Speed Control of DC Motor

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Department of Electrical Engineering HITEC University Taxila

8/22/2009

Speed Control Of DC Motor

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Group Supervisor:

Maj Aabis Raza

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Team Leader:

Nisar Ahmed Rana

Group Members:

M Shaban

Bilal Mushtaq

Muhammad Mohsin

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Acknowledgement

First of all, we will thank our Allah, The Most Beneficent The Most Merciful who made us able to complete this project.

No words are sufficient to express our gratitude to our loving parents for their exemplary patience, understanding and cooperation during the preparation of this book.

Those at Tank manufacturing factory, who had, contributed a great amount of time, talent and effort to move this project through its many phases in order To Design The Circuit For Controlling Speed Of Shunt Type 22kW DC Motor as you see it, include but are not limited to MD Tank factories, Maj. Abbis Raza and AFM Abdul Sittar. Without the help of staff of Tank manufacturing factories, we would probably be ___ well; we don’t want to think about that…

In completion of this project, we depend on expert input from our project adviser, MAJ. ABBIS RAZA who guided us in each step to make our project a better one.

We hope that you will find the circuit designed by us better than that of electronic circuit implemented by Chinese experts earlier, because we had used latest technology including Digital Display which will show the Speed of DC Motor.

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TO OUR GREAT NATIONAL HERO

DR. A. Q. KHAN

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Table of Content

1 Heavy Industries Taxila 4

2 Introduction 7 2.1 Background 8 2.2 Scope 8 2.3 Recommendation 9 2.4 Procedure 9 2.4.1 Circuit Designing 9 2.4.2 Programming of MCU 10 2.4.3 CCP Features of PIC 16F873 10 2.4.4 Circuit Simulation 11

2.4.5 Printed Circuit Board 12

2.4.6 Practical Implementation and Troubleshooting 12

3 Circuit Explanation 13

3.1 Control Voltage Input Circuit 14

3.2 Motor Derive Circuit 14

3.3 Clock Generator Circuit 14

3.4 LED Displaying Circuit 15

3.5 Power Supply Circuit 15

4 Parts Explanation 16

4.1 PIC16F873 MCU 16

4.2 3-Terminal Regulator 16

4.3 Transistor for MOSFET Derive 16

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4.5 Zener Diode 16

4.6 Diode Bridge Rectifier (W005G) 17

4.7 Resonator 17

4.8 Speed Control Rheostat 17

5 Printed Circuit Board 18

6 DC Motor 19

6.1 Magnetism 19

6.2 Magnetic Propulsion within a motor 21

6.3 Producing Mechanical Force 22

6.4 General Construction of DC Machine 22

6.5 Four Pole DC Motor 22

6.5.1 Armature Core or Stack 22

6.5.2 Armature Winding 23

6.5.3 Field Pole 23

6.5.4 Field coils 23

6.5.5 Yoke 23

6.5.6 Commutator 23

6.5.7 Brush and Brush Holders 23

6.5.8 Interpoles 23

6.5.9 Frame, End Bells, Shaft, and Bearings 24

6.5.10 Back end Front end 24

6.6 Shunt Wound - DC Operation Typical Speed - Torque Curve 24 6.7 Compound Wound - DC Operation Typical Speed - Torque Curve 24 6.8 Series Wound - DC Operation Typical Speed - Torque Curve 24 6.9 Permanent Magnet - DC Operation Typical Speed - Torque Curve 25

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6.10 Brush Shifting 25

6.11 Speed Torque Curve 26

6.12 Speed Regulation 26

6.13 Motor Starting 26

6.14 Losses 27

6.14.1 Friction and Windage 27

6.14.2 Armature Copper Losses 27

6.14.3 Field Copper Losses 27

6.14.4 Core Losses 27

6.15 Efficiency 27

6.16 Horse Power Basics 27

7 Conclusion 29 8 Appendices 30 8.1 Appendix A 30 8.2 Appendix B 33 8.3 Appendix C 35 8.4 Appendix D 36 9 References 38

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1 Heavy Industries Taxila

Heavy Industries Taxila is the backbone of Pakistan's engineering industry for the Pakistan Armed Forces, being a combination of multiple industries that has grown into a large military complex since 1980. It consists of six major production units and their support facilities, staffed by over 6500 highly skilled personnel. About 30% of the 6500 employees are uniformed military personnel.

HIT has facilities for overhaul, rebuild and progressive manufacturing of main battle tanks (MBT), armored recovery vehicles (ARV), armored personnel carriers (APC) and other armored vehicles of both eastern and western armored vehicles. HIT has developed and currently manufactures the Al-Khalid MBT.

Heavy Industries Taxila comprises various defense factories and facilities:

Heavy Rebuild Factory T-Series

It rebuilds and modernizes Tanks/Armored Recovery Vehicles of Chinese and Eastern European origin. With its vast experience and expertise, the factory has contributed immensely in achieving self-reliance with high quality and cost effective products exceeding productivity beyond its designated capacity.

Heavy Rebuild Factory M-Series

Heavy Rebuild Factory (M-Series) has the expertise of carrying out quality rebuild of tracked vehicles of US origin. The experience acquired over the last decade is reflected in the standards achieved. The factory specializes in M113 Series vehicles, which are given new life after rebuild strictly in accordance with OEM specifications.

