speed control of dc motor

Tank Manufacturing FactoryHeavy Industries Taxila

Speed Control Of DC Motor

Grou

Ma

Te

NisaGro

p Supervisor:

j Aabis Raza

Department of Electrical Engineering

HITEC University Taxila

Bi

Muha

am Leader:

r Ahmed Ranaup Members:

M Shabanlal Mushtaqmmad Mohsin

8/22/2009

August 22, 2009 [SPEED CONTROL OF DC MOTOR]

2 Internship Report by (HITEC University) Students| Heavy Industries Taxila

AcknowledgementFirst of all, we will thank our Allah, The Most Beneficent The Most Merciful who made us able tocomplete 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 tomove this project through its many phases in order To Design The Circuit For Controlling Speed Of ShuntType 22kW DC Motor as you see it, include but are not limited to MD Tank factories, Maj. Abbis Razaand 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 RAZAwho 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 implementedby Chinese experts earlier, because we had used latest technology including Digital Display which willshow the Speed of DC Motor.

Thanks again to all of you.



TO OUR GREAT NATIONAL HERO

DR. A. Q. KHAN



Table of Content1 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

4.4 Power MOSFET 16



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



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



1 Heavy Industries TaxilaHeavy Industries Taxila is the backbone of Pakistan's engineering industry for the Pakistan ArmedForces, being a combination of multiple industries that has grown into a large military complex since1980. It consists of six major production units and their support facilities, staffed by over 6500 highlyskilled 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 botheastern and western armored vehicles. HIT has developed and currently manufactures the Al-KhalidMBT.

Heavy Industries Taxila comprises various defense factories and facilities:

Heavy Rebuild Factory T-SeriesIt 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-reliancewith high quality and cost effective products exceeding productivity beyond its designated capacity.

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

APC FactoryThe most famous of the M113 Family of vehicles are manufactured in this factory using state-of-the-artCNC machines CAD/CAM system and manufacturing technology unique in the world on MIG and TIGaluminum welding, radiographic inspection, chemical cleaning, coating and painting according tomilitary specifications.

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

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



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, gaugesand arranges development of spare parts through the vendor industry. It also provides repair andmaintenance 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 ablyassisted with modern quality assurance laboratories which test physical and chemical properties ofproduction materials, Calibration facilities are available to ensure accuracy of tools and gauges used inrebuild 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 thefollowing areas:

Tank design

Tank modernization

Infantry fighting vehicles

Tank fire-control systems

[1]



2 IntroductionOf late, solid state circuits using semiconductor diodes, transistors (MOSFET) and thyristorshave become very popular for controlling the speed of AC as well as DC motors and areprogressively replacing the traditional electric power control circuits based on thyratrons,ignitrons, mercury arc rectifier, magnetic amplifier and motor generator sets etc. Ascompared to electrical and electromechanical speed control system, the electronic methodshave higher accuracy, greater reliability, quick response and also higher efficiency as thereare no I2R loses and moving parts. Moreover, full four quadrant speed control is possible tomeet 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 convertedinto DC supply with the help of rectifier which can be either half wave or full wave andeither controlled by varying conduction angle of the thyristors used or uncontrolled.

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

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

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

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



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

2.2 ScopeThe characteristics of a shunt-wound motor give it very good speed regulation, and it isclassified as a constant speed motor, even though the speed does slightly decrease asload is increased. Shunt-wound motors are used in industrial and automotive applicationswhere 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, heavymachinery, vehicles etc. They are also used in fans, turbines, drills, the wheels on electriccars, locomotives and conveyor belts. Also, in many vibrating or oscillating machines, anelectric motor spins an irregular figure with more area on one side of the axle than theother, 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 destructivespeeds, 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 RecommendationWe have made the speed control system of a DC motor by using PWM pulse widthmodulation. There are some recommendations about the control system that are describedbriefly:

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

The circuit is programmed by using the micro controller so there is more accuracy inthis circuit.

Previous circuits were very large and complex and this circuit is too simple tounderstand.

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



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

2.4 ProcedureThe whole project was divided into four portions:

Circuit Designing

Programming of MCU

Circuit Simulation

PCB Designing

Practical Implementation and Troubleshooting

2.4.1 Circuit DesigningWe have consulted some books, searched on the internet, consulted with our teachers anddiscussed with our group supervisor. We have chosen different techniques but they wererejected due to their drawbacks. One of the main techniques was voltage chopper whichchop the DC voltage into a required average voltage. Its average value can be adjusted byswitching frequency for on time and off time of chopping MOSFET.

