTROL OF THREE PHASE INDUCTION MOTOR USING MICROCONTROLLER

7/27/2019 IMPLEMENTATION OF V/F CONTROL OF THREE PHASE INDUCTION MOTOR USING MICROCONTROLLER

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IMPLEMENTATION OF V/F CONTROL OF THREE

PHASE INDUCTION MOTOR USINGMICROCONTROLLER

By

R.BRINDHA(Reg.No: 16104003)

A PROJECT REPORT

Submitted to the Department of

ELECTRICAL AND ELECTRONICS ENGINEERINGin the FACULTY OF ENGINEERING & TECHNOLOGY

In partial fulfillment of the requirementsfor the award of the degree

of

MASTER OF TECHNOLOGY

IN

POWER ELECTRONICS AND DRIVES

S.R.M. ENGINEERING COLLEGES.R.M INSTITUTE OF SCIENCE AND TECHNOLOGY

Deemed Universi ty

June/July, 2006


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BONAFIDE CERTIFICATE

Certified that this project report titled IMPLEMENTATION OF V/F

CONTROL OF THREE PHASE INDUCTION MOTOR USING

MICROCONTROLLER the bonafide work of R.BRINDHA (Reg. No.

16104003) who carried out the research under my supervision. Certified further, that

to the best of my knowledge the work reported here in does not form part of any

other project report or dissertation on the basis of which a degree or award was

conferred on an earlier occasion on this or any other candidate.

Signature of the Guide Signature of the H.O.D

(Ms.N.KALAIARASI, M.E) (Prof.R.CHIDAMBARAM, M.E)

Signature of Internal Examiner Signature of External

Examiner


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ABSTRACT

This project deals with simulation and hardware implementation of scalar

control (V/F control) of three-phase induction motor. The simulation work proves the

concept of V/F control and the software used for simulation is MATLAB

7.0/Simulink package. For simulation the gating pulses of inverter are generated

using Sinusoidal PWM.

The hardware implementation of V/F is also done and proved that the

experimental results are same as that of simulation results. The hardware of V/F

control comprises of three-phase MOSFET inverter, three-phase induction motor and

SPWM pulse generator. Microcontroller is used for generation of Sinusoidal PWM

pulses. It can be used in industrial drive control application.

ACKNOWLEDGEMENT

I would like to express my sincere thanks to

Prof.R.VENKATRAMANI, principal, and Prof.R.MUTHUSUBRAMANIAN

Vice principal for bringing out this project successfully.


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I wish to express my deep sense of gratitude to

Prof.R.CHIDAMBARAM, Head of the department, Department of Electrical and

Electronics Engineering for his permission and encouragement accorded to carry out

this project.

I sincerely thank my project guide Ms.N.KALAIARASI, Lecturer/EEE

who have had an untiring and active participation along the course of my project in

selection of concepts and further development of the project with timely intervention

I wish to give special thanks to my Class-in-charge and project co-

ordinator Mr.S.VENKATESH, Lecturer Department of Electrical and Electronics

for his valuable guidance and continuous encouragement in the course of my work.

I am also grateful to MR.R.CHANDRAMOHAN and all teaching and

non-teaching staff members of the Department of Electrical and Electronics

Engineering for their help during the course of project work. I wish to thank the

management ofS.R.M Institute of Science and Technology (Deemed University)

for their continuous support in my work.

TABLE OF CONTENTS


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CHAPTER NO TITLE PAGE NO

ABSTRACT iiiLIST OF FIGURES vii

LIST OF ABBREVIATIONS viii

1 INTRODUCTION 1

1.1 General 1

1.2 Overview of the Thesis 1

1.3 Objective of The Thesis 2

1.4 Organisation of The Thesis 2

2 INDUCTION MOTOR 3

2.1 Introduction 3

2.2 Basic Operation 3

2.3Speed Torque Characteristics

of Induction Motor 42.4 Summary 6

3 V/F CONTROL METHOD 7

3.1 Introduction 7

3.2 Scalar Control of Induction Motor 7

3.3 V/F Control Theory 9

3.4 Summary 11


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4 SIMULATION OF V/F CONTROL

METHOD 12

4.1 Introduction 12

4.2 V/F Open Loop Control

of Induction Motor 12

4.3 Simulation Results of Open

Loop V/F Control 14

4.4 V/F Closed Loop Control


4.5 Simulation Results of Closed

Loop V/F Control 18

4.6 Summary 19

5 HARDWARE IMPLEMENTATION OF

V/F CONTROL METHOD 20

5.1 Introduction 20

5.2 Implementation for V/F control


5.2.1 Rectifier Unit 21

5.2.2 Pwm-Voltage Source Inverter

Circuit Diagram 21

5.2.3 Microcontroller Circuit Diagram

for Sine Wave Generation 22

5.2.3.1 Power Supply for

Microcontroller 24

5.2.3.2 Algorithm for

Sine Wave Generation 25

5.2.3.3 Flowchart for Sine Wave

Generation 25


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5.2.4 Sinusoidal Pulse Width

Modulation(SPWM) 28

5.2.5 Drive Circuit 30

5.3 Hardware Results of Open Loop V/F

Control of Three-Phase Induction Motor 32

5.3.1 Sinusoidal Waveform 32

5.3.2 Ramp Waveform 33

5.3.3 Comparing Sine with Ramp 33

5.3.4 PWM Pulses Waveform 34

5.3.5 Line Voltage (Vab) Waveform 34

5.4 Summary 35

6 CONCLUSIONS 36

APPENDICES

37

REFERENCES 45


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LIST OF FIGURES

FIGURE DESCRIPTION PAGENO

2.1 Speed Torque Characteristics of Induction Motor 5

3.1 Open Loop Volts/Hertz Control 8

3.2 Speed Torque Characteristics With V/FControl 11

4.1 Open Loop V/F Control Block Diagram 12

4.2 Simulation Diagram of Open Loop V/F Control of

Three-Phase Induction Motor 13

4.3 Output Speed Waveform 14

4.4 Output Gate Pulses 15

4.5 Output Line Voltage Waveform 15

4.6 Closed Loop V/F Control Block Diagram 16

4.7 Simulation Diagram of Closed Loop V/F Control of

Three Phase Induction Motor 17

4.8 Output speed Waveform 18

4.9 Output Line Voltage Waveform 18

5.1 Block Diagram of Hardware Implementation 20

5.2 Rectifier Unit 21

5.3 Circuit Diagram of PWM-Voltage Source

Inverter Circuit Diagram 21

5.4 Hardware Circuit Of Microcontroller for sine wave Generation 23

5.5 Power Circuit Diagram of Microcontroller 24

5.6 Flowchart for Sine Wave Generation 28


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5.7 Circuit Diagram for SPWM Pulse Generation 29

