Design and Fabrication of Three Phase BLDC Motor for Railway Application

DESIGN AND FABRICATION OF THREE PHASE BLDC
MOTOR FOR RAILWAY APPLICATION
PROJECT REPORT
Submitted in partial fulfillment of the requirements for the award of the degree of
Bachelor of Technology in ELECTRICAL AND ELECTRONICS
ENGINEERING of Mahatma Gandhi University
By
AMAL JOSEPH K
ANOOP S
ASHISH JACOB JAMES
FAHEEM ALI T
HOSNI K
JACOB MATHEW K
DEPARTMENT OF ELECTRICAL ENGINEERING
RAJIV GANDHI INSTITUTE OF TECHNOLOGY
KOTTAYAM-686501
2009-2013

DEPARTMENT OF ELECTRICAL ENGINEERING
2009-2013
RAJIV GANDHI INSTITUTE OF TECHNOLOGY
KOTTAYAM - 686501
CERTIFICATE
This is to certify that the report entitled “DESIGN AND FABRICATION OF THREE
PHASE BLDC MOTOR FOR RAILWAY APPLICATIONS” is a bonafide record of the
project done by Amal Joseph K, Anoop S, Ashish Jacob James, Faheem Ali T, Hosni K,
Jacob Mathew K towards the partial fulfillment of the requirement for the award of
Bachelor of Technology in Electrical and Electronics Engineering of the Mahatma
Gandhi University.
Project Guide Head of Department
Prof. JijiK S Prof. Vijayakumari C K
Dept. of Electrical Engineering Dept. of Electrical Engineering

acknowledgement
Words are not enough to praise the lord, the almighty whose blessings
led us to the successful completion of our project.
We have great pleasure to express our obligations to our project guide
Prof. Jiji K S for her effective motivation, helpful feedback and timely
assistance for the completion of our project.
We would also like to express our gratitude to Prof.Vijayakumari (HOD,
Department of Electrical Engineering) and all our teachers of Electrical
department for their valuable advice and guidance.
Finally we wish to thank our parent’s, family members, friends as well as
well-wishers for their moral support rendered to us for finishing our project
successfully.
Amal Joseph K
Anoop S
Ashish Jacob James
Faheem Ali T
Hosni K
Jacob Mathew K

Kel
Established in 1964 in the State of Kerala, India, Kerala Electrical & Allied Engineering
Co.Ltd. (KEL) is a multifaceted company fully owned by the State government. Through its five
production facilities, located in various districts of the State, this ISO 9001 : 2000 complaint
company provides basic engineering services / products besides executing projects of national
significance for high profile clients like the various defense establishments.
The company manufactures and markets products like general purpose brushless
alternators, brushless alternators for lighting and air-conditioning of rail coaches, medium power
and distribution transformers as well as structural steel fabrications.
The product categories for defense applications include high frequency alternators,
frequency convertors, special alternators and power packs for missile projects. The power packs
designed and supplied by the company for missile projects like Falcon, Prithvi, Trishul and
Akash were the pioneering efforts. The company has also supplied special alternators to the
Army (Military Power Cars) and Air Force (Radar Applications).
The company's all-India marketing network with regional offices in all metro cities cater
to major institutional clients like the State Electricity Boards, Indian Railways and various
defense establishments besides the general market clients.

ABSTRACT
The objective of the project is to design and build the prototype of a three phase sensor
less BLDC motor for railway application. The motor is designed according to the specifications
put forward by RDSO for the design of BLDC carriage fan. Traditionally, BLDC motors are
commutated in six-step pattern with commutation controlled by position sensors. To reduce cost
and complexity of the drive system, sensor less drive is preferred. In this project an open loop
control for BLDC motor is presented.
Brushless DC motors are increasingly replacing brushed DC motors in low- to medium-
power servo applications. In these motors, electronic commutation is used in lieu of mechanical
brushes. This reduces friction, increases reliability, and decreases the cost to produce the motor
itself. Due to the absence of brushes better speed range is possible for BLDC motors and the
maintenance cost will also be less. The Brushless DC motor is the ideal choice for applications
that require high reliability, high efficiency, and high power-to-volume ratio. When operated in
rated conditions, the BLDC motors have a life expectancy of over 10,000 hours. For long term
applications, this can be a tremendous benefit and hence it is a proper choice for railway carriage
fans.

