SOFT START OF AN INDUCTION MOTOR

USING DSPACE

A Project report submitted in partial fulfilment

of the requirements for the degree of B. Tech in Electrical Engineering

By

Bikram Chowdhury (EE2014/063)

Arghyadeep Patra (EE2014/058)

Archis Rudra (EE2014/062)

Mainak Dutta (EE2015/L01)

Under the supervision of

Dr. Shilpi Bhattacharya

Associate Professor
Dept. of the Electrical Engineering

Department of Electrical Engineering

RCC INSTITUTE OF INFORMATION TECHNOLOGY
CANAL SOUTH ROAD, BELIAGHATA, KOLKATA – 700015, WES T BENGAL
Maulana Abul Kalam Azad University of Technology (MAKAUT)
©2018

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 ACKNOWLEDGEMENT

It is my great fortune that we have got opportunity to carry out this project work under the
supervision of Dr. Shilpi Bhattacharya in the Department of Electrical Engineering, RCC
Institute of Information Technology (RCCIIT), Canal South Road, Beliaghata, Kolkata-
700015, affiliated to Maulana Abul Kalam Azad University of Technology (MAKAUT),
West Bengal, India. we express my sincere thanks and deepest sense of gratitude to my guide
for his constant support, unparalleled guidance and limitless encouragement.

We wish to convey my gratitude to Prof. (Dr.) Alok Kole, HOD, Department of

Electrical Engineering, RCCIIT and to the authority of RCCIIT for providing all kinds of
infrastructural facility towards the research work.

We would also like to convey my gratitude to all the faculty members and staffs of the
Department of Electrical Engineering, RCCIIT for their whole hearted cooperation to make
this work turn into reality.

We would also like to thank FINANCIAL DEPARTMENT, RCCIIT for financial support
to perform this project work.

----------------------------------------------
Signature of Student

Place:

Date:

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 CERTIFICATE

To whom it may concern

This is to certify that the project work entitled Soft Start of an Induction Motor is the bona
fide work carried out by,
Archis Rudra (EE2014/062),
Arghyadeep Patra (EE2014/058),
Bikram Chowdhury (EE2014/063),
Mainak Dutta (EE2015/L01),
students of B. Tech in the Dept. of Electrical Engineering, RCC institute of Information
Technology (RCCIIT), Canal South Road, Beliaghata, Kolkata-700015, affiliated to Maulana
Abul Kalam Azad University of Technology (MAKAUT), West Bengal, India, during the
academic year 2017-18, in partial fulfillment of the requirements for the degree of Bachelor
Of Technology in Electrical Engineering and that this project has not submitted previously
for the award of any other degree, diploma and fellowship.

____________________ ___________________
Signature of the Guide Signature of the HOD
Dr. Shilpi Bhattacharya Alok Koley
Designation : Associate Professor Professor & HOD

______________________________
Signature of the External Examiner
Name:______________________________

Designation:____________________________

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 TABLE OF CONTENTS

Content Page no.

List of Figures 4
Abstract 6
1. Introduction 7
1.1 Background 7
1.2 Problem Statement 8
1.3 Problem Objective 8
2. Theory 9
2.1 Starting 9
2.2 STAR VOLTAGE CONTROL METHOD of Induction motor 10
2.3 Soft starter 12
2.4 Induction Motor 12
2.5 dSPACE 13
2.6 MATLAB and Simulink 16
3. Software Implementation 17
3.1 Zcd and delayed output waveform 18
3.2 Main Simulation diagram 19
3.3 dSpace Control Desk 20
4. Hardware Implementation 21
4.1 Block Diagram 21
4.2 Circuit Diagram 21
4.3 Circuit Description 22
4.4 Hardware Model 22
4.5 Full setup of Final Testing 23
4.5 List of Hardware Component 24
4.6 Main Hardware Component Used 25
4.7 Observation and results 26
5. Conclusion 28
6. Future aspect of the project 28
7. Appendix A 29
8. References 46

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 List of Figures
Fig.1: Speed-Torque characteristics with variable stator voltage

Fig.2: Stator voltage control by semiconductor voltage controller

Fig.3: Cutaway view through stator of the Induction Motor

Fig. 4: CONTROLLER BOARD OF DS1202

Fig.5: Dspace Micro Lab Box Toolkit

Fig.6: Waveform of ZCD and delayed output

Fig.7: ZCD and delayed output waveform using MATLAB

Fig.8: Simulink Circuit Diagram (ZCD along with triggering circuit)