5.8 Circuit Diagram for Ramp Wave Generator 30

5.9 Drive Circuit 30

5.10 Optocoupler 31

5.11 Output Sinusoidal Waveform from Microcontroller 32

5.12 Output Ramp Wave Form 33

5.13 Comparing Sinusoidal Wave With Ramp Wave 33

5.14 PWM Pulses Waveform 34

5.15 Output Voltage Waveform 34

LIST OF ABBREVIATIONS

NO. ABBREVIATIONS DESCRIPTION

1 MOSFET Metal Oxide Field Effect Transistor

2 PWM Pulse Width Modulation

3 ADC Analog to Digital Converter

4 m Actual Speed

5 sl Slip Speed

6 m* Speed Command

7 sl * Slip Speed Command

8 SPWM Sinusoidal Pulse Width Modulation

CHAPTER 1

INTRODUCTION


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1.1GENERAL

Industrial drive applications are generally classified into constant speed and

variable speed drives. Traditionally AC machines have been used in constant speed

applications, whereas DC machines were preferred for variable speed drives. DC

machines have the disadvantages of higher cost and maintenance problems with

commutators and brushes. Commutators and brushes do not permit a machine to

operate in dirty and explosive environment. An AC machine overcomes the draw

back of DC machines. Although currently, the majority of variable speed drive

applications use DC machines, they are progressively being replaced by AC drives.

While there are different methods of speed control of induction motor,

Variable Voltage Variable Frequency (VVVF) or V/F is the most common method of

speed control. This method is most suitable for applications without position control

requirements or the need for high accuracy of speed control. Examples of these

applications include heating, air conditioning, fans and blowers.

1.2OVERVIEW OF THE THESIS

First, implementation of open loop and closed loop V/F control of

induction motor has been done using MATLAB Simulink toolbox and corresponding

waveforms are analyzed.

Finally, hardware implementation for open loop V/F control of three-

phase induction motor is carried out and waveforms are analyzed. A comparison is

made between software implementation and hardware implementation.


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1.3OBJECTIVE OF THE THESIS

To control the speed of three phase induction motor using V/F control

stregery.

1.4ORGANISATION OF THE THESIS

This thesis is organized into five chapters including introduction, brief

description of the thesis and also it deals with the objective and Organisation of the

thesis. Chapter 2 deals with the discussion in detail about basics theory of V/F

control stregery of induction motor. Chapter 3 deals with simulation and results of

V/F control of induction motor. Chapter 4 deals with hardware implementation and

its results of V/F control of induction motor and finally Chapter 5 deals with

conclusion of this project.


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CHAPTER 2

INDUCTION MOTOR

2.1 INTRODUCTION

Induction motors are the most widely used motors in domestic

appliances, industrial control, and automation. Hence they are often called the

workhorse of the motion industry. They are robust, reliable, and durable. When

power is supplied to an induction motor, it runs at its rated speed. However, many

applications need variable speed operations. For example, a washing machine may

use different speeds for each wash cycle. Historically, mechanical gear systems were

used to obtained variable speed. Recently, power electronics and control systems

have matured to allow these components to be used for motor control in place of

mechanical gears.

2.2 BASIC OPERATION

When the rated AC supply is applied to the stator windings, it generates a

magnetic flux of constant magnitude, rotating at synchronous speed. The flux passes

through the air gap, sweeps past the rotor surface and through the stationary rotor

conductors. An electromotive force (EMF) is induced in the rotor conductors due to

the relative speed difference between the rotating flux and stationary conductors.

The frequency of the induced EMF is the same as the supply frequency.

Its magnitude is proportional to the relative velocity between the flux and the

conductors. Since the rotor bars are shorted at the ends, the EMF induced produces a


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current in the rotor conductors. The direction of the rotor current opposes the relative

velocity between rotating flux produced by stator and stationary rotor conductors.

To reduce the relative speed, the rotor starts rotating in the same direction

as that of flux and tries to catch up with the rotating flux. But in practice, the rotor

never succeeds in catching up to the stator field. So, the rotor runs slower than the

speed of the stator field. This difference in speed is called slip speed. This slip speed

depends upon the mechanical load on the motor shaft. The frequency and speed of

the motor, with respect to the input supply, is called the synchronous frequency and

synchronous speed.

Synchronous speed is directly proportional to the ratio of supply

frequency and number of poles in the motor. Synchronous speed of an induction

motor is shown in the equation (2.1)

Where f = rated frequency of the motor

p= number of poles in the motor

Synchronous speed is the speed at which the stator flux rotates. Rotor

flux rotates slower than synchronous speed by the slip speed. This speed is called the

base speed. The speed listed on the motor nameplate is the base speed. Some

manufactures also provide the slip as a percentage of synchronous speed.

2.3 SPEED TORQUE CHARACTERISTICS OF INDUCTION


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MOTOR

The x-axis shows slip speed, the y-axis shows torque and current, the

characteristics shown in Fig 2.1 are drawn with rated voltage and frequency supplied

to the stator. During startup the motor typically draws up to seven times the rated

current. This high current is result losses in the stator and rotor windings, and losses

in the bearings due to the friction.