contents
1) Chapter 1 Introduction 1
2) Chapter 2 Project overview 7
3) Chapter 3 Design 8
4) Chapter 4 Fabrication 13
5) Chapter 5 Control circuit 26
6) Chapter 6 Conclusion 34
7) Chapter 7 Future scope 35
8) Chapter 8 Manufacturing Cost 36
9) References 37
10) Appendix 38

list of figures
1. Slotted and slot less BLDC motor
2. Interior and exterior rotor
3. BLDC motor working
4. CAD drawing of Stator
5. Drawing of Rotor
6. CAD drawing of Stator with Rotor
7. Stator manufacturing process
8. Stator stamping
9. Stacked Stator
10. Wound Stator
11. Prepped Stator
12. Stator Assembly
13. B – H Characteristics of a ferromagnetic material
14. Rotor magnet
15. Rotor manufacturing process
16. Shaft
17. Hub
18. Rotor magnet glued to hub
19. Bearing
20. Housing with stator
21. Assembled BLDC motor
22. Block diagram of control circuit
23. Intel 8051
24. Flowchart for 8051 controller
25. Circuit diagram of gate driver circuit using 8051
26. 8051 interface
27. Gate driver waveform from 8051 circuit
28. MCT 2E Optocoupler
29. Gate driver circuit
30. Circuit diagram- Inverter circuit
31. Inverter circuit

Design and fabrication of three phase BLDC motor for railway applications
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CHAPTER 1
INTRODUCTION
In a typical DC motor, there are permanent magnets on the outside and a spinning
armature on the inside. The permanent magnets are stationary, so they are called the stator and
the armature rotates, so it is called the rotor.
The armature contains an electromagnet. When excitation is given to this electromagnet, it
creates a magnetic field in the armature that attracts and repels the magnets in the stator. So the
armature spins. To keep it spinning, the polarity of the electromagnet is to be changed. The
brushes handle this change in polarity. They make contact with two spinning electrodes attached
to the armature and flip the magnetic polarity of the electromagnet as it spins. But the brushed
DC motors have many disadvantages. Some of them are listed below:
 The brushes eventually wear out.
 Because the brushes are making/breaking connections, there is sparking and electrical
noise.
 The brushes limit the maximum speed of the motor.
 Having the electromagnet in the center of the motor makes it harder to cool.
 The use of brushes puts a limit on how many poles the armature can have
The brushless DC motors overcome these disadvantages and are gaining popularity. They are
being used in industries such as appliances, automotive, aerospace and instrumentation. A typical
brushless motor has permanent magnets which rotate and a fixed armature, eliminating problems
associated with connecting current to the moving armature. An electronic controller replaces the
brush/commutator assembly of the brushed DC motor, which continually switches the phase to
the windings to keep the motor turning. The controller performs similar timed power distribution
by using a solid-state circuit rather than the brush/commutator system.

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1.1. BLDC MOTOR
BLDC motors are similar to synchronous motors in working. This means the magnetic
field generated by the stator and the magnetic field generated by the rotor rotates at the same
frequency. BLDC motors do not experience the “slip” that is normally seen in induction motors.
BLDC motors come in single-phase, 2-phase and 3-phase configurations. Corresponding to its
type, the stator has the same number of windings. Out of these, 3-phase motors are the most
popular and widely used.
STATOR
The stator of BLDC motor is made out of laminated steel stacked up to carry the
windings. Windings in a stator can be arranged in two patterns; i.e. a star pattern (Y) or delta
pattern (∆). The major difference between the two patterns is that the Y pattern gives high torque
at low RPM and the ∆ pattern gives low torque at low RPM. This is because in the ∆
configuration, half of the voltage is applied across the winding that is not driven, thus increasing
losses and, in turn, efficiency and torque. Steel laminations in the stator can be slotted or slotless
as shown in figure 1(a) and 1(b).
Figure 1: Slotted and slot less BLDC motor
(a): Slotted motor (b): Slotless motor