Another technique which can be implanted was the voltage controlled rectifier. It uses athree phase rectifier circuit implemented by using SCR. The firing angle of the SCR can be setby changing voltage at the gate terminal of SCR. When the voltage is increased SCR is firedat low input AC voltage when the voltage is decreased the SCR is fired at higher input ACvoltage. 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 MCUProgramming 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 PIC16F873CCP 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 anevent occurs on pin RC2/CCP1. This can be used for the measurement of the periodtime of the signal like the frequency counter and so on.



Compare: this is the function to compare constantly the 16 bits value of timer1register against the CCPR1 register value. This is convenient when it makesinterruption occur periodically.

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

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

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



CCP1 CCP2 Interaction of two CCP modules

Capture CaptureSame TMR1 time-base.The captured time value is different but it can be used at the same time.

Capture CompareTimer1 is cleared by compare operation.So, it's better not to use the capture of CCP1.

Capture PWM None.

Compare CaptureTimer1 is cleared by compare operation.So, it's better not to use the capture of CCP2.

Compare CompareTimer1 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 highbyte. The CCP1CON register controls the operation of CCP1. The special event trigger isgenerated by compare match and will reset Timer1.

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

2.4.4 Circuit SimulationA verity of software is available for simulation. We have used Proteus ISIS SchematicCapture because its library offers a wide range of components. It also has animated motorsand LCD. It provides real time simulation of circuits. It also offers microcontroller simulationand some latest features. The software and Simulation files of all the circuits used areavailable in CD attached with the report.



2.4.5 PCB DesigningExpress PCB and Proteus ARES PCB Layout are tom main software to design PCB Layout. Wehave used ARES PCB Layout provided by Proteus to design the PCBs for our circuit. The PCBfiles and the software are provided in the attached CD.

2.4.6 Practical Implementation and TroubleshootingDue to the shortage of time we were not able to practically implement and test the circuit.



3 Circuits Explanation

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

3.1

3.2 Control voltage input circuitThis is the circuit which inputs the control voltage which was created by the turning of themotor in PIC. The input voltage to PIC is converted by A/D converter. Changed voltage isused for the PWM function of the CCP to control the motor drive. At the circuit this time, asmall motor is used as the generator to detect the number of rotations of the motor. Theinput voltage (the control voltage) to PIC is changed by the fluctuation of the number ofrotations of the motor. The other way can be used to detect the number of rotations of themotor. It is needed to change control voltage to proportional to the number of rotations ofthe motor. PIC controls the drive electric current of the motor for the control voltage tobecome a regulation value. When the revolution of the motor slows down, i.e. controlvoltage goes down, the drive electric current of the motor is increased and number ofrotations is raised. When the control voltage reaches a regulation value, an drive electriccurrent 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



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

DB1 is used to make not conscious of the polarity of the motor. When never making amistake in the connection, to use isn't necessary. When the voltage of the motor for thespeed 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 makebypass the noise of the detection motor. VR1 is the variable resistor to set the number ofrotations of the main motor. The input voltage of PIC becomes low when bringing VR1 closeto the side 1 and PIC increases the drive electric current of the motor. That is, the revolutionof the motor rises. The input voltage of PIC becomes high when bringing VR1 close to theside 3 and PIC reduces the drive electric current of the motor. That is, the revolution of themotor slows down.

3.3 Motor drive circuitThe PWM (Pulse Width Modulation) function of PIC is used for the electric current control todrive a motor.PWM can change the duty of the pulse to output into CCP1 by the data. Whenthe 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 andthe drive electric current of the motor decreases.

The duty of the pulse of CCP1 is controlled in the voltage (the control voltage) which wastaken in with the control voltage input circuit. When the control voltage is higher than theregulation value, the H level time of the CCP1 pulse is made long and the number ofrotations of the motor is lowered. When the control voltage is lower than the regulationvalue, the H level time of the CCP1 pulse is made short and the number of rotations of themotor 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-speed. The wayof connecting between the motor and the FET becomes opposite. In this case, the power ofthe 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 themotor for the speed detection breaks. Therefore, an electric current is suppressed by theresistor to have put in series.