APC Factory

The most famous of the M113 Family of vehicles are manufactured in this factory using state-of-the-art CNC machines CAD/CAM system and manufacturing technology unique in the world on MIG and TIG aluminum welding, radiographic inspection, chemical cleaning, coating and painting according to military specifications.

Gun Factory

The Gun factory has the capability of machining barrels ranging from 105 mm to 203 mm caliber. It has a longstanding experience in the manufacture of 105mm gun barrels for upgraded T-59 & T-69 tanks from steel of very high quality using Electro Slag Refining. Each barrel is auto-frottage and subjected to high precision work on state of the art machines.

Tank Factory

A modern outfit with latest tank manufacturing facilities which includes seven axis CNC machines for heavy duty flexible machining operations and a complete infrastructure for hull and turret manufacture.

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Development, Engineering Support and Components Manufacture (DESCOM)

This production facility has been established to provide engineering support to all the factories of HIT. Equipped with CNC machines, it undertakes manufacture of components, assemblies, tools, dies, gauges and arranges development of spare parts through the vendor industry. It also provides repair and maintenance support to machinery and equipment installed in HIT.

Evaluation, Training and Research Organization (ETRO)

This is a supporting organization which undertakes Quality Assurance of finished product of HIT ably assisted with modern quality assurance laboratories which test physical and chemical properties of production materials, Calibration facilities are available to ensure accuracy of tools and gauges used in rebuild and manufacturing processes.

Research and Development (R&D)

HIT has undertaken R&D projects on required basis wherein it has carried out successful R&D in the following areas:

 Tank design

 Tank modernization  Infantry fighting vehicles  Tank fire-control systems

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2 Introduction

Of late, solid state circuits using semiconductor diodes, transistors (MOSFET) and thyristors have become very popular for controlling the speed of AC as well as DC motors and are progressively replacing the traditional electric power control circuits based on thyratrons, ignitrons, mercury arc rectifier, magnetic amplifier and motor generator sets etc. As compared to electrical and electromechanical speed control system, the electronic methods have higher accuracy, greater reliability, quick response and also higher efficiency as there are no I2R loses and moving parts. Moreover, full four quadrant speed control is possible to meet precise high speed standards.

All electronic speed control circuits control the speed of motor by adjusting either i. Voltage applied to the motor armature or

ii. The field current or iii. Both of them

DC motors can run from DC supply if available or from AC supply after it has been converted into DC supply with the help of rectifier which can be either half wave or full wave and either controlled by varying conduction angle of the thyristors used or uncontrolled.

As stated above, the average output voltage of a thyristors controlled rectifier can be changed by changing its conduction angle and hence the armature voltage of the DC motor can be adjusted to control its speed.

When runs on a DC supply the armature DC voltage can be changed with the help of thyristors chopper circuit which can be made to interrupt DC supply at different rates to give different average values of DC voltage.

MOSFET are used to control the average DC power delivered to the motor by using Pulse Width Modulation technique. The PWM waveform will be generated from MCU and then after amplification is applied to the base of MOSFET. It will control the field current of motor to control its speed.[2]

2.1 Background

We were required to do a project during our internship in Tank Manufacturing factory. We have visited different shops and decided to make an electronic speed control for DC motor.

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The main reason behind it was we have just studied DC motors in our Electrical Machinery course in 4th _{semester. Also the electronic speed controls which are already in use have} older technology. We decided to make an electronic speed control by using a microcontroller. We also wanted to show the speed of motor on the LCD screen and also make some emergency protection switches. Due to our limited knowledge we were not able to complete all the proposed tasks but we have tried our best to complete them.

2.2 Scope

The characteristics of a shunt-wound motor give it very good speed regulation, and it is classified as a constant speed motor, even though the speed does slightly decrease as load is increased. Shunt-wound motors are used in industrial and automotive applications where precise control of speed and torque are required.

DC motors are widely used in industry in Robots, CNC Machines, Drilling Motors, helicopters; Food processors and grinders spin blades and Toaster ovens, tanks, heavy machinery, vehicles etc. They are also used in fans, turbines, drills, the wheels on electric cars, locomotives and conveyor belts. Also, in many vibrating or oscillating machines, an electric motor spins an irregular figure with more area on one side of the axle than the other, causing it to appear to be moving up and down

Sometimes the speed of the dc machines e.g. universal motors tend to go to destructive speeds, these speed may damage the equipment so speed control system is used in them. Speed control is used to set a desired torque to speed ratio for a desired load.

2.3 Recommendation

We have made the speed control system of a DC motor by using PWM pulse width modulation. There are some recommendations about the control system that are described briefly:

 This circuit is so simple as compared to the previous one so it’s easy to dig out the error in the circuit.

 The circuit is programmed by using the micro controller so there is more accuracy in this circuit.

 Previous circuits were very large and complex and this circuit is too simple to understand.

 Many DC motors are used in industry so we need their control system so it’s good to use this circuit because it’s more accurate and reliable.

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 In previous switch there was no protection i.e. when the speed increases from the required there was no switching off system but in this circuit we have the system that when the speed will increase from the required speed the circuit will control it.