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A slotless core has lower inductance, thus it can run at very high speeds. Because of the
absence of teeth in the lamination stack, requirements for the cogging torque also go down, thus
making them an ideal fit for low speeds too (when permanent magnets on rotor and tooth on the
stator align with each other, because of the interaction between the two, an undesirable cogging
torque develops and causes ripples in speed). The main disadvantage of a slotless core is higher
cost because it requires more winding to compensate for the larger air gap. Proper selection of
the laminated steel and windings for the construction of stator are crucial to motor performance.
ROTOR
The rotor of a typical BLDC motor is made out of permanent magnets. Depending upon
the application requirements, the number of poles in the rotor may vary. Increasing the number
of poles gives better torque but at the cost of reducing the maximum possible speed. Another
rotor parameter that impacts the maximum torque is the material used for the construction of
permanent magnet; the higher the flux density of the material, the higher the torque. There are
mainly 2 types of rotor construction: interior and exterior.
Figure 2: Interior and exterior rotor
(a): Exterior rotor (b): Interior rotor

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In the exterior rotor design, the windings are located in the core of the motor. The rotor
magnets surround the stator windings as shown in figure 2(a). The rotor magnets act as an
insulator, thereby reducing the rate of heat dissipation from the motor. Due to the location of
stator windings, outer rotor designs typically operate at lower duty cycles or at a lower current.
The primary advantage of an external rotor BLDC motor is relatively low cogging torque.
In an interior rotor design, the stator windings surround the rotor and are affixed to the
motors housing as shown in figure 2(b). The primary advantage of interior rotor design is better
heat dissipation. A motor‟s ability to dissipate heat directly impacts its ability to produce torque.
Another major advantage of interior rotor design is lower rotor inertia. For this reason, the
overwhelming majority of BLDC motors use an interior rotor design.

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1.2 WORKING
The underlying principle for the working of a BLDC motor is the same as for a brushed
DC motor; i.e., internal shaft position feedback. In case of a brushed DC motor, feedback is
implemented using a mechanical commutator and brushes. Within a BLDC motor, it is achieved
using multiple feedback sensors. The most commonly used sensors are hall sensors and optical
encoders. In a commutation system two of the three electrical windings are energized at a time as
shown in figure 3.
Figure 3(e): Phase 5
Figure 3(c): Phase 3
Figure 3(a): Phase 1 Figure 3(b): Phase 2
Figure 3(d): Phase 4
Figure 3(f): Phase 6
Figure 3: BLDC motor working

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In figure 3(a), the GREEN winding is energized as the NORTH pole and the BLUE
winding is energized as the SOUTH pole. Because of this excitation, the SOUTH pole of the
rotor aligns with the GREEN winding and the NORTH pole aligns with the RED winding. In
order to move the rotor, the “RED” and “BLUE” windings are energized in the direction shown
in figure 3(b). This causes the RED winding to become the NORTH pole and the BLUE winding
to become the SOUTH pole. This shifting of the magnetic field in the stator produces torque
because of the development of repulsion (Red winding – NORTH-NORTH alignment) and
attraction forces (BLUE winding – NORTH-SOUTH alignment), which moves the rotor in the
clockwise direction. This torque is at its maximum when the rotor starts to move, but it reduces
as the two fields align each other. Thus, to preserve the torque or to build up the rotation, the
magnetic field generated by stator should keep switching. To catch up with the field generated by
the stator, the rotor will keep rotating. Since the magnetic field of the stator and rotor both rotate
at the same frequency, they come under the category of synchronous motor.
This switching of the stator to build up the rotation is known as commutation. For 3-
phase windings, there are 6 steps in the commutation; i.e., 6 unique combinations in which motor
windings will be energized.

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CHAPTER 2
PROJECT OVERVIEW
The objective of the project is to design, develop and analyze the performance of a three
phase BLDC Motor for railway applications
The project involves the following phases
1. The design of three phases BLDC Motor according to the RDSO (Research Design &
Standards Organization) specifications.
2. The fabrication of the motor according to the design.
3. Design and implementation of the control circuit

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Chapter 3
DESIGN
The design parameters of the motor are based on the specifications put forward by
RDSO. The input voltage to the fan is 110 V and the input power is 32 W. The design constraints
for stator rotor and shaft are given below.
STATOR DESIGN
The stator design was done considering the specifications given below.
• No. of phases : 3
• No. of slots : 6
• No. of turns : 435-480
• Stack length : 11.5 ± 0.5
• Stack outer dia : 87mm
• Stack inner dia :56.2 ± 0.2mm
The design of stator thus includes determining the slot area, number of conductors per slot and
slot width.
• Width of stator teeth
• Total no of conductors

