“Speed Control of a Switched Reluctance Motor Using Microcontroller” Major Project report submitted in partial fulfillment of the requirements For the award of the degree of
BACHELOR BA CHELOR OF TECHNOLOGY TECHNOLOGY IN ELECTRICAL AND ELECTRONIC ELECTRONICS S ENGINEERING ENGINEERING By DEEPTHI.S
(08241A0207)
JHANSI RANI.CH (08241A0213) MOUNICA.P
(08241A0223)
Department De partment of Ele Electri ctri cal and Electronics Enginee ngineering ring
GOKARAJ GOKA RAJU U RANGARAJ RANGA RAJU U INSTITUT INSTITUTE E OF ENGINEER ENGINEERING ING & TECH TECHNOLOGY, NOLOGY, BACHUPALLY, HYDERABAD-72 2008 – 2012
GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING AND A ND TECHNOLOGY TECHNOL OGY Hyderabad, Hydera bad, An dhr a Pradesh.
DEPARTME
NT OF
E
CERTIFICATE This is to certify that the major-project report entitled SPEED CONTROL OF A SWITCHED RELUCTANCE MOTOR USING MICROCONTROLLER that is being submitted by MOUNICA.P, JHANSI RANI.CH, DEEPTHI.S in partial fulfillment for the award of the Degree of Bachelor of Technology in Electrical and Electronics Engineering to the Jawaharlal Nehru Technological University is a record of bonafide work carried out by them under my guidance and supervision. The results embodied in this project report have not been submitted to any other University or Institute for the award of any Graduation degree.
Mr.P.M. Mr.P. M.Sa Sarm rma a
Mr. C.K.sarma
HOD, EEE
Professor
GRIET
Dept. of EEE
Hyderabad
GRIET
Extern al Examiner
ACKNOWLEDGEMEN ACKNOWLEDGEMENT T
This is to place on record my appreciation and deep gratitude to the persons Without whose support this project would never seen the light of day. I wish to express my propound sense of gratitude to Mr. P. S. Raju, Director, G.R.I.E.T for his guidance, encouragement, and for all facilities to complete this project. I also express my sincere thanks to Mr.P.M.Sarma, Head of the Department, G.R.I.E.T and for extending their help. I have immense pleasure in expressing my thanks and deep sense of gratitude to my guide Mr. C.K.Sarma, Professor, Department of Electrical and Electronics Engineering, G.R.I.E.T for his guidance throughout this project. Finally I express my sincere gratitude to Mr. S. N.Saxena, Professor, Department of Electrical and Electronics Engineering, G.R.I.E.T and Mr.R.Anil Kumar, Assistant Professor, Department of Electrical and Electronics Engineering, G.R.I.E.T, and all the
members of faculty and my friends who contributed their valuable advice and helped to complete the project successfully.
DEEPTHI.S
(08241A0207)
JHANSIRANI.CH (08241A0213) MOUNICA.P
i
(08241A0223)
ABSTRACT Switched reluctance motor (like the stepper motor) carries windings only on the stator and operates on the reluctance principle .Its rotor position is sensed and used to switch on and switch off phase windings. It is now being made up to 0.5 to 80 KW and it is used in applications like washing machine, fans, aircrafts, vacuum cleaner, servo drives, Fuel pump operations etc Inductance of a phase winding in a switched reluctance motor varies with rotor position. Direction of the developed torque does not depend on the direction of current, but it does depend on change in inductance with respect to rotor position. For a unidirectional torque, current must be present in the coil only when the rate of change of coil inductance with rotor position is positive. Study of switching methods to obtain currents of the desired waveforms in an inductance are the main aim of the project.
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CONTENTS 1. Introduction 1.1 1.2 1.3
About Switched Reluctance Motor Advantages and Disadvantages of Switched Reluctance Motor Desired Waveform of Current In a Stator Coil
2. Switched Reluctance Motor Controllers 2.1 2.2 2.3 2.4 2.5
Construction Principle of Operation The Relationship Between Inductance and Rotor Position Aligned Inductance and Unaligned Inductance To Obtain the Current Waveform
3. Converters For Switched Reluctance Motor Drives 3.1 3.2 3.3
Power Converter Topology Energizing the Switched Reluctance Motor Torque Speed Characteristics of a Switched Reluctance Motor
4. Software Code 5. Hardware Description 5.1
Power Supply Section 5.1.1 Power supply circuit to the microcontroller 5.1.2 Power supply circuit for Switched Reluctance Motor
6. Schematic Connections in Proteus 6.1
Switching for MOSFET 6.1.1 Pulses for MOSFET Q1 6.1.2 Pulses for MOSFET Q2 6.2 Switching Circuit of Switched Reluctance Motor for Single Phase 6.2.1 Current waveform 6.3 Switching Circuit of Switched Reluctance Motor for Two Phases 6.3.1 Current waveform 6.4 Switching Circuit of Switched Reluctance Motor for Three Phases 6.4.1 Current waveforms 6.5 Simulation In MATLAB Software 6.5.1Specification of Switched Reluctance Motor 6.5.2Switched Reluctance Motor characteristics in MATLAB 6.6 EAGLE designs 6.6.1 Schematic layout of power supply circuit 6.6.2 Board layout of power supply circuit iii
6.6.3 Schematic layout of driver circuit 6.7 Difficulties Encountered During Simulation 6.7.1 Simulation in Proteus 6.7.2 Simulation in MATLAB
7. Hardware Implementation 7.1 7.2 7.3 7.4 7.5
Power Supply Circuit Driver Circuit Microcontroller Circuit Interfacing Microcontroller with Driver Circuit Complete Circuit Testing 7.5.1 current waveform 7.6 Difficulties Encountered on Hardware 7.6.1 First Difficulty 7.6.2 Second Difficulty
8. Conclusion and Scope for Future Work References Appendix A Appendix B Appendix C Appendix D Appendix E