At startup the motor delivers 1.5 times the rated torque of the motor. This

starting torque is also called locked rotor torque .As the speed increases, the current

drawn by the motor reduces slightly. At the base speed the motor draws the rated

current and delivers the rated torque

At base speed if the load on the motor shaft is increased beyond its rated

torque, the speed starts dropping and slip increases. If the load on the motor is

increased further, it will not be able to take any further load and the motor will stall

In addition when the load is increased beyond

the rated load, the load current increase following the

current characteristics path .Due to this higher

current flow in the windings inherent losses in the

winding increases.

The speed torque characteristic curve is highly non linear as speed varies

in application, the speed needs to be varied which makes the torque vary.


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Fig 2.1 Speed Torque Characteristics of Induction Motor

The disadvantages like motor draws high current during start up, torque

is highly non linear as speed varies. These drawbacks can be overcome by using V/F

control.

2.4 SUMMARY

This chapter describes the principle of operation of induction motor and

its speed torque characteristics. During startup the motor typically draws up to seven

times the rated current. The speed torque characteristic curve is highly non linear as

speed varies. These draw backs can be overcome by using V/F control.


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by controlling the speed of fans, compressors,

pumps, etc.

2) Servo drives: - by means of sophist icated

contro l, induction motors can be used as servo

drives in computer peripherals, machine tools

and robotics.

However by means of power electronic

converters, it is possible to change the speed of an

induction motors. Even though the induction motors

are desirable, their speed control is not as straight

forward as that of a dc motor.

3.2 SCALAR CONTROL OF INDUCTION MOTOR

The following are the scalar control

techniques of an induction motor are given.

(1) Voltage/frequency (V/F) control

(2) Stator current and slip frequency

control

Scalar control, as the name indicates, is due

to magnitude variation of control variables only

and disregards the coupling effect in the machine.


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For example, the voltage of a machine can be

controlled to control the flux, and frequency or slip

can be controlled to control the torque. However,

flux and torque are also the function of frequency

and voltage, respectively.

A simple and popular open loop

voltage/frequency control of induction motor isshown in Fig 3.1 .The power circuit consists of a

phase-controlled rectifier (R) supplied with 3-phase

supply. It is followed by a filter and a PWM inverter

(I). The frequency e*, is the command variable and

it is close to the motor speed. The scheme is

defined as the volts/hertz control because therectifier voltage command, Vs

*, is generated

directly from the frequency signal through a

volts/hertz gain constant (G).


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Fig. 3.1 Open Loop Volt/Hertz Control.

Here, sinusoidal PWM inverter is used because it can provide the

constant volts/hertz supply required for constant-torque operation of an ac motor. An

L-C filter is interposed between the rectifier and the inverter to maintain a ripple free

dc voltage at the input of the inverter, and thus prevent the harmonics in the rectifier

output voltage from getting coupled with the inverter.

3.3 V/F CONTROL THEORY

The base speed of the induction motor is directly proportional to the

supply frequency and the number of poles of the motor. Since the number of poles is

fixed by design, the best way to vary the speed of the induction motor is by varying

the supply frequency. The torque developed by the induction motors is directly

proportional to the ratio of the applied voltage and the frequency of supply. By

varying the voltage and the frequency, but keeping their ratio constant, throughout

the speed range. This exactly what v/f control tries to achieve.


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Other than the variation in speed the torque-speed characteristics of the

V/F control from Fig 3.2 reveals the following.

The starting current requirement is lower.

The stable operating region of the motor is increased. Instead of

simply running at its base rated speed, the motor can be typically from

5% of the synchronous speed up to the base speed .The torque

generated by the motor can be kept constant throughout this region.

At the base speed, the voltage and frequency reach the rated values.

We can drive the motor beyond the base speed by increasing the

frequency further. However, the applied voltage cannot be increased

beyond the rated voltage. Therefore, only the frequency can be

increased, which results in the reduction of torque. Above the speed

the factors governing torque become complex.

The acceleration and deceleration of the motor can be controlled by

controlling the change of the supply frequency to the motor with

respect to time.

The induction motor draws the rated current and delivers the rated torqueat the base speed. When the load is increased, while running at base speed, the speed

drops and slip increases. The motor can take up to 2.5 times rated torque with around

20% drop in speed. Any further increase of load on the shaft can stall the motor.

The torque developed by the motor is directly proportional to the

magnetic field produced by the stator. So the voltage applied to the stator is directly

proportional to the product of the stator flux and angular velocity. This makes the

flux produced by the stator proportional to the ratio of applied voltage and frequency

of supply.

By varying the frequency, the speed of the motor can be varied.

Therefore, by varying the voltage and frequency by the same ratio, flux and hence


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the torque can be kept constant through out the speed range. This makes constant V/F

the most common speed control of the induction motor.

The equations (3.2) and (3.3) shows the

relationship between the voltage and torque versusfrequency. The voltage and frequency being

increased upto the base speed. At the base speed,

the voltage and frequency reach the rated values. We

can drive the motor beyond base speed by increasing

the frequency further. However, the voltage applied

cannot be increased the rated voltage.

Therefore, only the frequency can be

increased, which results in the field weakening and

torque available is being reduced. Above base speed,

the factors governing torque become complex, since

friction and windage losses increase significantly at

highest speeds. Hence, the torque curve becomes

non linear with respect to speed or frequency.


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Fig 3.2 Speed Torque Characteristics With V/F

Control

3.4 SUMMARY

This chapter deals with the V/F control theory and its speed- torque

characteristic states at the base speed, the voltage and frequency reach the rated

values. The motor can be drive beyond the base speed by increasing the frequency.

However, the applied voltage cannot be increased beyond the rated voltage. The

starting current requirement is low. The stable operating region of the motor is

increased.


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CHAPTER 4

SIMULATION OF V/F CONTROL METHOD

4.1 INTRODUCTION

The V/F is simulated on MATLAB/Simulink software. The actual system

can be simulated with a high degree of accuracy in this package. It provides a user

interactive platform and wide variety of numerical algorithm. This Chapter discusses

the realization of V/F control using Simulink block .The Fig (4.2) and (4.8) shows

the basic block Simulink diagram for V/F control of three-phase induction motor.