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• No of conductors per slot
• Area of stator slot
T = rated torque, Nm
I = phase current, A
kw = winding factor
Z = total number of conductors
p = number of poles
Biron = iron back saturation flux density, T
Bg = Maximum flux density in the air gap, T
L = machine active length, m
D = air gap diameter, m
Dis = stator inner diameter, m
hs = height of stator slot, m
Q = number of slots
q = number of slots per pole-phase
bts = width of stator teeth, m
Aslot = slot area, m2
Considering the design constraints and output of the motor, the stator slots were designed
using CAD.

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Figure 4: CAD drawing of stator

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ROTOR DESIGN
As per the specification of RDSO, the rotor magnet needs to have a magnetic gauss in the
range 1300 – 2000.
Figure 5: Drawing of rotor

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Figure 6: CAD drawing of stator with rotor

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STAMPING STACKING
STACK
INSULATION
WINDING PREPPING
CHAPTER 4
FABRICATION
4.1. STATOR MANUFACTURING
The stator manufacturing process includes the process of cutting the stator laminations,
stacking, insulating and winding the stator conductors. The stator manufacturing process is done
in five main steps as shown in the figure.
STAMPING
The first step is to stamp the laminations in the right geometry with a suitable stamping
die and stamping press. This is a critical stage of the manufacturing process. A poorly designed
lamination or a poorly manufactured lamination can cause heating, loss of efficiency and
problems in final assembly. There are mainly two types of laminations used for stator
manufacturing of BLDC motors, Cold Rolled Grain Oriented (CRGO) and Cold Rolled Non
Grain Oriented Silicon Steel (CRNGO) silicon steel. Cold Rolled Grain Oriented (CRGO) sheets
will have superior magnetic properties in the direction of rolling. The crystals are aligned in the
direction by cold rolling followed by heat treatment process. Magnetic properties of the CRGO
steel laminations are dependent on the magnetic properties of the individual crystals of the
material and the direction of orientation of the crystal. CRNGO is less expensive than CRGO,
and is used when cost is more important than efficiency and for applications where the direction
of magnetic flux is not constant, as in electric motors and generators with moving parts. It is used
when there is insufficient space to orient components to take advantage of the directional
properties of grain-oriented electrical steel. For the construction of the BLDC motor M 45
CRNGO silicon steel laminations of 0.5 mm thickness were used.
Figure 7: Stator manufacturing process

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STACKING
Once the laminations are stamped, they are stacked using a variety of processes such as
notching, gluing, welding or pinning. For the BLDC motor developed, copper rivets of 0.3 mm
were used for the stacking process. As the design specification demands a stator height of 11
mm, 22 stator laminations were stacked together for the stator.
Figure 8: Stator stamping
Figure 9: Stacked stator

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SLOT INSULATION
The next step is to insulate the stack with a proper material to insulate the copper wire
from the sharp edges of the steel lamination stack. Plastic insulators are used for high volume
applications and in some cases paper insulators are also used. Insulation is done mainly to
prevent shorting of the winding wire in the slots to the stack. The insulation material must
provide the needed electrical isolation but it also needs to be very thin in order not to occupy too
much of the valuable slot space. The integrity of the insulation is checked by conducting „high
pot‟ test. In this test the voltage is increased to a high value, normally 1500V, to see if the
insulation can withstand that particular voltage. For the BLDC motor developed, Nomex paper is
used for the slot insulation.
WINDING
Winding is the most crucial part of motor construction as it determines all the electrical
properties. The number of turns and the size of wire to be used is determined from the motor
parameters. The size of conductor is expressed in SWG. Since the BLDC motor is developed for
low power applications i.e of the range of 32 W, dual coated Copper round wires are used. The
stator windings are star connected and their leads are taken out to give supply to the windings.
The star point is connected internally.
Figure 10: Wound stator

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PREPPING
Once the winding procss is completed the ends of the wires need to shaped and
connectors are attached to it. The winding is varnished to keep the wires in place after which the
stator is ready for final assembly. This process is called prepping. Plastic reels are inserted at the
joining ends to avoid short circuit between conductors.
Once the stator assembly is completed the stator windings are subjected to continuity test
and earth fault test. In continuity test, the continuity of the windings are checked using a
multimeter. The earth fault check is done to ensure that there will not be any contact beteween
Figure 11: Prepped stator