Fig.9: 1200 firing angle

Fig.10: 900 firing angle

Fig.11: 450 firing angle

Fig.12: 00 firing angle

Fig.13: dSpace Control Desk

Fig.14: Block Diagram of Soft starter of an Induction Motor

Fig.15: Circuit Diagram of Soft starter of an Induction Motor

Fig:16 : LIST OF HARDWARE COMPONENT

Fig.17: Full hardware circuit board along with 6v transformer

Fig.18: Final Testing

Fig.19: Real time Simulation

Fig. 20: Pin Description of MOC3021

Fig.21 Pin Description of TRIAC BT-136

Fig.22 Pin Description of BC-547 Fig. 23: Working of Transformer

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 ABSTRACT

The project is designed to provide a soft and smooth start to the induction motor. An
induction motor during the initial starting condition draws up much higher current than its
capacity and the motor instantly reaches the full speed. This results in a mechanical jerk and
high electrical stress on the windings of the motor. Sometimes the windings may get burnt.
The induction motor should start smoothly and gradually catch up the speed for a safer
operation. This project is designed to give a soft start to the induction motor based on the
TRIAC firing triggered by heavily delayed firing angle during starting and then gradually
reducing the delay till it reaches zero voltage triggering. This results in low voltage during
start and then gradually to full voltage. Thus the motor starts slowly and then slowly picks up
to full speed. The control circuit is developed in MATLAB Simulink and Dspace is used as
the control platform. This project consists of one TRIAC in the power circuit, one
TRANSISTOR in the driving circuit, Opto-coupler for bridging the circuit, and the output of
which is connected to a lamp representing the coil of the induction motor.
When the supply is given to the circuit resulting in delayed firing pulses during start and then
gradually reducing the delay till the motor runs at full speed. The Output is fed through opto-
coupler to trigger the TRIAC.

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1. INTRODUCTION :

1.1 BACKGROUND :

Necessity for Motor Protection :

It could be assumed that properly planned, dimensioned, installed, operated and maintained
drives should not break down. However, in real life, these conditions are hardly ever ideal.
The frequency of different motor damage differs since it depends on different specific
operating conditions.

The induction motor is the most widely used motor in the industry due to its simple and
rugged construction. It requires least maintenance as compared to other electrical motors.
Therefore, induction motor protection plays an important role in its long life service.

Researchers have done costly and limited protection for stator winding protections, broken
rotor bars protection, thermal protection etc. Mainly the induction motor needs protection
from variation of the input supply for small motors which is in common use, not only in big
industry but also in small scale industries. The small scale industries are not able to provide
costly protection to the drives in use as it will increase their capital cost. Therefore a cheap
and compact design has been done for protection of induction motors against unbalanced
voltages, under voltages, short circuits etc.

Most breakdowns are caused by an overload, insulation faults leading to earth faults, turn-to
turn or winding short circuits are caused by excess voltage or contamination by dampness,
oil, grease, dust and chemicals.

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The approximate percentages by these individual faults are:

Table 1-1 Breakdown in Motors

Overload 30%
Insulation damage 20%
Phase Failure 14%
Bearing 13%
Ageing 10%
Rotor damage 5%
Others 8%

1.2 PROBLEM STATEMENT

To guarantee fault-free operation of an electrical drive the following points must be observed:
1. Correct design: a suitable motor has to be selected for each application.
2. Professional operation: professional installation and regular maintenance are
preconditions for fault-free operation
3. Good motor protection: this has to cover all possible problem areas.
 It must not be tripped before the motor is put at risk
 If the motor is put at risk, the protection device has to operate before any
damage occurs.
 If damage cannot be prevented, the protection device has to operate quickly in
order to restrict the extent of the damage as much as possible.

1.3 PROBLEM OBJECTIVE
The objective of this project is to;
1. Design a soft starter of an induction motor by using DSpace.
2. Reduced voltage starting through delayed triggering angle control of TRIAC.
3. Bypass the TRIAC causing direct voltage supply to the motor once the motor reaches
desired speed.

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2. THEORY :

2.1 STARTING:
Starting of an electrical drive involves a change in its state from rest to a steady state speed of
rotation. The process of starting is the most important phenomenon in the entire operation of
the drive. Control of the starting process essentially consists of controlling the acceleration of
the driving motor and the latter is basically a problem of modifying the speed torque
characteristics of the motor in such a way as to obtain the desired starting performance.