2.4 Procedure

The whole project was divided into four portions:  Circuit Designing

 Programming of MCU  Circuit Simulation  PCB Designing

 Practical Implementation and Troubleshooting

2.4.1 Circuit Designing

We have consulted some books, searched on the internet, consulted with our teachers and discussed with our group supervisor. We have chosen different techniques but they were rejected due to their drawbacks. One of the main techniques was voltage chopper which chop the DC voltage into a required average voltage. Its average value can be adjusted by switching frequency for on time and off time of chopping MOSFET.

Another technique which can be implanted was the voltage controlled rectifier. It uses a three phase rectifier circuit implemented by using SCR. The firing angle of the SCR can be set by changing voltage at the gate terminal of SCR. When the voltage is increased SCR is fired at low input AC voltage when the voltage is decreased the SCR is fired at higher input AC voltage. So the average output voltage can be adjusted by changing the firing angle of SCR. Finally we have decided to use voltage controlled rectifier to control the speed of the motor.

2.4.2 Programming of MCU

Programming code of MCU is given in the Appendix it is also given in the CD as a soft copy.

2.4.3 CCP feature of PIC16F873

CCP is the initial of Capture/Compare/PWM (Pulse Width Modulation).

 Capture: this is the function to capture the 16 bits value of timer1 register when an event occurs on pin RC2/CCP1. This can be used for the measurement of the period time of the signal like the frequency counter and so on.

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 Compare: this is the function to compare constantly the 16 bits value of timer1 register against the CCPR1 register value. This is convenient when it makes interruption occur periodically.

 PWM: this is the function to make a periodic pulse generate. This function is used to control an external circuit with changing pulse duration (Duty).

The timer resource of the capture and compare is timer1 and the timer resource of PWM is timer2.

CCP1 and CCP2 can be worked at the same time. However, because they are using the same timer resources, the interaction occurs.

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CCP1 CCP2 Interaction of two CCP modules

Capture Capture Same TMR1 time-base.

The captured time value is different but it can be used at the same time.

Capture Compare Timer1 is cleared by compare operation._{So, it's better not to use the capture of CCP1.}

Capture PWM None.

Compare Capture Timer1 is cleared by compare operation._{So, it's better not to use the capture of CCP2.}

Compare Compare Timer1 is cleared by either compare operation. So, it isn't possible to use at the same time. Compare PWM None.

PWM Capture None. PWM Compare None.

PWM PWM The PWMs will have the same frequency and update rate.

CCP1 register is comprised of two 8 bits registers: CCPR1L for low byte and CCPR1H for high byte. The CCP1CON register controls the operation of CCP1. The special event trigger is generated by compare match and will reset Timer1.

CCP2 register is comprised of two 8 bits registers: CCPR2L for low byte and CCPR2H for high byte. The CCP2CON register controls the operation of CCP2. The special event trigger is generated by compare match and will reset Timer1 and start an A/D conversion if the A/D modules are enabled.

2.4.4 Circuit Simulation

A verity of software is available for simulation. We have used Proteus ISIS Schematic Capture because its library offers a wide range of components. It also has animated motors and LCD. It provides real time simulation of circuits. It also offers microcontroller simulation and some latest features. The software and Simulation files of all the circuits used are available in CD attached with the report.

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2.4.5 PCB Designing

Express PCB and Proteus ARES PCB Layout are tom main software to design PCB Layout. We have used ARES PCB Layout provided by Proteus to design the PCBs for our circuit. The PCB files and the software are provided in the attached CD.

2.4.6 Practical Implementation and Troubleshooting

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3 Circuits Explanation

Figure-3.1 Schematic Capture of Speed Control Circuit (Available in CD)

3.1 3.2 Control voltage input circuit

This is the circuit which inputs the control voltage which was created by the turning of the motor in PIC. The input voltage to PIC is converted by A/D converter. Changed voltage is used for the PWM function of the CCP to control the motor drive. At the circuit this time, a small motor is used as the generator to detect the number of rotations of the motor. The input voltage (the control voltage) to PIC is changed by the fluctuation of the number of rotations of the motor. The other way can be used to detect the number of rotations of the motor. It is needed to change control voltage to proportional to the number of rotations of the motor. PIC controls the drive electric current of the motor for the control voltage to become a regulation value. When the revolution of the motor slows down, i.e. control voltage goes down, the drive electric current of the motor is increased and number of rotations is raised. When the control voltage reaches a regulation value, an drive electric current at the point is held. Oppositely, when the number of rotations of the motor is high, i.e. the control voltage is high, the drive electric current of the motor is reduced and number

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of rotations is lowered. When the control voltage reaches a regulation value, an drive electric current at the point is held.

DB1 is used to make not conscious of the polarity of the motor. When never making a mistake in the connection, to use isn't necessary. When the voltage of the motor for the speed detection is small, it is better not to put.

D1 is used to protect PIC when the voltage of the detection motor is high. C1 is to make bypass the noise of the detection motor. VR1 is the variable resistor to set the number of rotations of the main motor. The input voltage of PIC becomes low when bringing VR1 close to the side 1 and PIC increases the drive electric current of the motor. That is, the revolution of the motor rises. The input voltage of PIC becomes high when bringing VR1 close to the side 3 and PIC reduces the drive electric current of the motor. That is, the revolution of the motor slows down.

