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