Effect of Starting on Power Supply

While studying starting of electric drive systems, it is necessary to consider three factors:
1. Effect of starting upon the power supply.
2. Effect of starting upon the driving motor itself.

The supply network to which the motor is connected may affect the selection of the starting
device from the following viewpoint. The excessive voltage drop due to the peak starting
current may interfere with the supply in such a way that it cannot be tolerated by other
equipment or other consumers connected to the same power supply network.
Since starting is associated with excessive currents, the effect of starting upon the
motor itself must be carefully considered. The starting currents will add to the motor heating
by an amount that depends upon their rms values and upon the frequency of starting. In a dc
motor the limitation may be good communication rather than heating, as dc machines have a
certain maximum limit for the current dictated by the commutation process.

Methods of Starting Electric Motors

The different methods of starting of the various types of electric motors. They are as follows-
1. Full voltage starting: This involves the application of full line voltage to the motor
terminals. This is also called ‘direct-on-line starting’.
2. Reduced voltage starting: In order to avoid heavy starting current and the consequent
voltage dip in the supply lines majority of motors are started by applying a reduced
voltage to their terminals and subsequently increasing it to its normal value.
The starting of a dc motor is, often, accomplished by the addition of suitable external
resistance in the armature circuit and the starting controller is arranged so that this resistance
is short-circuited in steps as the motor comes up to speed.

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Reduced voltage starting of induction motors is achieved by
 Stator resistance starting
 Stator reactor starting
 Star-delta starting
 Autotransformer starting
3. Increased torque starting: With a wound rotor induction motor, resistance can be added
in the rotor circuit so as to decrease the starting current while increasing the starting
torque, even, up to the value of maximum torque that can be developed by the motor.
4. Starting by means of smooth variation of voltage or frequency: With ac motor-dc
generator sets, dc motors can be started by smooth variation of applied voltage and with
variable frequency sources both induction and synchronous motors can be started by
smooth variation of supply frequency, simultaneously varying proportionally the applied
voltage to the motors.

Why the starting current is high in the induction motor?

In an induction motor it takes starting current around 7 times the full load current. The reason
is during starting when we applied a voltage to stator it produce a rotating magnetic field
which is rotating with its synchronous speed. The rotor speed is zero and slip is 100% so a
large amount of magnetic field cuts the rotor surface and produce heavy current to flow from
its and when the rotor catch its speed the amount of field cutting the rotor reduce and slip is
also low and current become normal.

2.2 STATOR VOLTAGE CONTROL METHOD

A very simple and economical method of speed control is to vary the stator voltage at
constant supply frequency. The three-phase stator voltage at line frequency can be controlled
by controlling the switches in the inverter. The developed torque is proportional to the square
of the stator supply voltage and a reduction in stator voltage will produce a reduction in
speed. Therefore, continuous speed control may be obtained by adjustment of the stator
voltage without any alteration in the stator frequency.

=
+ + ( + )

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The Torque speed curves with variable stator voltage control are shown in Fig.

Fig.1: Speed-Torque characteristics with variable stator voltage

The salient features of stator voltage control method are:

 For low-slip motor, the speed range is very low.
 Not suitable for constant-torque load.
 Poor power factor.

Control by ac Voltage Controllers

Domestic fan motors, which are always single-phase, are controlled by a single-phase triac
voltage controller.

Fig.2: Stator voltage control by semiconductor voltage controller

Speed control is obtained by varying firing angle of the triac. These controllers, commonly
known as solid state fan regulators, are now preferred over conventional variable resistance
regulators because of higher efficiency.
Since voltage controllers, allow a stepless control of voltage from its zero value, they are also
used for soft start of motors.

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2.3 Soft Starter:
Soft starters provide all the same functionality as a starter but they allows us to protect the
motor from high spikes and voltage that may cause damage to our motor. They do this by
preventing that large inrush current to our motor by limiting the voltage and current upon
startup. It allows us to slowly ramp up the speed of the motor which causes less wear and
tear. It is used only upon startup however depending upon the model we can see them used in
the shutdown process of a motor.
Once we actually get up to the full load ampere or full speed of our motor it operates the
exact same way as a normal starter.
Advantage:
1. It allows the motor to ramp up slowly to reduce the inrush current to our motor because of
this it saves an operating cost.
2. It allows us to increase the longevity of our motor because we are not putting so much
torque and wear and tearon that motor upon startup.
Disadvantage:
1. It is more expensive than a starter.
2. It does not give full motor speed control.