3.3 Motor drive circuit

The PWM (Pulse Width Modulation) function of PIC is used for the electric current control to drive a motor.PWM can change the duty of the pulse to output into CCP1 by the data. When the time which is made the H level of the pulse of CCP1 is short, the time of ON (the L level) becomes long in TR2. That is, the drive electric current of the motor increases. Oppositely, when the H level time of the pulse of CCP1 is long, the ON time of TR2 becomes short and the drive electric current of the motor decreases.

The duty of the pulse of CCP1 is controlled in the voltage (the control voltage) which was taken in with the control voltage input circuit. When the control voltage is higher than the regulation value, the H level time of the CCP1 pulse is made long and the number of rotations of the motor is lowered. When the control voltage is lower than the regulation value, the H level time of the CCP1 pulse is made short and the number of rotations of the motor is raised.

I used N-channel MOS FET for the drive of the motor. The P-channel MOS FET can be used, too. In the case, the duty control of the CCP1 pulse becomes opposite. It becomes low-speed when the H level of the pulse is short and when long, it becomes high-low-speed. The way of connecting between the motor and the FET becomes opposite. In this case, the power of the transistor for the FET drive should be connected with the source terminal of P-FET. Because the output of the motor which was used this time is big, there is a gravity that the motor for the speed detection breaks. Therefore, an electric current is suppressed by the resistor to have put in series.

3.4 Clock generator circuit

We are using 10-MHz resonator.

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There is not directly relation but it is related with the taking-in period with control voltage, the period of the motor driving pulse to the number of rotations of the motor.

3.5 LED displaying circuit

LEDs are made to light up to monitor the drive situation of the motor. 3 bits of higher ranks of the control data of PWM are used for the lighting-up of LEDs. In the condition that a motor isn't driven, all LEDs are turned off. The number of the lighting-up is increased in the order from LED1 as the drive electric current increases. When the motor is in the maximum drive condition, all LEDs become lighting-up condition.

At the equipment this time, the LED of the bar type with seven LEDs is used. The circuit can control eight LEDs. However, at the equipment this time, LED1 isn't used and seven LEDs from LED2 to LED8 are used. An LED is lit up when RBx is H level.

3.6 Power supply circuit

3 terminal regulator is used to get the operating voltage for PIC.

The about 70-mA electric current flows when seven LEDs are lit up at the same time. I used a 1 A-type regulator for the safety.[3]

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4 Parts Explanation

4.1 PIC16F873 MCU

PIC16F873 MCU is used. The control of the drive electric current of the motor is done using the PWM function of the CCP. The voltage according to the number of rotations of the motor is taken in to the analog-to-digital converter and has the control of the drive electric current. This time, it is using a motor for the speed detection. Also, LEDs

for the monitor are lit up to know the situation of the motor drive. Data sheet for PIC16F873 is given in Appendix.

4.2 3 terminal regulator

This regulator is used to make the stable power of +5 V. Eight LEDs for the monitor sometimes light up at the same time.(This time, it is seven) So, when using a 100 mA-type regulator, little leeway occurs. This time, a 1A type is used for the safety.

4.3 Transistor for MOSFET drive

This transistor is used to drive MOS FET by the output of PIC. It is converting the output of PIC (0V to 5V) into the voltage to control an MOSFET (0V to 12V).

4.4 Power MOSFET

This is N channel MOS FET. The maximum continuous drain current is 60A. It can afford up to 228A pulsating current. When the FET is in the ON condition, the resistance between drain and source is 4 milli-ohm. So, the electric power loss when the 10-A electric current flows in the ON condition is 0.4 W.

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4.5 Zener Diode

The voltage which is applied to the terminal of PIC is a maximum of +5V. This diode prevents the destruction of PIC when the speed detection voltage of the motor exceeds 5V. When more than +5V voltage be applied never from outside, it is unnecessary.

4.6 Diode Bridge for speed detection voltage polarity

protection

We put the silicon diode bridge not to be in the problem even if it connected

the pole of the motor for the speed detection oppositely. When never making a mistake in the connection, it is unnecessary.

4.7 Resonator

We have used a 10MH Crystal to produce resonance frequency. When changing the frequency of resonator, the value with all kinds on the software must be changed.

4.8 Speed Control Rheostat

We have used a speed control rheostat to control the speed of the motor. It becomes low-speed when turning to the left and it becomes high-low-speed when turning to the right.

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5 Printed Circuit Board

PCB layout of the circuit was made in ARES by Proteus. A copy of the PCB file and software is included in the CD.

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6 DC Motor

It has been said that if the Ancient Romans, with their advanced civilization and knowledge of the sciences, had been able to develop a steam motor, the course of history would have been much different. The development of the electric motor in modern times has indicated the truth in this theory. The development of the electric motor has given us the most efficient and effective means to do work known to man. Because of the electric motor we have been able to greatly reduce the painstaking toil of man's survival and have been able to build a civilization which is now reaching to the stars. The electric motor is a simple device in principle. It converts electric energy into mechanical energy. Over the years, electric motors have changed substantially in design; however the basic principles have remained the same.

6.1 Magnetism

We all know that a permanent magnet will attract and hold metal objects when the object is near or in contact with the magnet. The permanent magnet is able to do this because of its inherent magnetic force which is referred to as a "magnetic field".

Figure-6.1 The lines of flux of a magnetic field travel from the N-pole to the S-pole.