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the conductor and the stator laminations. It is done using an earth megger. The earth megger also
gives the winding resistance of the motor.
Figure 12: Stator assembly

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4.2. ROTOR MAGNET
The rotor of a BLDC motor is made up of permanent magnets glued or fixed to a shaft.
The permanent magnets used in BLDC motor are mostly of rare earth materials. The magnetic
properties of a material can be obtained from the hysterisis loop. A hysterisis loop shows the
relationship between the induced magnetic flux density (B) and the magnetizing force (H). it is
often referred as the B-H curve or B-H loop.
Figure 13: B-H characteristics of a ferromagnetic material
The B-H curve is generated by measuring the magnetic flux of a ferromagnetic material
while the magnetizing force is changed. A ferromagnetic material that has never been previously
magnetized or has been thoroughly demagnetized will follow the dashed line as H is increased.
As the line demonstrates, the greater the amount of current applied (H+), the stronger the
magnetic field in the component (B+). At point "a" almost all of the magnetic domains are
aligned and an additional increase in the magnetizing force will produce very little increase in
magnetic flux. The material has reached the point of magnetic saturation. When H is reduced to

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zero, the curve will move from point "a" to point "b." At this point, it can be seen that some
magnetic flux remains in the material even though the magnetizing force is zero. This is referred
to as the point of retentivity on the graph and indicates the remanence or level of residual
magnetism in the material. As the magnetizing force is reversed, the curve moves to point "c",
where the flux has been reduced to zero. This is called the point of coercivity on the curve. The
force required to remove the residual magnetism from the material is called the coercive force or
coercivity of the material.
As the magnetizing force is increased in the negative direction, the material will again
become magnetically saturated but in the opposite direction (point "d"). Reducing H to zero
brings the curve to point "e." It will have a level of residual magnetism equal to that achieved in
the other direction. Increasing H back in the positive direction will return B to zero. Notice that
the curve did not return to the origin of the graph because some force is required to remove the
residual magnetism. The curve will take a different path from point "f" back to the saturation
point where it with complete the loop.
From the hysteresis loop, a number of primary magnetic properties of a material can be
determined.
1. Retentivity (Br) - A measure of the residual flux density corresponding to the saturation
induction of a magnetic material. In other words, it is a material's ability to retain a
certain amount of residual magnetic field when the magnetizing force is removed after
achieving saturation. (The value of B at point b on the hysteresis curve.)
2. Residual Magnetism or Residual Flux - the magnetic flux density that remains in a
material when the magnetizing force is zero. The residual magnetism and retentivity are
the same when the material has been magnetized to the saturation point. However, the
level of residual magnetism may be lower than the retentivity value when the
magnetizing force did not reach the saturation level.
3. Coercive Force (Hc) - The amount of reverse magnetic field which must be applied to a
magnetic material to make the magnetic flux return to zero. (The value of H at point c on
the hysteresis curve.)

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4. Permeability, m - A property of a material that describes the ease with which a magnetic
flux is established in the component.
5. Reluctance - Is the opposition that a ferromagnetic material shows to the establishment
of a magnetic field. Reluctance is analogous to the resistance in an electrical circuit.
For construction of the BLDC motor Neodymium magnet is used. It is a rare earth magnet
and is made from an alloy of neodymium, iron and boron to form the Nd2Fe14B tetragonal
crystalline structure. It has a Br value of 9200 gauss and Hc value of 6000 oersted. The rotor for
the motor has a magnetic fied strength of 1400 gauss. It is 4 pole magnet with ring structure.
Figure 14: Rotor magnet

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4.3 ROTOR MANUFACTURING
Rotor assembling process includes the machining of shaft and hub to attach the rotor
magnet. The steps involved in rotor manufacturing process is as shown:
Figure 15: Rotor manufacturing process
SHAFT MACHINING
The rotor manufacturing starts with the machining of the stainless steel shaft. The rotor
magnet and bearing are attached to the shaft. To the other end of the shaft threading is provided
to attach the fan blades.
SHAFT
MACHINING
HUB MACHINING
MAGNET
GLUING
BEARING
PRESS
Figure 16: Shaft