4.2 V/F OPEN LOOP CONTROL OF INDUCTION MOTOR

The induction motors are often operated in open loop with no velocity or

position feed back.Fig.4.1 shows the open loop v/f control block diagram. The V/F

ratio is maintained constant to provide a constant torque over the operating range.

This form of control is relatively inexpensive and easy to implement.


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Fig.4.1 Open Loop V/F Control Block Diagram

The operation of an ac induction motor is

governed by two principles:

1. Base speed is directly proportional to the frequency of the alternating

current applied to the stator and the number of poles of the motor.

2. Torque is directly proportional to the ratio of applied voltage and

frequency of the applied ac current.

The Fig 4.2 shows the simulation diagram of open loop V/F control of

three-phase induction motor. It consists DC source, three -phase PWM inverter and

three phase induction motor. Dc source is connected to the dc side of the converter.

In this reference speed is set. From that reference speed frequency is determined

using the formulae illustrated in the equation (2.1). V/F function block determines

the amplitude corresponding to that frequency. This frequency and amplitude are

used to update the PWM duty cycle. MOSFET based converter gives the supply of

the induction motor. Connecting the scope through bus selector shows speed of the

induction motor.

Discret

Ts =

v+

-

Vab

Torque

step

Scope

Scope

Mux

Mux2

PWMBLOCKT

m

A

B

C

Induction

g

A

B

C

+

-

Inverter

f(u)

In RM

Discrete

RMS

+

Controlled Voltage

Constant

50

Constan

Cloc


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Fig 4.2 Simulation Diagram of Open Loop V/F Control of Three-Phase

Induction Motor

4.3 SIMULATION RESULTS OF OPEN LOOP V/F CONTROL

The Fig 4.3 shows the simulated speed waveform of open loop V/F

control of three-phase induction motor. Reference speed is set at 1460 RPM. Speed

reaches the steady state at 0.3 second.

Speed

(RPM)

Time (sec)

Fig 4.3 Output Speed Waveform

The Fig 4.4 shows the gate pulses for PWM inverter consists of three

legs, one for each phase. The gating signals for the three phase inverters have a phase

difference of 120. The first pulse is given to the positive switch of phase A, the

pulse is given to the positive switch of phase B the third to the positive switch ofphase C.


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USWA

Time (sec)

USWB

Time (sec)

USWC

Time (sec)

Fig 4.4 Output Gate Pulses

The Fig 4.5 shows the simulated line-to-line voltage waveform of

open loop V/F control of three-phase induction motor. It is observed that the

voltage waveform is almost sinusoidal.


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Voltage(V)

Time (sec)

Fig 4.5 Output Line Voltage Waveform

4.4 V/F CLOSED LOOP CONTROL OF INDUCTION MOTOR

Fig 4.7 shows the block diagram of closed

loop V/F control of three-phase induction motor. The

speed error is processed through a PI controller and

slip speed regulator .The slip speed regulator sets the

slip speed command sl, whose maximum value is

limited to limit the inverter current to a permissiblevalue. The synchronous speed, obtained by adding

actual speed m and slip speed sl, determines the

inverter frequency .The reference signals for the

closed loop control of the machine terminal voltage

Vi* is generated from frequency f using a function

generator .It ensures nearly a constant flux operation

up to the base speed and the operation at a constant

terminal voltage above the base speed.


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A step increased in speed command m*

produces a positive speed error. The slip speed

command sl * is set at a maximum value. The drive

accelerated at a maximum permissible inverter

current, producing the maximum available torque,

unti l the speed error is reduced to a small value.

Fig 4.6 Closed Loop V/F Control Block Diagram

The Fig 4.8 shows the simulation diagram of closed loop V/F control of

three-phase induction motor. It consists DC source, three -phase PWM inverter and

three phase induction motor as open loop in addition to that it has PI controller,

limiter. Connecting the scope through bus selector .Now the simulation circuit is run

with closed loop control shows speed of the induction motor.


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Fig 4.7 Simulation Diagram of Closed Loop V/F Control of Three-Phase

Induction Motor

4.5 SIMULATION RESULTS OF CLOSED LOOP V/F CONTROL

Constant V/HzControl

Discrete,Ts = 3.255e-005 s.

flux

v+

Vab

Scope

Scop

Mux

PWM

BLOCK

MATLA

Functio

MATLAB

Tm

mA

B

CInduction

g

A

B

C

+

-

Inverter

-K-

f(u)

K Ts

z-1

In RMS

Discrete

RMS

DiscretRate

Limite

Discret

Rate

PI

DiscretPI speed

s -

+

Controlled Voltage

Clock

Clock

thet

m


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The Fig 4.9 shows the simulated speed waveform of closed loop V/F

control of three-phase induction motor. Reference speed is set at 1460 RPM. It

reaches the steady state at 0.1 second

Speed (rpm)

Time (sec)

Fig 4.8 Output Speed Waveform

The Fig 4.10 shows the simulated line-to-line voltage waveform of

closed loop V/F control of three-phase induction motor. It is observed that the

voltage waveform is almost sinusoidal

Voltage(V)

Time (sec)

Fig 4.9 Output Line Voltage Waveform

The Fig 4.11 shows the output current waveform of phase A closed loop

V/F control of three-phase induction motor. It is found that the output current

waveform is distorted


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4.6 SUMMARY

This chapter describes the simulation of V/F control of induction motor

using MATLAB/Simulink and simulation results were presented. From the outputs

obtained it is clearly observed that the time taken for speed waveform for closed loop

control reaches the steady state faster than open loop control. It is also observed that

the average output of three-phase line-to-line voltage waveform is almost sinusoidal.