These lines of flux help us to visualize the magnetic field of any magnet even though they only represent invisible phenomena. The number of lines of flux varies from one magnetic field to another. The stronger the magnetic field, the greater the number of lines of flux which are drawn to represent the magnetic field. The lines of flux are drawn with a direction indicated since we should visualize these lines and the magnetic field they represent as having a distinct movement from N-pole to S-pole as shown in Figure-6.1. Another but

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similar type of magnetic field is produced around an electrical conductor when an electric current is passed through the conductor as shown in Figure6.2

Figure-6.2 The flow of electrical current in a conductor sets up concentric lines of magnetic flux around the conductor.

These lines of flux define the magnetic field and are in the form of concentric circles around the wire. Some of you may remember the old "Left Hand Rule" as shown in Figure-6.2. The rule states that if you point the thumb of your left hand in the direction of the current, your fingers will point in the direction of the magnetic field.

Figure-6.3 The magnetic lines around a current carrying conductor leave from the N-pole and re-enter at the S-pole.

When the wire is shaped into a coil as shown in Figure-6.3, all the individual flux lines produced by each section of wire join together to form one large magnetic field around the total coil. As with the permanent magnet, these flux lines leave the north of the coil and

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re-enter the coil at its south pole. The magnetic field of a wire coil is much greater and more localized than the magnetic field around the plain conductor before being formed into a coil. This magnetic field around the coil can be strengthened even more by placing a core of iron or similar metal in the center of the core. The metal core presents less resistance to the lines of flux than the air, thereby causing the field strength to increase.

6.2 Magnetic Propulsion Within A Motor

The basic principle of all motors can easily be shown using two electromagnets and a permanent magnet. Current is passed through coil no. 1 in such a direction that a north pole is established and through coil no. 2 in such a direction that a south pole is established. A permanent magnet with a north and South Pole is the moving part of this simple motor. In Figure 5-a, the north pole of the permanent magnet is opposite the North Pole of the electromagnet. Similarly, the south poles are opposite each other. Like magnetic poles repel each other, causing the movable permanent magnet to begin to turn. After it turns part way around, the force of attraction between the unlike poles becomes strong enough to keep the permanent magnet rotating. The rotating magnet continues to turn until the unlike poles are lined up. At this point the rotor would normally stop because of the attraction between the unlike poles. (Figure-2.4 B)

If, however, the direction of currents in the electromagnetic coils was suddenly reversed, thereby reversing the polarity of the two coils, then the poles would again be opposites and repel each other. (Figure-2.4 C). The movable permanent magnet would then continue to rotate. If the current direction in the electromagnetic coils was changed every time the magnet turned 180 degrees or halfway around, then the magnet would continue to rotate. This simple device is a motor in its simplest form. An actual motor is more complex than the simple device shown above, but the principle is the same.

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6.3 Producing Mechanical Force

As in the generator, the motor has a definite relationship between the direction of the magnetic flux, the direction of motion of the conductor or force, and the direction of the applied voltage or current.

Since the motor is the reverse of the generator, Fleming's left hand rule can be used. If the thumb and first two fingers of the left hand are extended at right angles to one another, the thumb will indicate the direction of motion, the forefinger will indicate the direction of the magnetic field, and the middle finger will indicate the direction of current. In either the motor or generator, if the directions of any two factors are known, the third can be easily determined.

6.4 General Construction of DC Machines

A typical DC generator or motor usually consists of: 1. An armature core 2. An air gap 3. Poles 4. A yoke 5. An armature winding 6. A field winding 7. Brushes 8. A commutator 9. A frame 10. End bells 11. Bearings 12. Brush supports 13. A shaft

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6.5 Four Pole DC Motor

6.5.1 Armature Core or Stack

The armature stack is made up thin magnetic steel laminations stamped from sheet steel with a blanking die. Slots are punched in the lamination with a slot die. Sometimes these two operations are done as one. The laminations are welded, riveted, bolted or bonded together.

6.5.2 Armature Winding

The armature winding is the winding, which fits in the armature slots and is eventually connected to the commutator. It either generates or receives the voltage depending on whether the unit is a generator or motor. The armature winding usually consists of copper wire, either round or rectangular and is insulated from the armature stack.

6.5.3 Field Poles

The pole cores can be made from solid steel castings or from laminations. At the air gap, the pole usually fans out into what is known as a pole head or pole shoe. This is done to reduce the reluctance of the air gap. Normally the field coils are formed and placed on the pole cores and then the whole assembly is mounted to the yoke.

6.5.4 Field Coils

The field coils are those windings, which are located on the poles and set up the magnetic fields in the machine. They also usually consist of copper wire are insulated from the poles. The field coils may be either shunt windings (in parallel with the armature winding) or series windings (in series with the armature winding) or a combination of both.

6.5.5 Yoke

The yoke is a circular steel ring, which supports the field, poles mechanically and provides the necessary magnetic path between the poles. The yoke can be solid or laminated. In many DC machines, the yoke also serves as the frame.

6.5.6 Commutator

The commutator is the mechanical rectifier, which changes the AC voltage of the rotating conductors to DC voltage. It consists of a number of segments normally equal to the number of slots. The segments or commutator bars are made of silver bearing copper and are separated from each other by mica insulation.