2.4Induction Motor :

An induction motor always runs at speed less than

synchronous speed. Because the rotating magnetic field

produced in the stator will create flux in the rotor and

hence will make the rotor to rotate.

Fig.3: Cutaway view through stator

of the Induction Motor

Working Principle of Induction Motor :

When we give the supply to the stator winding, a magnetic flux is produced in the stator
due to the flow of current in the coil. The rotor winding is arranged in such a way that
each coil becomes short- circuited in the rotor itself.
The flux from the stator cuts the short-circuited coil in the rotor. As the rotor coils are
short-circuited, according to Faraday's law of electromagnetic induction, current will start

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 flowing through the coil of the rotor. When the current through the rotor coils flows,
another flux gets generated in the rotor. Now there are two fluxes, one is stator flux, and
another is rotor flux. The rotor flux will be lagging with respect to the stator flux.
Because of that, the rotor will feel a torque which will make the rotor to rotate in the
direction of rotating magnetic field.

2.2 dSPACE :
1. With decades of experience, dSPACE knows about the special requirements of
electric drives and hardware-in-the-loop (HIL) simulation. The dSPACE products
work together seamlessly to provide a convenient development and test environment.
They benefit from hardware such as powerful real-time processors, comprehensive
I/O interfaces and so on. dSPACE also offers dedicated function libraries for data
processing and for controller or plant models. Sophisticated software supports the
transition from the first function model in Simulink to comprehensive real-time tests.
dSPACE hardware and software together provide a seamless tool chain whose
individual parts are finely tuned to each other.

2. dSPACE supports customers worldwide from the first controller development to the
last approval tests. Throughout the development process, dSPACE Engineering
Services provide assistance for even the most challenging projects. All this to provide
the greatest flexibility at the highest convenience.

CONTROLLER BOARD OF DS1202 :

Fig. 4 shows the entire dSPACE DS1202 controller board internal structure. dSPACE
controller board forms the main part of the system as it serves as the connecting link
between MATLAB/Simulink inverter model to the real inverter hardware. Some
exclusive interfaces are inbuilt in dSPACE DS1202. The special blocks are only
available in Matlab Simulink with DS1202 controller platform such as DS1202ADC,
DS1202DAC and DS1202BIT_OUT_CX. MATLAB/Simulink Real-Time-Workshop
(RTW) function, can be used convert the interface blocks to the C-code automatically
[8]. Finally, this code is compiled by a compiler and linked to the real-time dSPACE
DS1202 processor board. In addition to this DS1202 also comes with a graphical user
interface (GUI) called Control Desk used for observe the performance of the inverter

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 on an online basis [8]. Various control strategies have been implemented on dSPACE
DS1202 control platform such as deadbeat controller, voltage controlled SPWM etc.
Here a current controlled pulse-width modulation is implemented in synchronous
reference frame. Digital proportional integral (PI) controller is also another method to
obtain better quality waveforms from an inverter. A properly designed PI controller
using analog components is quite a tedious task especially in ac applications but using
DS1202 controller board helps the designer to make the PI controller in Simulink and
link it to the real world.

Fig. 4:CONTROLLER BOARD OF DS1202.

The complex control algorithm as elaborated in the previous section is easily implemented in
Matlab Simulink by employing the ‘Real-Time Workshop’ (RTW) feature inbuilt in
MATLAB/Simulink environment. After creating the model and running the simulation .sdf
file is built which actually converts control system algorithm to an equivalent C-code and
simultaneously linked to the real inverter hardware. Because of this simplicity and
advantages dSPACE DS1202 is very much in use as a development and research tool. To get
the output waveforms in real time some special blocks are to be inserted in the simulink
model; those are, the dSPACE input-output (I/O) library blocks. These blocks are namely:
analog-to digital converter (ADC) units, DS1202ADC, bit input-output (I/O) unit,
DS1202BIT_OUT, and 3-phase PWM generation unit, DS1202SL_DSP_PWM3. DS1202

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and also its other variants are used mainly for building of prototypes as a research tool for
developing real complex control algorithms. Also with increasing number of switching
devices a very effective and error free control strategy can only be built in a system like
dSPACE for its special feature of software and hardware linkage.