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CHAPTER 5

HARDWARE IMPLEMENTATION OF V/F CONTROL

METHOD

5.1 INTRODUCTION

The V/F control of three-phase induction motor is implemented in

hardware and the gating pulses for the inverter fed motor are generated through the

PIC Microcontroller. The main controlling unit of the project is the microcontroller.

5.2 IMPLEMENTATION FOR V/F CONTROL OF INDUCTION

MOTOR


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Fig 5.2 Rectifier Unit

5.2.2 PWM-Voltage Source Inverter Circuit Diagram

Fig 5.3 Circuit Diagram of PWM-Voltage Source Inverter Circuit Diagram

The Fig 5.3 shows PWM-voltage source inverter circuit diagram.

Inverters are employed to get a variable frequency as supply from a dc supply. For

the control of ac motor, voltage should also be controlled along with frequency.

Variation in output voltage can be achieved by varying the input dc voltage. Output

voltage and current have stepped waveform. Consequently they have substantial

amount of harmonics. Variable frequency and variable voltage ac is directly obtained

from fixed voltage dc when the inverter is controlled by pulse width modulation the

pwm control also reduces harmonics in the output voltage and also it eliminates the

following draw back of 6-step inverter drives like the motor losses increases at all

speeds causing derating of motor, torque pulsation at low speeds.


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In this method, several pulses per half cycle are used as in case of

multiple pulse width modulation. Instead of maintaining the width of all pulses the

same as in the case of multiple pulse modulation, the width of each pulses is varied

proportional to the amplitude of a sine wave evaluated at the center of the same

pulses. By comparing a sinusoidal reference signal with a triangular carrier wave

frequency, fc, the gating signal are generated.

The PWM control has the following advantages,

(1)The output voltage control can be obtained with out any additional components

(2)With this type of control, lower order harmonics can be eliminated of minimized

along with its output voltage control. The filtering requirements are minimized

as higher order harmonics can be filtered easily

5.2.3 Microcontroller Circuit Diagram for Sine Wave Generation

The PIC microcontroller is the main controlling unit of the project. The

main features and sine wave generation of PIC microcontroller (16F877A) is

explained section 5.3.3.a. Fig 5.5 shows the pin diagram of microcontroller, Digital

to Analog (DAC) and Buffer. Microcontroller used is a 40 pin single chip IC. It has 5

ports, they are A, B, C, D and E. It has 3 Digital to Analog Converters (DAC) and 5

latches RAX, RBX, RCX, and RDX AND REX.


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Fig 5.4 Hardware Circuit of Microcontroller for Sine Wave Generation


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Design Features of Microcontroller

1. Input to DAC through PORT C

2. RB0 FIRST LATCH CONTROL BIT

3. RB1- SECOND LATCH CONTROL BIT

4. RB2- THIRD LATCH CONTROL BIT

5. Give the array a[ ] element to PORT C and enable first latch by setting

RB0.by doing this R phase DAC produced its waveform. Give small delay in

between switching two latches. Enable second latch by setting RB1 and give

b[ ] input to DAC2.similarlygive input to DAC 3.

6. After giving to 3 DAC give a delay that will determine the frequency. This

delay is obtained from the DAC

5.2.3.1. Power Supply for Microcontroller

All electronic circuits works only in low DC voltage, so we need a power

supply unit to provide the appropriate voltage supply for their proper functioning. Fig 5.6

shows the power circuit diagram of microcontroller. This unit consists of transformer,

rectifier, filter & regulator. AC voltage of typically 230v rms is connected to a

transformer voltage down to the level to the desired ac voltage. A diode rectifier that

provides the full wave rectified voltage that is initially filtered by a simple capacitor

filter to produce a dc voltage. This resulting dc voltage usually has some ripple or ac

voltage variation. A regulator circuit can use this dc input to provide dc voltage that not

only has much less ripple voltage but also remains the same dc value even the dc voltage

varies somewhat, for the load connected to the output dc voltages changes.


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Fig 5.5 Power Circuit Diagram of Microcontroller

5.2.3.2 Algorithm for Sine Wave Generation

Calculate the array elements using the formula 128+ 128sin(alpha),

128+128sin (120+alpha), 128+ 128sin(240+alpha) Array name a [], b [], c []

Initialize PORTC, PORT B as output port and port RA0 as input port, ADC

Module

Turn on ADC

Wait till completion of conversion.

Give phase A data to PORTC

Turn on the phase A latch by setting RB0. Give phase B data to PORT C

Turn on phase B latch by setting RB1

Give phase C data to port C

Turn on phase C latch by setting RB2

Give a long delay. That delay period obtained from ADC which determines

frequency (if ADC value Z=0 the frequency=12 hertz

If ADC value Z=255 the frequency=50 hertz

Until the first half cycle is reached, Repeat the above steps from step 4

Subtract the array element from 255 and give to ADC.for producing negative

half cycle

5.2.3.3 Flowchart for Sine Wave Generation


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The main logic for sine wave generation using microcontroller is

explained in the flow chart Fig 5.6

Start

Initialize

Ports And ADC

Convert ADC Results Into A Byte

and Store It In Available Z

Load 2 Micro

Second Delay

Set RB0 [Turn On

Phase A Latch]

Clear RB0 [Shunt Off Phase A Latch]

D

B

Load Phase B Input To Port C

[Input Stored In Array B [ ] ]

Load Phase A Input To Port C

[Input Stored In Array A [ ] ]


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NO

Clear RB1 [Shunt Off

Phase B Latch]

Set RB2 [Turn On

Phase C Latch]

Clear RB2 [Shunt Off

Phase C Latch]

Increment I register

IF

i < 90

Load 2 Micro

Second Delay Period

Load Delay

Period Of Z+75

Milli Second

B

Load 2 Micro Second

Delay Period To ADC

Set RB0 [TurnOn Phase A

Load Phase C Input To Port C

[Input Stored In Array C[ ] ]


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YES

NO

YES

Fig 5.6 Flowchart for Generating Sine Wave

5.2.4. Sinusoidal Pulse Width Modulation (SPWM)

Fig 5.8 shows the SPWM pulse generation circuit diagram. This circuit

generates sinusoidal pwm pulse. The output wave of Microcontroller is given as the

PORT C = 255-a[i]

= 255-b[i]

= 255-c[i]

Set Port B

Load 2 Micro

Second Delay

Period To ADC

Clear Port BLoad Delay Period Z+75

Milli Second To A

Initialize K

Increment K register

IF

K< 90

Stop

D


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input to pin 3 of LM324 the circuit. The output got from the pin 1of (LM324) buffer

in similar to that the input, which is then fed through a pin 5 of square wave

converter (LM358) to produce square wave. When the sine wave is passed through

precisition rectifier (LM38), it produces rectified output. This rectified output from

pin 7 and the ramp wave generated from pin 5 of the Ramp generators (ICL8038) are

compared and produces PWM pulses of the cycle at pin 7.