6.5.7 Brushes and Brush Holders

Brushes conduct the current from the commutator to the external circuit. There are many types of brushes. A brush holder is usually a metal box that is rectangular in shape. The brush holder has a spring that holds the brush in contact with the commutator. Each brush usually has a flexible copper shunt or pigtail, which extends to the lead wires. Often, the entire brush assembly is insulated from the frame and is made movable as a unit about the commutator to allow for adjustment.

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6.5.8 Interpoles

Interpoles are similar to the main field poles and located on the yoke between the main field poles. They have windings in series with the armature winding. Interpoles have the function of reducing the armature reaction effect in the

commutating zone. They eliminate the need to shift the brush assembly.

6.5.9 Frame, End Bells, Shaft, and Bearings

The frame and end bells are usually steel, aluminum or magnesium castings used to enclose and support the basic machine parts. The armature is mounted on a steel shaft, which is supported between two bearings. The bearings are sleeve, ball or roller type. They are normally lubricated by grease or oil.

6.5.10 Back End, Front End

The load end of the motor is the Back End. The opposite load end, most often the commutator end, is the Front End of the motor.

6.6 Shunt Wound - DC Operation Typical

Speed - Torque Curve

Shunt wound motors, with the armature shunted across the field, offer relatively flat speed-torque characteristics. Combined with inherently controlled no-load speed, this provides good speed regulation over wide load ranges. While the starting torque is comparatively lower than the other DC winding types, shunt wound motors offer simplified control for reversing service.

6.7 Compound Wound - DC Operation Typical Speed - Torque Curve

Compound wound (stabilized shunt) motors utilize a field winding in series with the armature in addition to the shunt field to obtain a compromise in performance between a series and shunt type motor. This type offers a combination of good starting torque and speed stability. Standard compounding is about 12%. Heavier compounding of up to 40 to 50% can be supplied for special high starting torque applications, such as hoists and cranes.

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Series wound motors have the armature connected in series with the field. While it offers very high starting torque and good torque output per ampere, the series motor has poor speed regulation. Speed of DC series motors is generally limited to 5000 rpm and below. Series motors should be avoided in applications where they are likely to lose their load because of their tendency to "run away" under no-load conditions. These are generally used on crane and hoist applications.

6.9 Permanent Magnet - DC Operation Typical Speed - Torque Curve

Permanent magnet motors have no wound field and a

conventional wound armature with commutator and brushes. This motor has excellent starting torques, with speed regulation not as good as compound motors. However, the speed regulation can be improved with various designs, with corresponding lower rated torques for a given frame. Because of permanent field, motor losses is less with better operating efficiencies. These motors can be dynamically braked and reversed at some low armature voltage (10%) but should not be plug reversed with full armature voltage. Reversing current can be no higher than the locked armature current.

6.10 Brush Shifting

One method of reducing the arcing due to non-linear commutation is to shift the brushes away from the geometrical neutral position. Then commutation will occur when the applicable coil is under the influence of a weak magnetic field that will generate a voltage in the coil, which opposes the induced voltage due to current change. Therefore, this new voltage will assist rather than hinder the current reversal. In a generator, it is necessary to shift the brushes forward in the direction of rotation for good commutation. This is true because the current flow through the conductors is in the same direction as the voltage and, it commutation is delayed until the coil sides are under the

next pole, it will be assisted by the current reversing voltage. In a motor, it is necessary to shift the brushes against the direction of rotation because current flow is in opposition to the induced voltage. The amount of shift necessary depends on the load so a given shift will not be satisfactory for all loads. One effect of shifting brushes is that a demagnetization component of armature reaction is introduced. In other words, when the brushes are shifted, the armature reaction will not only distort the main field flux but it will also directly oppose the main field. This will

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result in a reduction of the field flux. Another effect is that if the brushes are shifted far enough, it is possible to reduce the number of effective turns because there will be voltages in opposition to each other between two brushes.

6.11 Speed Torque Curves

Speed torque curves for the three forms of excitation are shown in Figures given above. In a shunt excited motor, the change in speed is slight and, therefore, it is considered a constant speed motor. Also, the field flux is nearly constant in a shunt motor and the torque varies almost directly with armature current.

In a series motor the drop in speed with increased torque is much greater. This is due to the fact that the field flux increases with increased current, thus tending to prevent the reduction in back EMF that is being caused by the reduction in speed. The field flux varies in a series motor and the torque varies as the square of the armature current until saturation is reached. Upon reaching saturation, the curve tends to approach the straight line trend of the shunt motor. The no load speed of a series motor is usually too high for safety and, therefore, it should never be operated without sufficient load.

A compound motor has a speed torque characteristic which lies between a shunt and series motor.

6.12 Speed Regulation

Speed regulation is the change in speed with the change in load torque, other conditions being constant. A motor has good regulation if the change between the no load speed and full load speed is small.

A shunt motor has good speed regulation while a series motor has poor speed regulation. For some applications such as cranes or hoists, the series motor has an advantage since it results in the more deliberate movement of heavier loads. Also, the slowing down of the series motor is better for heavy starting loads. However, for many applications the shunt motor is preferred.

6.13 Motor Starting

When the armature is not rotating, the back EMF is zero and the total applied voltage is available for sending current through the armature. Since the armature resistance is low, an enormous current would flow if voltage were applied under this condition. Therefore, it is necessary to insert an additional resistance in series with the armature until a satisfactory speed is reached where the back EMF will take over to limit the current input.