Fig.5: Dspace MicroLabBox Toolkit.

2.3 MATLAB :

MATLAB is a high-performance language for technical computing. It integrates

computation, visualization, and programming in an easy-to-use environment where
problems and solutions are expressed in familiar mathematical notation.
Typical uses include:

 Math and computation

 Algorithm development
 Modeling, simulation, and prototyping
 Data analysis, exploration, and visualization
 Scientific and engineering graphics

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 Features of Matlab:-
 Simulink: Simulink® is a block diagram environment for multidomain simulation

 and Model-Based Design. It supports simulation, automatic code generation, and

continuous
 test and verification of embedded systems.

 Language Fundamentals: Syntax, operators, data types, array indexing and

manipulation

 Mathematics: Linear algebra, differentiation and integrals, Fourier transforms, and

other mathematics

 Graphics: Two- and three-dimensional plots, images, animation, visualization

 Data Import and Analysis: Import and export, preprocessing, visual exploration

 Programming Scripts and Functions: Program files, control flow, editing, debugging

 App Building: App development using App Designer, GUIDE, or a programmatic

workflow

 Advanced Software Development: Object-oriented programming; code performance;

unit testing; external interfaces to Java®, C/C++, .NET and other languages

 Desktop Environment: Preferences and settings, platform differences

 Supported Hardware: Support for third-party hardware, such as webcam, Arduino®,

 and Raspberry Pi™ hardware. Also the MicroLab box can be used to get the real time
 output from the Simulink files
About Simulink:
 Simulink® is a block diagram environment for multidomain simulation and Model-Based
Design.
 Simulink provides a graphical editor, customizable block libraries, and solvers for
modeling and simulating dynamic systems. It is integrated with MATLAB®, enabling us
to incorporate MATLAB algorithms into models and export simulation results to
MATLAB for further analysis.
 In this project, our Hardware and Software part both are based on Simulink. In the
software part the whole thing is simulated in Simulink and in the hardware part the

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 control signal is also generated using the Simulink file by getting a real time output using
MicroLab Box and dSPACE software.

3. SOFTWARE IMPLEMENTATION :
3.1 Zero Crossing Detector Circuit :

When signal changes from positive to negative point i.e. crossing axis value become zero this is
known as zero cross detection.

Fig.6: Waveform of ZCD and delayed output

An input signal is applied as shown in fig. 1, we integrate the input signal for every half cycle
shown in fig. 2. After that we take a constant a1 firing angle parallel to x-axis. So, when the
slope of input signal is greater than the constant firing angle then a pulse is generated as
shown in fig. 3. Now again we integrate the firing pulse of fig. 3 and a constant angle a2 is
fired which is parallel to x-axis. In this fig.3, if the slope of the pulse is smaller than the firing
angle then the resultant pulse is obtained which is shown in fig. 4.

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ZCD and delayed output waveform using MATLAB :

Fig.7: ZCD and delayed output waveform using MATLAB .

MAIN SIMULATION CIRCUIT :

Fig.8: Simulink Circuit Diagram (ZCD along with triggering circuit)

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Initially, the Simulink model starts running at 1200 as firing angle of Switch1. The function
of the relation operator is to control the toggle between normally close and normally open
terminal of the switch. When the time constant is greater than equal to 300, then the normally
closed terminal gets open and normally open terminal get closed. In this way 120 0 firing
angle of Switch1 is changed to 900 firing angle.
Switch2 is the main toggling switch. When the time constant is greater than equal to 60 0, then
the normally closed terminal gets open and normally open terminal get closed. In this way
Switch1 and Switch3 can be toggled as per need.
When the time constant is greater than equal to 600, 900 firing angle of Switch1 is changed
450 firing angle of Switch3. When the time constant is greater than equal to 900, then the
normally closed terminal gets open and normally open terminal get closed. In this way 45 0
firing angle of Switch3 is changed to 00 firing angle.

dSpace Control Desk:

dSpace control desk is a universal modular experiment and instrumentation software for
electronic control unit development. It perform all necessary tasks and gives a single working
environment,from the start of the experimentation right to the end.