Some of the square wave when passed through a transistor is converted

into an inverted square wave. The inverted square wave is fed through a AND gate

(CD4053) and the output got is also in the form of inverted square wave with delay

time, this delay is due to the diode present in the AND gate.

Some of the square wave directly fed to AND gate and produce square

wave of the cycle with delay time due to diode action.

Two types of results were produced while comparing with PWM pulses.

When the PWM pulses compared with the positive cycle square wave it produces the

positive cycle PWM pulses.

When the PWM pulses compared with the negative cycle square wave it

produces the negative cycle PWM pulses.


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Fig5.7 Circuit Diagram for SPWM Pulse Generation


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Fig5.8 Circuit Diagram for Ramp Wave Generator

5.2.5DRIVE CIRCUIT

Drive circuit isolates power circuit (VSI) and microcontroller circuit. The

main function of Drive circuit is isolation and amplification. The Fig 5.9 shows the

drivecircuit


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Fig 5.9 Drive circuit

The output of microcontroller is given to the Buffer IC (CD 4050). The

signal is amplified and is given to optocoupler (MCT2E) circuit.

There are many situations where signals and data need to be transferred

from one subsystem to another, without making direct ohmic electrical

connection because the source and destination are at different voltages levels that

is a microcontroller which is operating with 5v dc but being used to control a

MOSFET which is switching 240v AC supply.

An Optocoupler contains a light emitting diode with a light sensitive

device in package. One of the simplest example is LED packed with a

phototransistor. The LED is illuminated by an input supply and the

phototransistor, responding to light, drives an output circuit. Thus the input and

output circuits are coupled by light energy alone. The principal advantage of this

arrangement is excellent electrical isolation is between input and output. These

devices are often called optoisolators. One of the optocoupler is shown in Fig5.10

x

y

a

b

Fig 5.10 Optocoupler

The amplified signal from buffer circuit is fed to the optocoupler. When

the optocoupler input signal is in high state, the optocoupler is activated. When

optocoupler is activated the transistor T1 is activated through resistor (R3). When T1

is activated, the current flows through the supply-D-T1and supply. Due to the


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voltage drop across resistor (R4) the transistor T2 and T3 are activated .Now the

current flows through the D-T2-T3-R7_supply.the pulse is taken across R8.

5.3 HARDWARE RESULTS OF OPEN LOOP V/F CONTROL OF

THREE-PHASE INDUCTION MOTOR

The open loop V/F control of three-phase induction motor is implemented

in hardware and the obtained results are shown below

5.3.1 sinusoidal Waveform

Fig 5.10 shows the sine waveforms obtained from microcontroller and its

frequency is 50 HZ with 120-phase shift. The amplitude of sine wave of phase A

obtained from microcontroller is 2.5V.

Voltage

(V)

Time (millisecond)

Voltage

(V)


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Time (millisecond)

Fig 5.11 Output Sinusoidal Waveform from Microcontroller

5.3.2 Ramp Waveform

The fig 5.12 shows the ramp wave generated from ramp wave generator

(ICL8038) and its frequency is 555 HZ. The amplitude of ramp wave obtained from

PWM generator is 0.7V

Voltage

(V)

Time (millisecond)

Fig 5.12 Output Ramp Wave Form

5.3.3 Comparing Sine with Ramp

The fig 5.13 shows the comparison of sinusoidal wave and ramp wave

for sinusoidal pulse width modulation pulse generation. Modulation index is 1

Voltage

(V)


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Time (millisecond)

Fig 5.13 Comparing sinusoidal Wave With Ramp Wave

5.3.4 PWM Pulses Waveform

The Fig 5.13 shows the pwm pulses obtained by comparing carrier and

sine waveform.

Voltage

(Volts)

time (m sec)

Fig 5.14 PWM Pulses Waveform

5.3.5 Line Voltage (Vab) Waveform

The Fig 5.1.6 shows the voltage waveform for Line-to- Line voltage Vab.

The voltage is obtained from the inverter output terminals is 43V


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CHAPTER 6

CONCLUSIONS

The speed of three-phase induction motor is

being controlled by varying supply voltage and

frequency wi th constant (V/F) ratio. It is simple,

economic to easier to design and implement in open

loop. But the drawbacks of open loop is it doesnt

correct the change in output also it doesnt reach the

steady state quickly.


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These drawbacks can be overcome by modifying an open loop into a

closed loop system. In this project only open loop was implemented in hardware.

The project can be extended in future to control the speed of induction motor in

closed loop.