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HUB MACHINING
Hub is a round piece of steel with right diameter for the magnets to be glued on to it. The
hub is normally made from powder metals as the material cost is low. The ID and OD of the hub
are critical for trouble free assembly of the shaft and the magnets.
Figure 17: Hub

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MAGNET GLUING
Magnets are typically bonded Neo rings for smaller motors and sintered Neo pole pieces
for larger motors. These magnets are glued on to the hub. The gluing process is not trivial at all
and has been perfected by each individual manufacturer based on years of experience. Kevlar
tape or a steel band is added over the magnets for extra security especially for rotors which are to
be used in high speed applications.
Figure 18: Rotor magnet glued to hub
BEARING PRESS
At this stage, the bearings are pressed on and the rotor is ready to mate with the rest of
the parts in final assembly. Care has been taken with appropriate fixtures to avoid improper
seating of the bearings. The bearing used for the motor is 2RS 6000. It has inner dia of 10 mm.
2RS represents that it is rubber sealed in two sides. The advantage of rubber sealed bearings is
that it offers better heat dissipation.
Figure 19: Bearing

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HOUSING
The housing of the motor is made up of mild steel. The stator is fixed to the housing so
that it remains still during the operation. The ball bearings are pressed on to the housing properly
so that the rotor assembly is properly balanced between the stator poles for the smooth operation
of the motor.
Figure 20: Housing with stator

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Figure 21: Assembled BLDC motor

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CHAPTER 5
CONTROL CIRCUIT
BLDC motor control system mainly comprises of DC voltage source, power electronics
inverter, rotor position sensor, and digital controller. It is known that induction AC motors and
conventional DC motors can run by just connecting them to AC or DC power supplies directly as
their working does not depend on the information about their rotor position. However, BLDC
motor control systems perform electronic commutations through a power electronic inverter as
mechanical brushes and commutators are absent in BLDC motors.
There are two types of control possible in three phase BLDC motor. Open loop control
and closed loop control. In closed loop control, the control systems need rotor position
information during operation to generate commutation pulses. In open loop control the control
system will not have a feedback path i.e. it will not detect the rotor position, it generates the
commutation pulses according to the predefined control algorithm. In this project, the open loop
control of the three phase BLDC motor is implemented.
The principle of open loop control is to initially run the motor at reduced speed and then
the speed is increased in steps to reach the rated speed. The speed is increased in steps to prevent
the locking of rotor which is also termed as cogging.
Figure 22: Block diagram of control circuit
8051 MC
DRIVING
CIRCUIT
THREE
PHASE
INVERTER
MOTOR

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The Intel 8051 IC is used to generate pulses that are fed to the driver circuit of a
MOSFET inverter. The output of the three phase inverter is connected to the three windings of
the motor. Normally it takes six steps to complete an electrical cycle. With every 60 electrical
degrees, the phase current switching is synchronously updated. However, one electrical cycle
may not correspond to a complete mechanical revolution of the rotor. The number of electrical
cycles to be repeated to complete a mechanical rotation is determined by the rotor pole pairs. For
each rotor pole pairs, one electrical cycle is completed. So, the number of electrical
cycles/rotations equals the rotor pole pairs.
INTEL 8051
The Intel 8051 is a single chip microcontroller (µC) series which was developed
by Intel for use in embedded systems. In this project, the microcontroller IC 8051 is used to give
the gate driving pulses to the inverter circuit. The gate pulses are given in two steps. At the
starting time the input to the motor is at a reduced speed and once the rotor catches up with the
stator poles the motor is operated at its rated speed, 600 rpm.
Figure 23: Intel 8051

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Figure 24: Flowchart for 8051 controller
START
Load starting address
Set input and output pins
Square wave subroutine with time period 160 milli
seconds (corresponding to 300 rpm of motor)
Check for interrupt
Square wave subroutine with time period 45 milli
seconds (corresponding to 600 rpm of motor)
STOP
No
Yes

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Figure 25: Circuit diagram of gate driver circuit using 8051

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Figure 26: 8051 Interface
Figure 27: Gate driver waveform from 8051 circuit