Fig.13: dSpace Control Desk

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4. HARDWARE IMPLEMENTATION

4.1 BLOCK DIAGRAM

Fig.14: Block Diagram of Soft starter of an Induction Motor

4.2 CIRCUIT DIAGRAM

Fig.15: Circuit Diagram of Soft starter of an Induction Motor

4.3 CIRCUIT DESCRIPTION

When a 5V input pulse is applied to the resistance R1 and R2 respectively. The pulse from
resistance R2 is flowing from Pin1 to Pin2 and the pulse from resistance R1 is flowing from

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transistor Q1 to the ground. So, the LED of MOC3021 is indicated high when the current is
flown from it.

Thus the light produced by this LED activates the diac of MOC3021 to make it conductive
and that time power is switched ON. Now, when we supply 230V to the power circuit, the
current flows from Pin6 to Pin4 and the gate terminal of the TRIAC of power circuit is
trigerred. And the lamp gives the output of the circuit. That is how the soft starter circuitry
works.

4.4 HARDWARE MODEL :

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Fig:16 : LIST OF HARDWARE COMPONENT

 Veroboard
 Opto-Coupler MOC3021
 Triac BT-136
 Transistor BC-547
 Resistors: 0.2k, 0.3k, 10k, 100k
 6V, 500mA Transformer
 Two Pin Plug
 IC Base
 0.1uF 500V Capacitor

4.6 FULL HARDWARE MODEL :

Fig.17: Full hardware circuit board along with 6v transformer

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 Full Setup of Final Testing (Fig. 18) :

This photos contains the final setup of testing our hardware. Using Dspace input signal, we
are trying to start the induction moton with different firing angles.Alongside, we serially
connect a 40W bulb to get better result of changing in firing angle.

Real time Simulation :

Fig.19: Real time Simulation

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4.6 MAIN HARDWARE COMPONENTS USED:

I. Opto-Coupler MOC3021:
MOC3021 is an opto-coupler designed for triggering TRIACS. By using this we can
trigger anywhere in the cycle, so can call them as non-zero opto-coupler. MOC3021
are very widely used and can be quite easily obtained from many sources. It comes in
6-pin DIP shown in figure.

Features:
1. 400V Photo- triac driver output
2. Gallium-Arsenic-Diode Infrared Source and Optically-Coupled Silicon triac driver
3. High isolation 7500V Peak
4. Output Driver Designed for 220Vac
5. Standard 6-terminal plastic DIP

II. TRIAC BT-136:

Triac is a bidirectional semiconductor device with three terminals which is used for
bidirectional current both in positive as well as in negative cycle.

Triac can be triggered by both positive and negative current applied to its gate. There
are many different types of triac. The type of triac that is used in this project is
BT136. Reason for choosing this triac is that it is used in motor control application
with high voltage and current rating which is suitable with induction motor as
compared to other the triacs. It is easy available and inexpensive.

III. TRANSISTOR BC547:

BC547 is a NPN transistor hence the collector and emitter will be left open (Reverse
biased) when the base pin is held at ground and will be closed (Forward biased) when
a signal is provided to base pin. BC547 has a gain value of 110 to 800, this value
determines the amplification capacity of the transistor. The maximum amount of
current that could flow through the Collector pin is 100mA, hence we cannot connect

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 loads that consume more than 100mA using this transistor. To bias a transistor we
have to supply current to base pin, this current (IB) should be limited to 5mA.

IV. TRANSFORMER:

Electrical power transformer is a static device which transform electrical energy from
one circuit to another without any direct electrical connection and with the help of
mutual induction between two windings. It transforms power from one circuit to
another circuit without changing its frequency but may be in different voltage level.

Working Principle of Transformer :

The working principle of transformer is very simple. It depends upon Faraday's law
of electromagnetic induction. Mutual induction between two or more winding is
responsible for transformation action in an electrical transformer.

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OBSERVATION AND RESULTS :

Fig.9: 1200 firing angle

Fig.10: 900 firing angle

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 Fig.11: 450 firing angle

Fig.12: 00 firing angle

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Conclusion :
The main objective of the project is to reduce the terminal voltage of the
induction motor , so that the motor could start smoothly from rest and thereby
increasing the terminal voltage across the motor in steps, as the motor gains
speed. In this way, the starting current of the motor which is 4-6 times of the
full load current. The motor is protected from any electrical disturbances which
can damage the motor. We have successfully build a soft starter by using a triac
and an optocoupler, which can initially reduce the terminal voltage across the
motor during starting and gradually increase the voltage once the motor starts.
Therefore our main objective of this project is successful.