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6.14 Losses

6.14.1 Friction and Windage

These losses include bearing friction, brush friction, and windage. They are also known as mechanical losses. They are constant at a given speed but vary with changes in speed. Power losses due to friction increase as the square of the speed and those due to windage increase as the cube of the speed.

6.14.2 Armature Copper Losses

These are the I2 R losses of the armature circuit, which includes the armature winding, commutator, and brushes. They vary directly with the resistance and as the square of the currents.

6.14.3 Field Copper Losses

These are the I2 R losses of the field circuit which can include the shunt field winding, series field winding, interpole windings and any shunts used in connection with these windings. They vary directly with the resistance and as the square of the currents.

6.14.4 Core Losses

These are the hysteresis and eddy current losses in the armature. With the continual change of direction of flux in the armature iron, an expenditure of energy is required to carry the iron through a complete hysteresis loop. This is the hysteresis loss. Also since the iron is a conductor and revolving in a magnetic field, a voltage will be generated. This, in turn, will result in small circulating currents known as eddy currents. If a solid core were used for the armature, the eddy current losses would be high. They are reduced by using thin laminations, which are insulated from each other. Hysteresis and eddy current losses vary with flux density and speed.

6.15 Efficiency

For generations or motors, the efficiency is equal to the output divided by the input. However, in a generator, the input is mechanical while the output is electrical. In a motor the opposite is true, therefore:

6.16 Horsepower Basics

In 18th century England, coal was feeding the industrial revolution and Thomas Newcomen invented a steam driven engine that was used to pump water from coal mines. It was a Scott

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however, by the name of James Watt, who in 1769 improved the steam engine making it truly workable and practical. In his attempt to sell his new steam engines, the first question coal mine owners asked was "can your engine out work one of my horses?" Watt didn't know since he didn't know how much work a horse could do. To find out, Watt and his partner bought a few average size horses and measured their work. They found that the average horse worked at the rate of 22,000 foot pounds per minute. Watt decided, for some unknown reason, to add 50% to this figure and rate the average horse at 33,000 foot pounds per minute.

What's important is that there is now a system in place for measuring the rate of doing work. And there is a unit of power, horsepower.

If steam engines had been developed someplace else in the world, where the horse was not the beast of burden, we might be rating motors in oxen power or camel power. Today, motors are also rated in Watts output.

Horsepower as defined by Watt is the same for AC and DC motors, gasoline engines, dog sleds, etc.

Horsepower and Electric Motors

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7 Conclusion

Our internship project was that to design a speed control circuit for a DC Motor. The simulations indicate that this circuit is very easy to implement, in this circuit. Fewer components are used due to which troubleshooting is made easy. As MCU is used in this circuit so it is more precise, accurate and reliable.

That’s why this circuit is clearly the better design. This design requires minimal cost to implement the circuit, it is relatively easy to debug and its maintenance is easy due to simple and short design. In addition, it is cheaper to build and more durable.

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8 Appendices

Appendix A

Programming Code of MCU

include p16f873.inc

__config _hs_osc & _wdt_off & _pwrte_on & _lvp_off errorlevel -302 ;Suppress bank warning

;**************** Label Definition ******************** speed equ d'8' ;Reference speed (5x8/256=0.156V) change equ d'1' ;Change value (2mV/ms)

led equ h'20' ;LED control data save area

;**************** Program Start *********************** org 0 ;Reset Vector

goto init

org 4 ;Interrupt Vector goto int

;**************** Initial Process ********************* init

;*** Port initialization

bsf status,rp0 ;Change to Bank1 movlw b'00000001' ;AN0 to input mode movwf trisa ;Set TRISA register clrf trisb ;Set TRISB to uotput mode clrf trisc ;Set TRISC to output mode bcf status,rp0 ;Change to Bank0 ;*** A/D converter initialization

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movlw b'10000001' ;ADCS=10 CHS=AN0 ADON=ON movwf adcon0 ;Set ADCON0 register

bsf status,rp0 ;Change to Bank1 movlw b'00001110' ;ADFM=0 PCFG=1110 movwf adcon1 ;Set ADCON1 register bcf status,rp0 ;Change to Bank0 ;*** PWM initialization

clrf tmr2 ;Clear TMR2 register movlw b'11111111' ;Max duty (low speed) movwf ccpr1l ;Set CCPR1L register bsf status,rp0 ;Change to Bank1

movlw d'255' ;Period=1638.4usec(610Hz) movwf pr2 ;Set PR2 register

bcf status,rp0 ;Change to Bank0

movlw b'00000110' ;Pst=1:1 TMR2=ON Pre=1:16 movwf t2con ;Set T2CON register

movlw b'00001100' ;CCP1XY=0 CCP1M=1100(PWM) movwf ccp1con ;Set CCP1CON register

;*** Compare mode initialization

clrf tmr1h ;Clear TMR1H register clrf tmr1l ;Clear TMR1L register movlw h'61' ;H'61A8'=25000 movwf ccpr2h ;Set CCPR2H register movlw h'a8' ;25000*0.4usec = 10msec movwf ccpr2l ;Set CCPR2L register