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GATE DRIVING CIRCUIT
The output pulses from the 8051 are given to a gate driving circuit. The gate driving
circuit is designed using an optocoupler. An optocoupler or opto-isolator is a component that
transfers electrical signals between two isolated circuits by using light. Opto-isolators
prevent high voltages from affecting the system receiving the signal. A common type of opto-
isolator consists of an LED and a phototransistor in the same package. Opto-isolators are usually
used for transmission of digital (on/off) signals. Hence they can be used in gate driving circuits
of inverters. An opto-isolator contains a source (emitter) of light, almost always a near
infrared light-emitting diode (LED), that converts electrical input signal into light, a closed
optical channel (also called dielectrical channel), and a photo sensor, which detects incoming
light and either generates electric energy directly, or modulates electric current flowing from an
external power supply. The sensor can be a photo resistor, a photodiode, a phototransistor,
a silicon-controlled rectifier (SCR) or a triac. Because LEDs can sense light in addition to
emitting it, construction of symmetrical, bidirectional opto-isolators is possible. An
optocoupled solid state relay contains a photodiode opto-isolator which drives a power switch,
usually a complementary pair of MOSFETs. A slotted optical switch contains a source of light
and a sensor, but its optical channel is open, allowing modulation of light by external objects
obstructing the path of light or reflecting light into the sensor. For the project we have used
MCT2E optocoupler.
Figure 28: MCT2E optocoupler

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Figure 29: Gate driving circuit
INVERTER CIRCUIT
A three phase BLDC motor is fed from a three phase inverter circuit with stepped output
waveform. Each output line is connected to the input terminals of the BLDC motor. A basic
three-phase inverter consists of three single-phase inverter switches each connected to one of the
three load terminals. For the most basic control scheme, the operation of the three switches is
coordinated so that one switch operates at each 60 degree point of the fundamental output
waveform. This creates a line-to-line output waveform that has six steps. The six-step waveform
has a zero-voltage step between the positive and negative sections of the square-wave such that
the harmonics that are multiples of three are eliminated as described above. When carrier-based
PWM techniques are applied to six-step waveforms, the basic overall shape, or envelope, of the
waveform is retained so that the third harmonic and its multiples are cancelled.

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Figure 30: Circuit diagram of inverter
Since the BLDC motor is developed for low power application, IRF 840 N channel MOSFET are
used as it is suitable for low power applications.
Figure 31: Inverter circuit

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chapter 6
CONCLUSION
The project deals with the complete engineering process behind the design and
manufacturing of a three phase BLDC motor. A thorough understanding of the motor model is
important for the successful design of the motor. The current design is of a BLDC motor with 6
stator 4 rotor poles. As the prototype uses an open loop control, the motor was not driven to its
full potential. Even with the controller limitations the motor was able to deliver a fan speed of
400 rpm. By using specialized BLDC motor controller IC‟s like A4960, the prototype will be
fully functional and can deliver maximum torque and can offer better efficiency.

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Chapter 7
FUTURE SCOPE
Although the project has produced a working prototype, there is still room for future
advancements. With better resources, closed loop control can be implemented. For the closed
loop control, the rotor position needs to be known. In order to obtain the rotor pole position
either mechanical or electronic hardware sensor is used. However, the cost of mechanical rotor
position sensors like encoder, tachometer, resolver and Hall Effect sensor are expensive which
led to the development of sensorless control. There are various kinds of sensorless controls of
BLDC motors. Back EMF based method, high frequency current injection method, and observer
based methods are some of them to mention. Specialized three phase BLDC motor controller
IC‟s like A4960 are available in market for implementation of sensorless control of BLDC
motors.

Page | 36
Chapter 8
MANUFACTURING COST
ITEM PRICE QUANTITY TOTAL(Rs)
M-45 CRNGO silicon
steel
400/kg 680 gm. 272
Rotor magnet 125 1 125
Labour for Stamping 300/ hr. 5 hr. 1500
29 SWG Cu wire 740/kg 175 gm. 130
6000 2RS bearing 35 1 35
Labour cost for Lathe
work
3000 1 3000
IC 8051 75 1 75
Circuit components 1785 1 1785
Total Rs.6972