Future Aspect of the project :

Every project work have their own limitations. Similarly, the main limitation of
the project is that we can not vary the speed of the motor as per need as there
are certain limit of triggering pulses.
The future aspect of this project is to measure the speed of a induction motor
using encoder. Encoder changes the measured speed into an electrical signal so
that it can easily fed to a microcontroller. The microcontroller has to be
programmed in such a way that it can control the firing pulses and vary the
speed of the motor for smoothness and as per need.

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 APPENDIX A

V. Opto-Coupler MOC3021:
MOC3021 is an opto-coupler designed for triggering TRIACS. By using this we can
trigger anywhere in the cycle, so can call them as non-zero opto-coupler. MOC3021
are very widely used and can be quite easily obtained from many sources. It comes in
6-pin DIP shown in figure.

Fig. 20: Pin Description of MOC3021

Features:
6. 400V Photo- triac driver output
7. Gallium-Arsenic-Diode Infrared Source and Optically-Coupled Silicon triac driver
8. High isolation 7500V Peak
9. Output Driver Designed for 220Vac
10. Standard 6-terminal plastic DIP

There are many application of MOC3021 such as solenoid/valve controls, lamp

ballasts, interfacing microprocessors to 115/240 Vac peripherals, motor controls and
incandescent lamp dimmers.

Application of MOC3021:
From the below circuit, the most commonly used is an opto-coupler MOC3021 with an
LED diac type combination. Additionally while using this with microcontroller and
one LED can be connected in series with MOC3021, LED to indicate when high is
given from micro-controller such that we can know current is flowing internal LED of

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 the opto-coupler. When logic high is given then the current flows through the LED
from pin 1 to 2. So in this process LED light falls on DIAC causing 6 and 4 to close.
During each half cycle current flows through gate, series resistor and through opto-
diac for the main thyristor/triac to trigger for the load to operate.

VI. TRIAC BT-136:

Triac is a bidirectional semiconductor device with three terminals which is used for
bidirectional current both in positive as well as in negative cycle.

Triac can be triggered by both positive and negative current applied to its gate. There
are many different types of triac. The type of triac that is used in this project is
BT136. Reason for choosing this triac is that it is used in motor control application
with high voltage and current rating which is suitable with induction motor as
compared to other the triacs. It is easy available and inexpensive.

Fig.21 Pin Description of TRIAC BT-136

Features of BT136:

 Direct triggering from low power drivers and logic Ics.

 High blocking voltage capability.
 Low holding current for low current loads and lowest EMI at commutation.
 Sensitive gate.
 Triggering in all four quadrants.

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 Applications of BT136:

 Universally useful in motor control.

 General purpose switching.

VII. TRANSISTOR BC547:

BC547 is a NPN transistor hence the collector and emitter will be left open (Reverse
biased) when the base pin is held at ground and will be closed (Forward biased) when
a signal is provided to base pin. BC547 has a gain value of 110 to 800, this value
determines the amplification capacity of the transistor. The maximum amount of
current that could flow through the Collector pin is 100mA, hence we cannot connect
loads that consume more than 100mA using this transistor. To bias a transistor we
have to supply current to base pin, this current (IB) should be limited to 5mA.

Fig.22 Pin Description of BC-547

BC547 acts as SWITCH

When a transistor is used as a switch it is operated in the Saturation and Cut-Off

Region as explained above. As discussed a transistor will act as an Open switch
during Forward Bias and as a Closed switch during Reverse Bias, this biasing can be
achieved by supplying the required amount of current to the base pin. As mentioned
the biasing current should maximum of 5mA. Anything more than 5mA will kill the

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 Transistor; hence a resistor is always added in series with base pin. The value of this
resistor (RB) can be calculated using below formulae.

Where, = 5V for BC547.

= does not exceed mA.

VIII. TRANSFORMER:

Electrical power transformer is a static device which transform electrical energy from
one circuit to another without any direct electrical connection and with the help of
mutual induction between two windings. It transforms power from one circuit to
another circuit without changing its frequency but may be in different voltage level.

Working Principle of Transformer :

The working principle of transformer is very simple. It depends upon Faraday's law
of electromagnetic induction. Mutual induction between two or more winding is
responsible for transformation action in an electrical transformer.