3.4 Clock generator circuitWe are using 10-MHz resonator.



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 circuitLEDs are made to light up to monitor the drive situation of the motor. 3 bits of higher ranksof the control data of PWM are used for the lighting-up of LEDs. In the condition that amotor isn't driven, all LEDs are turned off. The number of the lighting-up is increased in theorder from LED1 as the drive electric current increases. When the motor is in the maximumdrive 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 cancontrol eight LEDs. However, at the equipment this time, LED1 isn't used and seven LEDsfrom LED2 to LED8 are used. An LED is lit up when RBx is H level.

3.6 Power supply circuit3 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 useda 1 A-type regulator for the safety.[3]



4 Parts Explanation

4.1 PIC16F873 MCUPIC16F873 MCU is used. The control of the driveelectric current of the motor is done using thePWM function of the CCP. The voltage accordingto the number of rotations of the motor is takenin to the analog-to-digital converter and has thecontrol of the drive electric current. This time, it isusing a motor for the speed detection. Also, LEDsfor 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 regulatorThis regulator is used to make the stable power of +5 V. Eight LEDs for the monitorsometimes light up at the same time.(This time, it is seven) So, when using a 100 mA-typeregulator, little leeway occurs. This time, a 1A type is used for the safety.

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

4.4 Power MOSFETThis is N channel MOS FET. The maximum continuous drain current is 60A. It can afford upto 228A pulsating current. When the FET is in the ON condition, the resistance betweendrain and source is 4 milli-ohm. So, the electric power loss when the 10-A electric currentflows in the ON condition is 0.4 W.

The datasheet for Power MOSFET is given in Appendix.



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

4.6 Diode Bridge for speed detection voltage polarityprotectionWe put the silicon diode bridge not to be in the problem even if it connectedthe pole of the motor for the speed detection oppositely. When never making a mistake inthe connection, it is unnecessary.

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

4.8 Speed Control RheostatWe 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-speed when turning to the right.



5 Printed Circuit BoardPCB layout of the circuit was made in ARES by Proteus. A copy of the PCB file and software isincluded in the CD.

A 3D layout of the PCB generated by ARES is also given below.



6 DC MotorIt has been said that if the Ancient Romans, with their advanced civilization and knowledge of thesciences, had been able to develop a steam motor, the course of history would have been muchdifferent. 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 workknown to man. Because of the electric motor we have been able to greatly reduce the painstaking toil ofman's survival and have been able to build a civilization which is now reaching to the stars. The electricmotor 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 thesame.

6.1 MagnetismWe all know that a permanent magnet will attract and hold metal objects when the object isnear or in contact with the magnet. The permanent magnet is able to do this because of itsinherent 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 theyonly represent invisible phenomena. The number of lines of flux varies from one magneticfield to another. The stronger the magnetic field, the greater the number of lines of fluxwhich are drawn to represent the magnetic field. The lines of flux are drawn with a directionindicated since we should visualize these lines and the magnetic field they represent ashaving a distinct movement from N-pole to S-pole as shown in Figure-6.1. Another but



similar type of magnetic field is produced around an electrical conductor when an electriccurrent 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 magneticflux around the conductor.

These lines of flux define the magnetic field and are in the form of concentric circles aroundthe wire. Some of you may remember the old "Left Hand Rule" as shown in Figure-6.2. Therule states that if you point the thumb of your left hand in the direction of the current, yourfingers 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 andre-enter at the S-pole.

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



enter the coil at its south pole. The magnetic field of a wire coil is much greater and morelocalized 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 ironor similar metal in the center of the core. The metal core presents less resistance to the linesof flux than the air, thereby causing the field strength to increase.

6.2 Magnetic Propulsion Within A MotorThe basic principle of all motors can easily be shown using two electromagnets and apermanent magnet. Current is passed through coil no. 1 in such a direction that a north poleis established and through coil no. 2 in such a direction that a south pole is established. Apermanent magnet with a north and South Pole is the moving part of this simple motor. InFigure 5-a, the north pole of the permanent magnet is opposite the North Pole of theelectromagnet. Similarly, the south poles are opposite each other. Like magnetic poles repeleach other, causing the movable permanent magnet to begin to turn. After it turns part wayaround, the force of attraction between the unlike poles becomes strong enough to keepthe permanent magnet rotating. The rotating magnet continues to turn until the unlikepoles are lined up. At this point the rotor would normally stop because of the attractionbetween 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 andrepel each other. (Figure-2.4 C). The movable permanent magnet would then continue torotate. If the current direction in the electromagnetic coils was changed every time themagnet 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 thesimple device shown above, but the principle is the same.