APPENDICES

//16F870.h Header File/////////Standard Header files for the PIC16F870 device////////

#device PIC16F870

#no list

////////// Program memory: 2048x14 Data Ram: 128 stack: 8

//////////I/O:22 Analog pins: 5

////////// Data EEprom: 1024

////////// C Scratch area: 20 ID locations: 2000


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/////////// Fuses: LP,

XT,HS,RC,NOWDT,WDT,NOPUT,PUT,PROTECT,NOPROTECT,DEBUG////////// Fuses:

NODEBUG, NOBROWNOUT, BROWNOUT, LVP, NOLVP, CPD, NOCPD,

WRT, NOWRT

////////////////////////////////////////////////////////////I/O

// Discrete I/O functions: SET_TRIS_X (), OUTPUT_X (), INPUT_X ()

/// PORT_B_PULLUPS (), INPUT (),

/// OUTPUT_LOW (), OUTPUT_HIGH ()

// OUTPUT_FLOAT (), OUTPUT_BIT ()

//CONSTANTS USED TO IDENTIFY PINS IN THE ABOVE ARE:

#define PIN_A0 40

#define PIN_A1 41#define PIN_A2 42

#define PIN_A3 43

#define PIN_A4 44

#define PIN_A5 45

#define PIN_B0 48

#define PIN_B1 49

#define PIN_B2 50

#define PIN_B3 51

#define PIN_B4 52

#define PIN_B5 53

#define PIN_B6 54

#define PIN_B7 55

#define PIN_C0 56

#define PIN_C1 57

#define PIN_C2 58

#define PIN_C3 59

#define PIN_C4 60

#define PIN_C5 61

#define PIN_C6 62

#define PIN_C7 63

////////////////////////////////////////////////////////////

Useful defines

#define FALSE 0

#define TRUE 1

#define BYTE int

#define BOOLEAN short int


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#define getc getch#define fgetc getch

#define getcahr getch

#define putc putchar

#define fputc put char

#define fgets gets

#define fputs puts

/////////////////////////////////////////////////////////////

control

// control function: RESET_CPU (), SLEEP (), RESTART_CAUSE ()

// CONSTANTS RETURNED FROM RESTART_CAUSE () ARE:

#define WDT_FROM_SLEEP 0

#define WDT_TIMEOUT 8

#define MCLR_FROM_SLEEP 16

#define NORMAL_POWER_UP 24

//////////////////////////////////////////////////////////

Timer 0

// Timer 0 (AKA RTCC) functions: SETUP_COUNTERS () OR SETUP_TIMER0 ()

// SET_TIMER0() OR SET_RTCC(),

// GET_TIMER0() OR GET_RTCC()

// CONSTANTS USED FOR SETUP_TIMER0() are:

#define RTCC_INTERNAL 0

#define RTCC_EXT_L_TO_H 32

#define RTCC_EXT_H_TO_L 48

#define RTCC_DIV_1 8







#define RTCC_DIV_128 6#define RTCC_DIV_256 7

#define RTCC_8_BIT 0

// constants used for SETUP_COUNTERS() are the above

// constants for the 1st param and the following for

// the 2nd param:


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//////////////////////////////////////////////////////////////// WDT// watch Dog Timer Functions: SETUP_WDT() or SETUP_COUNTERS() (see

Above)

// RESTART_WDT ()

//

#define WDT_18MS 8

#define WDT_36MS 9

#define WDT_72MS 10

#define WDT_144MS 11





//////////////////////////////////////////////////////////////

TIMER 1

// Timer 1 Function: SETUP_TIMER_1, GET_TIMER1, SET_TIMER1

// constants used for SETUP_TIMER_1 () are:

// (OR (via 1) together constants from each group)

#define T1_DISABLE 0

#define T1_INTERNAL 0X85

#define T1_EXTERNAL 0X87

#define T1_EXTERNAL_SYNC 0X83

#define T1_CLK_OUT 8

#define T1_DIV_BY_1 0

#define T1_DIV_BY_2 0X10



////////////////////////////////////////////////////////////

TIMER 2

// Timer 2 Function : SETUP_TIMER_2,GET_TIMER2, SET_TIMER2constants used for SETUP_TIMER_2() are:

#define T2_DISABLE 0




//////////////////////////////////////////////////////////CCP


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//CCP Functions :SETUP_CCPX,SET_PWMX_DUTY

//CCP Variables :CCP_X,CCP_X_LOW,CCP_X_HIGH//constants used for SETUP_CCPX() are:

#define CCP_OFF 0

#define CCP_CAPTURE_FE 4

#define CCP_CAPTURE_RE 5

#define CCP_CAPTURE_DIV_4 6

#define CCP_CAPTURE_DIV_16 7

#define CCP_COMPARE_SET_ON_MATCH 8

#define CCP_COMPARE_CLR_ON_MATCH 9

#define CCP_COMPARE_INT 0XA

#define CCP_COMPARE_RESET_TIMER 0XB

#define CCP_PWM 0XC

#define CCP_PWM_PLUS_1 0XIC#define CCP_PWM_PLUS_2 0X2C

#define CCP_PWM_PLUS_3 0X3C

long CCP_1;

#byte ccp_1 = 0X15

#byte ccp_1_LOW= 0X15

#byte ccp_1_HIGH= 0X16

/////////////////////////////////////////////////////////// PSP

// PSP FUNCTIONS: SETUP_PSP, PSP_INPUT_FULL(), PSP_OUTPUT_FULL(),

// PSP_OVERFLOW(), INPUT_D(),OUTPUT_D()

// PSP VARIABLES: PSP_DATA

//Constants used in SETUP_PSP() are:

#define PSP_ENABLED 0X10

#define PSP_DISABLED 0

#byte PSP_DATA= 8

/////////////////////////////////////////////////////SPI

//SPI Functions:SETUP_SPI,SPI_WRITE,SPI_READ, SPI_DATA_IN

//Constants used in SETUP_SSP() ARE:

#define SPI_MASTER 0X20#define SPI_SLAVE 0X24

#define SPI_L_TO_H 0

#define SPI_H_TO_L 0X10

#define SPI_CLK_DIV_4 0



#define SPI_CLK_T2 3


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#define SPI_SS_DISABLED 1

///////////////////////////////////////////////////// ADC

//ADC FUNCTIONS:SETUP_ADC() ,SETUP_ADC_PORTS() (aka

SETUP_PORT_A),

// SET_ADC_CHANNAL(),READ_ADC()

//Constants used in SETUP_ADC_PORTS() are:

#define NO_ANALOGS 0X86 //NONE

#define ALL_ANALOG 0X80 //A0 A1 A2 A3 A5 E0 E1 E2

Ref=Vdd

#define A_ANALOG_RA3_REF 0X81 //A0 A1 A2 A5 E0 E1 E2

Ref=A3

#define A_ANALOG 0X82 //A0 A1 A2 A3 A5 Ref=Vdd

#define A_ANALOG_RA3_REF 0X83 // A0 A1 A2 A5 Ref=A3#define RA0_RA1_RA3_ANALOG 0X84 //A0 A1 A3 Ref=Vdd

#define RA0_RA1_ANALOG_RA3_REF 0X85 //A0 A1 Ref=A3

#define ANALOG_RA3_RA2_REF 0X88 //A0 A1 A5 E0 E1 E2

Ref=A2,A3

#define ANALOG_NOT_RE1_RE2 0X89 //A0 A1 A2 A3 A5 E0

Ref=Vdd

#define ANALOG_NOT_RE1_RE2_REF_RA3 0X8A //A0 A1 A2 A5 E0

Ref=A3

#define ANALOG_NOT_RE1_RE2_REF_RA3_RA2 0X8B //A0 A1 A5 E0

Ref=A2,A3

#define A_ANALOG_RA3_RA2_REF 0X8C //A0 A1 A5 Ref=A2,A3

#define RA0_RA1_ANALOG_RA3_RA2_REF 0X8D //A0 A1 Ref=A2,A3

#define RA0_ANALOG 0X8E //A0

#define RA0_ANALOG_RA3_RA2_REF 0X8F //A0 Ref=A2,A3

//CONSTANTS USED FOR SETUP_ADC() ARE:

#Define ADC_OFF 0 //ADC OFF

#Define ADC_CLOCK_DIV_2 1

#Define ADC_CLOCK_DIV_8 0X41

#Define ADC_CLOCK_DIV_32 0X81

#Define ADC_CLOCK_INTERNAL 0Xcl //INTERNAL 2-BUS

// constants used in READ_ADC() are:

#define ADC_STRAT_AND_READ 7 //This is the default if nothing is

specified

#define ADC_START_ONLY 1

#define ADC_READ_ONLY 6


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///////////////////////////////////////////////////////////INT

// interrupt functuion : ENABLE_INTERRUPTS(), DISABLED_INTERRUPTS(),// EXT_INT_EDGE()

//

//Constants used in EXT_INT_EDGE() ARE:

#define L_TO_H 0X40

#define H_TO_L 0

// constants used in ENABLE/DISABLE_INTERRUPTS() are:

#define GLOBAL 0X0BC0

#define INT_RTCC 0X0B20

#define INT_RB 0X0B08

#define INT_EXT 0X0B10

#define INT_AD 0X8C40

#define INT_TBE 0X8C10#define INT_RDA 0X8C20

#define INT_TIMER1 0X8C01

#define INT_TIMER2 0X8C02

#define INT_CCP1 0X8C04

#define INT_SSP 0X8C08

#define INT_PSP 0X8C80

#define INT_BUSCOL 0X8D08

#define INT_EEPROM 0X8D10

#define INT_TIMER0 0X0B20

#list

// 3 phase sinewave generation

#include

#Byte TRISA= 0X85

#Byte TRISB= 0X86

#Byte TRISC= 0X87

#Byte TRISD= 0X88

#byte ADCON0=0X1f

#byte ADCON1=0X9f

#byte ADRESH=0X1e

#byte ADRESL=0X9e#bit ADCGO=0X1f.2

#bit ADON=0X1f.0

#BYTE PORTD=0X08

#BYTE PORTC=0X07

#BYTE PORTB=0X06

#BYTE PORTA=0X05

#fuses HS,NOWDT,NOPROTECT


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#use delay(clock=6000000)

//#org 0x700,0x720int8 i,k,x;

int32 z;

BYTE const a[90]=

{128,132,137,141,146,150,154,159,163,167,171,176,

180,184,188,192,195,199,203,206,210,213,216,219,222,

225,228,231,233,236,238,240,242,244,246,247,249,250,

251,252,253,254,254,255,255,255,255,255,254,254,253,

252,251,250,249,247,246,244,242,240,238,236,233,231,

228,225,222,219,216,213,210,206,203,199,195,192,188,

184,180,176,171,167,163,159,154,150,146,141,137,132};

BYTE CONST b[90]

{238,236,233,231,228,225,222,219,216,213,210,206,203,

199,195,192,188,184,180,176,171,167,163,159,154,150,

146,141,137,132,128,124,119,115,110,106,

102,97,93,89,85,80,76,72,68,65,61,57,53,50,

46,43,40,37,34,31,28,25,23,20,18,16,14,12,10,

9,7,6,5,4,3,2,2,1,1,1,1,1,2,2,3,4,5,6,7,9,10,12,14,16};

BYTE CONST c[90]

{18,16,14,12,10,9,7,6,5,4,3,2,2,1,1,1,1,1,2,2,3,4,5,6,7,

9,10,12,14,16,18,20,23,25,28,31,34,37,40,43,46,50,53,57,

61,64,68,72,76,80,85,89,93,97,102,106,110,115,119,124,128,

132,137,141,146,150,154,159,163,167,171,176,180,184,188,192,

195,199,203,206,210,213,216,219,222,225,228,231,233,236}

void main()

{

do

{

TRISB=0x00;

TRISC=0x00;

TRISA=0x01;

ADCON0=0x81; //ADC MODE=fosc/32,i/p=A0ADCON1=0x8e;

ADCGO=0x01; //READ THE ADC INPUT

while(ADCGO);

z=make16(ADRESH,ADRESL); //PUT THE RESULT IN VARIABLE Z

z=z/4; //SCALE Z VALUE

i=0;


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do

{if (i


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Delay_us(Z);

Delay_us(Z/2);}

}while(++k

Documents

IMPLEMENTATION OF V/F CONTROL OF THREE PHASE INDUCTION MOTOR USING MICROCONTROLLER