Basic Theory of Transformer :

We have one winding which is supplied by an alternating electrical source. The
alternating current through the winding produces a continually changing flux or
alternating flux that surrounds the winding. If any other winding is brought nearer to
the previous one, obviously some portion of this flux will link with the second. As this
flux is continually changing in its amplitude and direction, there must be a change in
flux linkage in the second winding or coil. According to Faraday's law of
electromagnetic induction, there must be an EMF induced in the second. If the circuit
of the later winding is closed, there must be a current flowing through it. This is the
simplest form of an electrical power transformer, and this is the most basic of working
principle of transformer.

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Fig. 23: Working of Transformer

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Page 34
 NPN General Purpose Amplifier
(continued)

Electrical Characteristics TA = 25°C unless otherwise noted

Symbol Parameter Test Conditions Min Max Units

OFF CHARACTERIS TICS

V
(BR)CEO Collector-Emitter Breakdow n Voltage IC = 1.0 mA, IB = 0 45 V
V
(BR)CBO Collector-Bas e Breakdown Voltage IC = 10 A, IE = 0 50 V
V
(BR)CES Collector-Bas e Breakdown Voltage IC = 10 A, IE = 0 50 V
V
(BR)EBO Emitter-Base Breakdow n Voltage IE = 10 A, IC = 0 6.0 V
I CBO Collector Cutoff Current V CB = 30 V, IE = 0 15 nA
VCB = 30 V, I E = 0, T A = +150 C 5.0 A

ON CHARACTERISTICS
hFE DC Current Gain V CE = 5.0 V, IC = 2.0 mA 547 110 800
547A 110 220
547B 200 450
547C 420 800
V CE(sat) Collector-Emitter Saturation Voltage IC = 10 mA, IB = 0.5 mA 0.25 V
IC = 100 mA, IB = 5.0 mA 0.60 V
V BE(on) Base-Emitter On Voltage V CE = 5.0 V, IC = 2.0 mA 0.58 0.70 V
V CE = 5.0 V, IC = 10 mA 0.77 V

SMALL SIGNA L CHARA C T E RIS TIC S

hfe Small-Signal Current Gain IC = 2.0 mA, V CE = 5.0 V, 125 900
f = 1.0 kHz
NF Noise Figure V CE = 5.0 V, IC = 200 A, 10 dB
RS = 2.0 k, f = 1.0 kHz,
BW = 200 Hz

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Page 36
Philips Semiconductors Product specification

Triacs BT136 series D

logic level

STATIC CHARACTERISTICS
Tj = 25 ˚C unless otherwise stated
SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT
I
GT Gate trigger current VD = 12 V; IT = 0.1 A
T2+ G+ - 2.0 5 mA
T2+ G- - 2.5 5 mA
T2- G- - 2.5 5 mA
I T2- G+ - 5.0 10 mA
L Latching current VD = 12 V; IGT = 0.1 A
T2+ G+ - 1.6 10 mA
T2+ G- - 4.5 15 mA
T2- G- - 1.2 10 mA
T2- G+ - 2.2 15 mA
IH Holding current VD = 12 V; IGT = 0.1 A - 1.2 10 mA
V
T On-state voltage IT = 5 A - 1.4 1.70 V
V
GT Gate trigger voltage VD = 12 V; IT = 0.1 A - 0.7 1.5 V
I VD = 400 V; IT = 0.1 A; Tj = 125 ˚C 0.25 0.4 - V
D Off-state leakage current VD = V DRM(max); Tj = 125 ˚C - 0.1 0.5 mA

DYNAMIC CHARACTERISTICS
Tj = 25 ˚C unless otherwise stated
SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT
dVD/dt Critical rate of rise of VDM = 67% V DRM(max); Tj = 125 ˚C; - 5 - V/µ s
off-state voltage exponential w aveform; RGK = 1 kΩ
tgt Gate controlled turn-on ITM = 6 A; V D = V DRM(max); IG = 0.1 A; - 2 - µs
time dIG/dt = 5 A/µ s

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References :

 Fundamental of Electric Drive by GK Dubey

 Electrical Machine By Ashfaque Hussain

 A First course on Electric Drive By Sk Pillai

 dSpace Microlab toolkit manual

 Wikipedia
 Datasheet from farnell.com
 Dspace.com
 IEEE module on Soft Starting etc.

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