6.3 Producing Mechanical ForceAs in the generator, the motor has a definite relationship between the direction of themagnetic flux, the direction of motion of the conductor or force, and the direction of theapplied voltage or current.

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

6.4 General Construction of DC MachinesA 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

Figure-2.5 Four Pole DC Motor



6.5 Four Pole DC Motor

6.5.1 Armature Core or StackThe armature stack is made up thin magnetic steel laminations stamped from sheet steelwith a blanking die. Slots are punched in the lamination with a slot die. Sometimes thesetwo operations are done as one. The laminations are welded, riveted, bolted or bondedtogether.

6.5.2 Armature WindingThe armature winding is the winding, which fits in the armature slots and is eventuallyconnected to the commutator. It either generates or receives the voltage depending onwhether the unit is a generator or motor. The armature winding usually consists of copperwire, either round or rectangular and is insulated from the armature stack.

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

6.5.4 Field CoilsThe field coils are those windings, which are located on the poles and set up the magneticfields 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 serieswindings (in series with the armature winding) or a combination of both.

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

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

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



6.5.8 InterpolesInterpoles are similar to the main field poles and located on the yoke between the mainfield poles. They have windings in series with the armature winding. Interpoles have thefunction of reducing the armature reaction effect in thecommutating zone. They eliminate the need to shift thebrush assembly.

6.5.9 Frame, End Bells, Shaft, and BearingsThe frame and end bells are usually steel, aluminum ormagnesium castings used to enclose and support thebasic machine parts. The armature is mounted on a steelshaft, which is supported between two bearings. Thebearings are sleeve, ball or roller type. They are normallylubricated by grease or oil.

6.5.10 Back End, Front EndThe load end of the motor is the Back End. The oppositeload end, most often the commutator end, is the FrontEnd of the motor.

6.6 Shunt Wound - DC Operation TypicalSpeed - Torque CurveShunt wound motors, with the armature shunted acrossthe field, offer relatively flat speed-torquecharacteristics. Combined with inherently controlled no-load speed, this provides good speed regulation overwide load ranges. While the starting torque iscomparatively lower than the other DC winding types,shunt wound motors offer simplified control forreversing service.

6.7 Compound Wound - DC Operation Typical Speed - Torque CurveCompound wound (stabilized shunt) motors utilize a field winding in series with thearmature in addition to the shunt field to obtain a compromise in performance between aseries and shunt type motor. This type offers a combination of good starting torque andspeed stability. Standard compounding is about 12%. Heavier compounding of up to 40 to50% can be supplied for special high starting torque applications, such as hoists and cranes.

6.8 Series Wound - DC Operation Typical Speed - Torque Curve



Series wound motors have the armature connected in series with the field. While it offersvery high starting torque and good torque output per ampere, the series motor has poorspeed 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 loadbecause of their tendency to "run away" under no-load conditions. These are generally usedon crane and hoist applications.

6.9 Permanent Magnet - DC Operation Typical Speed - Torque CurvePermanent magnet motors have no wound field and aconventional wound armature with commutator andbrushes. This motor has excellent starting torques, withspeed regulation not as good as compound motors.However, the speed regulation can be improved withvarious designs, with corresponding lower rated torquesfor a given frame. Because of permanent field, motorlosses is less with better operating efficiencies. Thesemotors can be dynamically braked and reversed at somelow armature voltage (10%) but should not be plugreversed with full armature voltage. Reversing currentcan be no higher than the locked armature current.

6.10 Brush ShiftingOne method of reducing the arcing due to non-linear commutation is to shift the brushesaway from the geometrical neutral position. Then commutation will occur when theapplicable coil is under the influence of a weak magnetic field that will generate a voltage inthe coil, which opposes the induced voltage due to current change. Therefore, this newvoltage will assist rather than hinder the current reversal. In a generator, it is necessary toshift the brushes forward in the direction of rotation for good commutation. This is truebecause 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 thenext pole, it will be assisted by the current reversing voltage.In a motor, it is necessary to shift the brushes against thedirection of rotation because current flow is in opposition tothe induced voltage. The amount of shift necessary dependson the load so a given shift will not be satisfactory for allloads. One effect of shifting brushes is that ademagnetization component of armature reaction isintroduced. In other words, when the brushes are shifted,the armature reaction will not only distort the main fieldflux but it will also directly oppose the main field. This will



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

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

In a series motor the drop in speed with increased torque is much greater. This is due to thefact that the field flux increases with increased current, thus tending to prevent thereduction in back EMF that is being caused by the reduction in speed. The field flux varies ina series motor and the torque varies as the square of the armature current until saturationis reached. Upon reaching saturation, the curve tends to approach the straight line trend ofthe 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 seriesmotor.