Page | 37
References
1. RDSO specification No.RDSO/PE/SPEC/TL/0021/2005(REV„2‟), technical specification
for brushless DC railway carriage fan.
2. Weimin Wang, Kwanghee Nam, Sung-young Kim, “Concentric Winding BLDC Motor
Design”, IEEE International Conference on Electric Machines and Drives, Page(s) 157-
161, 2005
3. Jun-Hyuk Choi , Se-Hyun You , Jin Hur , Ha-Gyeong Sung, “The Design and Fabrication
of BLDC Motor and Drive for 42V Automotive Applications”, IEEE International
Symposium on Industrial Electronics, Page(s) 1086-1081, 2007
4. Y.K. Chin, W.M. Arshad, T. Bäckström & C. Sadarangani “Design of a Compact BLDC
motor for Transient Applications” Royal Institute of Technology (KTH) Department of
Electrical Engineering, 2008.
5. Dr. P.S.Bimbhra, Power Electronics, Khanna publishers, 2012.
6. Muhammad H.Rashid, Power Electronics: Circuits, Devices and applications, Pearson
Education, 2004
7. Gopal.K.Dubey, Fundamentals of Electrical Drives, Narosa Publishing House, 2002

Page | 38
Appendix

8051 PROGRAM
ORG 000
LJMP MAIN
ORG 0003
MOV A, #00H
BACK1: MOV P0, A
SETB P0.2
SETB P0.4
ACALL DELAY1
MOV P0,A
ACALL DDELAY
SETB P0.0
SETB P0.4
ACALL DELAY1
MOV P0,A
ACALL DDELAY
SETB P0.0
SETB P0.5
ACALL DELAY1
MOV P0,A

ACALL DDELAY
SETB P0.1
SETB P0.5
ACALL DELAY1
MOV P0,A
ACALL DDELAY
SETB P0.1
SETB P0.3
ACALL DELAY1
MOV P0,A
ACALL DDELAY
SETB P0.2
SETB P0.3
ACALL DELAY1
MOV P0,A
ACALL DDELAY
SJMP BACK1
ORG 0013
MOV A,#00H
BACK2: MOV P0,A

SETB P0.2
SETB P0.4
ACALL DELAY2
MOV P0,A
ACALL DDELAY
SETB P0.0
SETB P0.4
ACALL DELAY2
MOV P0,A
ACALL DDELAY
SETB P0.0
SETB P0.5
ACALL DELAY2
MOV P0,A
ACALL DDELAY
SETB P0.1
SETB P0.5
ACALL DELAY2
MOV P0,A
ACALL DDELAY
SETB P0.1

SETB P0.3
ACALL DELAY2
MOV P0,A
ACALL DDELAY
SETB P0.2
SETB P0.3
ACALL DELAY2
MOV P0,A
ACALL DDELAY
SJMP BACK2
MAIN: MOV IE,#85H
MOV A,#00H
BACK: MOV P0,A
SETB P0.2
SETB P0.4
ACALL DELAY
MOV P0,A
ACALL DDELAY

SETB P0.0
SETB P0.4
ACALL DELAY
MOV P0,A
ACALL DDELAY
SETB P0.0
SETB P0.5
ACALL DELAY
MOV P0,A
ACALL DDELAY
SETB P0.1
SETB P0.5
ACALL DELAY
MOV P0,A
ACALL DDELAY
SETB P0.1
SETB P0.3
ACALL DELAY
MOV P0,A
ACALL DDELAY
SETB P0.2

SETB P0.3
ACALL DELAY
MOV P0,A
ACALL DDELAY
SJMP BACK
DELAY :
MOV R2,#2
LOOP1: MOV R1,#255
LOOP2: MOV R0,#255
LOOP3: DJNZ R0,LOOP3
DJNZ R1,LOOP2
DJNZ R2,LOOP1
RET
DDELAY:
MOV R2,#3
LOOP:MOV R3,#255
HERE:DJNZ R3,HERE
DJNZ R2,LOOP
RET

DELAY1: MOV R2,#2
LOOP4: MOV R1,#200
LOOP5: MOV R0,#200
DJNZ R1,LOOP5
DJNZ R2,LOOP4
RET
DELAY2: MOV R2,#1
LOOP7: MOV R1,#150
LOOP8: MOV R0,#150
DJNZ R1,LOOP8
DJNZ R2,LOOP7
RET
END

Design and Fabrication of Three Phase BLDC Motor for Railway Application

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