movlw b'00000001' ;Pre=1:1 TMR1=Int TMR1=ON movwf t1con ;Set T1CON register

movlw b'00001011' ;CCP2M=1011(Compare) movwf ccp2con ;Set CCP2CON register

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;*** Interruption control

bsf status,rp0 ;Change to Bank1 movlw b'00000001' ;CCP2IE=Enable movwf pie2 ;Set PIE2 register bcf status,rp0 ;Change to Bank0 movlw b'11000000' ;GIE=ON PEIE=ON movwf intcon ;Set INTCON register wait

goto $ ;Interruption wait

;*************** Interruption Process ***************** int

clrf pir2 ;Clear interruption flag ad_check

btfsc adcon0,go ;A/D convert end ? goto ad_check ;No. Again

movfw adresh ;Read ADRESH register sublw speed ;Ref speed - Detect speed btfsc status,c ;Reference < Detect ? goto check1 ;No. Jump to > or = check ; control to low speed

---movfw ccpr1l ;Read CCPR1L register addlw change ;Change value + CCPR1L btfss status,c ;Overflow ?

movwf ccpr1l ;No. Write CCPR1L goto led_cont ;Jump to LED control check1

btfsc status,z ;Reference = Detect ? goto led_cont ;Yes. Jump to LED control ; control to fast speed

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---movlw change ;Set change value subwf ccpr1l,f ;CCPR1L - Change value btfsc status,c ;Underflow ?

goto led_cont ;Jump to LED control clrf ccpr1l ;Set fastest speed

;**************** LED control Process ****************** led_cont

comf ccpr1l,w ;Complement CCPR1L bit movwf led ;Save LED data

movlw b'00010000' ;Set compare data subwf led,w ;LED - data

btfsc status,c ;Under ? goto led1 ;No.

movlw b'00000000' ;Set LED control data goto int_end ;Jump to interrupt end led1 movlw b'00100000' ;Set compare data

subwf led,w ;LED - data btfsc status,c ;Under ? goto led2 ;No.

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btfsc status,c ;Under ? goto led4 ;No.

movlw b'01111111' ;Set LED control data goto int_end ;Jump to interrupt end led8 movlw b'11111111' ;Set LED control data

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;************ END of Interruption Process ************** int_end

movwf portb ;Set PROTB retfie

;******************************************************** ; END of DC motor speed controller

;******************************************************** End

Appendix B

PIC16F87XA Data Sheet

28 Pin Enhanced Flash Microcontrollers

High-Performance RISC CPU

Only 35 single-word instructions to learn

All single-cycle instructions except for program branches, which are two-cycle Operating speed: DC – 20 MHz clock input DC – 200 ns instruction cycle

Up to 8K x 14 words of Flash Program Memory, Up to 368 x 8 bytes of Data Memory (RAM), Up to 256 x 8 bytes of EEPROM Data Memory

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Pinout compatible to other 28-pin or 40/44-pin PIC16CXXX and PIC16FXXX microcontrollers

Peripheral Features

Timer0: 8-bit timer/counter with 8-bit prescaler

Timer1: 16-bit timer/counter with prescaler, can be incremented during Sleep via external crystal/clock

Timer2: 8-bit timer/counter with 8-bit period register, prescaler and postscaler Two Capture, Compare, PWM modules

Capture is 16-bit, max. Resolution is 12.5 ns Compare is 16-bit, max. Resolution is 200 ns PWM max. Resolution is 10-bit

Synchronous Serial Port (SSP) with SPI™ Master mode) and I2C™(Master/Slave)

Universal Synchronous Asynchronous Receiver Transmitter (USART/SCI) with 9-bit address detection Parallel Slave Port (PSP) – 8 bits wide with external RD, WR and CS controls (40/44-pin only)

Brown-out detection circuitry for Brown-out Reset (BOR)

Analog Features

10-bit, up to 8-channel Analog-to-Digital Converter (A/D) Brown-out Reset (BOR)

Analog Comparator module with: Two analog comparators

Programmable on-chip voltage reference (VREF) module

Programmable input multiplexing from device inputs and internal voltage reference Comparator outputs are externally accessible

Special Microcontroller Features

100,000 erase/write cycle Enhanced Flash program memory typical 1,000,000 erase/write cycle Data EEPROM memory typical

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Self-reprogrammable under software control In-Circuit Serial Programming™(ICSP™) via two pins Single-supply 5V In-Circuit Serial Programming

Watchdog Timer (WDT) with its own on-chip RC oscillator for reliable operation Programmable code protection

Power saving Sleep mode Selectable oscillator options In-Circuit Debug (ICD) via two pins

CMOS Technology

Low-power, high-speed Flash/EEPROM technology Fully static design

Wide operating voltage range (2.0V to 5.5V) Commercial and Industrial temperature ranges Low-power consumption

Appendix C

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Appendix D

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9 References

[1]Web:http://www.wikipedia.org

[2] Book “Electrical Technology” by “BL Theraja” and “AK Theraja”, 23rd_{Edition, Volume 1} [3] Article: “Reliance Basic Motor Theory”, By “Baldor Electric Company”

Some Other Resources

Book: “Electronic Devices” by “Thomas L Floyd”, 4th_Edition

Web:http://downloads.labcenter.co.uk

Web:http://www.google.com

Web:http://www.images.google.com