6.12 Speed RegulationSpeed regulation is the change in speed with the change in load torque, other conditionsbeing constant. A motor has good regulation if the change between the no load speed andfull 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 itresults in the more deliberate movement of heavier loads. Also, the slowing down of theseries motor is better for heavy starting loads. However, for many applications the shuntmotor is preferred.

6.13 Motor StartingWhen the armature is not rotating, the back EMF is zero and the total applied voltage isavailable for sending current through the armature. Since the armature resistance is low, anenormous current would flow if voltage were applied under this condition. Therefore, it isnecessary to insert an additional resistance in series with the armature until a satisfactoryspeed is reached where the back EMF will take over to limit the current input.



6.14 Losses

6.14.1 Friction and WindageThese losses include bearing friction, brush friction, and windage. They are also known asmechanical 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 windageincrease as the cube of the speed.

6.14.2 Armature Copper LossesThese 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 thecurrents.

6.14.3 Field Copper LossesThese are the I2 R losses of the field circuit which can include the shunt field winding, seriesfield 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 LossesThese are the hysteresis and eddy current losses in the armature. With the continual changeof direction of flux in the armature iron, an expenditure of energy is required to carry theiron through a complete hysteresis loop. This is the hysteresis loss. Also since the iron is aconductor and revolving in a magnetic field, a voltage will be generated. This, in turn, willresult in small circulating currents known as eddy currents. If a solid core were used for thearmature, the eddy current losses would be high. They are reduced by using thinlaminations, which are insulated from each other. Hysteresis and eddy current losses varywith flux density and speed.

6.15 EfficiencyFor 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 motorthe opposite is true, therefore:

6.16 Horsepower BasicsIn 18th century England, coal was feeding the industrial revolution and Thomas Newcomeninvented a steam driven engine that was used to pump water from coal mines. It was a Scott



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

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

If steam engines had been developed someplace else in the world, where the horse was notthe 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, dogsleds, etc.

Horsepower and Electric Motors

Formulae to calculate power of electric motors in HP:



7 ConclusionOur internship project was that to design a speed control circuit for a DC Motor. The simulationsindicate that this circuit is very easy to implement, in this circuit. Fewer components are used due towhich troubleshooting is made easy. As MCU is used in this circuit so it is more precise, accurate andreliable.

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



8 Appendices

Appendix A

Programming Code of MCUinclude 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



movlw b'10000001' ;ADCS=10 CHS=AN0 ADON=ON

movwf adcon0 ;Set ADCON0 register


movlw b'00001110' ;ADFM=0 PCFG=1110

movwf adcon1 ;Set ADCON1 register


;*** PWM initialization

clrf tmr2 ;Clear TMR2 register

movlw b'11111111' ;Max duty (low speed)

movwf ccpr1l ;Set CCPR1L register


movlw d'255' ;Period=1638.4usec(610Hz)

movwf pr2 ;Set PR2 register


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



;*** Interruption control


movlw b'00000001' ;CCP2IE=Enable

movwf pie2 ;Set PIE2 register


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 ---



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



goto led2 ;No.






goto led3 ;No.








goto led4 ;No.






goto led5 ;No.






goto led6 ;No.






goto led7 ;No.






goto led8 ;No.



led8 movlw b'11111111' ;Set LED control data



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

int_end

movwf portb ;Set PROTB

retfie

;********************************************************

; END of DC motor speed controller

;********************************************************

End

Appendix B

PIC16F87XA Data Sheet28 Pin Enhanced Flash Microcontrollers

High-Performance RISC CPUOnly 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 to256 x 8 bytes of EEPROM Data Memory



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

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

Timer1: 16-bit timer/counter with prescaler, can be incremented during Sleep via externalcrystal/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 Features10-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 Features100,000 erase/write cycle Enhanced Flash program memory typical

1,000,000 erase/write cycle Data EEPROM memory typical

Data EEPROM Retention > 40 years



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 TechnologyLow-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

MOSFET FA57SA50LC Data Sheet



Appendix D

Bridge Rectifier 2W005G Datasheet



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 ResourcesBook: “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

Web: http://www.alldatasheets.com

http://www.wikipedia.org/

http://www.google.com/

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

http://www.alldatasheets.com/

speed control of dc motor

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