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LIST OF FIGURES Figure 2.1 ------------------------------ 6/4 pole machines Figure 2.2 ------------------------------ Four distinct inductance regions emerge Figure 2.3 ------------------------------ Inductance profile Figure 2.4 ------------------------------ Aligned Position Figure 2.5 ------------------------------ Voltage PWM-Hard/Soft chopping Figure 2.6 ------------------------------ General Motor Control Design Figure 3.1------------------------------3.1---------------------------- --- Variation of reluctance of the flux path of a phase Figure 3.2 ------------------------------ Half-Bridge Inverter Figure 3.3 ------------------------------ Torque Speed Characteristics of a Switched Reluctance Motor Figure 5.1 ------------------------------ Power supply Circuit for microcontroller Figure 5.2 ------------------------------ Power Supply Circuit for Switched Reluctance Motor Figure 6.1 ------------------------------ Switching circuit of Switched Reluctance Motor for three phases Figure 6.2 ------------------------------ Current waveform across three phase windings Figure 6.3 ------------------------------ Circuit connections in MATLAB Figure 6.4 ------------------------------ Switched Reluctance Motor characteristics in MATLAB simulation
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CHAPTER 1 INTRODUCTION 1.1 ABOUT SWITCHED RELUCTANCE RELUCTANCE MOTOR Electrical machines can be classified into two c ategories on the basis of how torque is developed in them: electromagnetically or through variation of reluctance. In the first category, motion is produced by b y the interaction of two magnetic fields, one generated by the stator and the other by the rotor. Two magnetic fields, mutually coupled, produce an electromagnetic torque tending to bring the fields into alignment. The same phenomenon causes opposite poles of bar magnets to attract and like poles to repel. The vast majority of motors in commercial use today operate on this principle. In the second category, motion is produced as a result of the variable reluctance in the air gap between the rotor and the stator. When a stator winding is energized, producing a single magnetic field, reluctance torque is produced by the tendency of the rotor to move to its minimum reluctance position. This phenomenon is analogous to the th e force that attracts iron or steel or steel to permanent magnets. In those cases, reluctance is minimized when the magnet and metal come into physical contact. Switched reluctance motor falls into this class of machines. In Switched reluctance motor, switching of supply from one stator to the next causes minimum reluctance position of the rotor to change continuously thus producing rotation. By controlling the switching strategy, and the current flowing through the stator coils, we can control the torque and an d the speed of the motor. Because of their simple mechanical construction switched reluctance motors are of low cost. This has motivated a large amount of research on these motors in the last decade. The mechanical simplicity of the device, however, ho wever, comes with some limitations. Like the brushless the brushless dc motor, switched reluctance motors cannot run directly from a dc bus or an ac bus, but must always be electronically commutated. Also, the saliency of the stator and rotor, necessary for the machine to produce reluctance torque, causes strong non-linear magnetic characteristics, complicating the analysis and control of the Switched Reluctance Motor.
1.2 Advantages and Disadvantages of Switched Reluctance Motor: Advantages: The switched reluctance motor possess a few un ique features that makes it a vigorous competitor to existing AC and DC motors in various adjustable-speed drive and servo applications. 1. The torque–speed characteristics of the motor can be modified to the application requirement more easily during the design stage than in the case of induction and permanent magnetic machines. 2. The starting torque can be very high without the problem of excessive in-rush current due to its higher Self inductance. 3. There are independent stator phases, which do not prevent drive operation in the case of loss of one or more phases.
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Disadvantages: The Switched Reluctance Motor also comes with a few disadvantages among which torque ripple and acoustic noise are the most critical. The higher torque ripple also cau ses the ripple current in the DC supply to be quite large, necessitating a large filter capacitor.
1.3 Desired waveform of current in a stator coil The ideal waveform of current in a stator phase will be shown to be a square waveform. The attempt is to get the actual waveform wav eform as close to the ideal as a s possible.
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CHAPTER 2 SWITCHED RELUCTANCE MOTOR CONTROLLER 2.1 CONSTRUCTION Switched Reluctance Motor has wound field coils of a dc motor for its stator windings and has no coils or magnets on its rotor. Both the stator and rotor have salient poles, hence the machine is referred to as a doubly salient machine. Switched Reluctance Motors are made up of laminated stator and rotor cores with Ns=2mq poles on the Stator and Nr poles on the rotor. The number of phases is m and each phase is made up of concentrated coils place on 2q stator poles. Most favored configuration amongst many options a re 6/4 three phase and 8/6 four phase Switched Reluctance Motors’s as shown in the figure 2.1. These two configurations correspond to q = 1(one pair of stator poles and coils per phase) but q may be equal to 2 or 3 also.
Figure 2.1 6/4 pole machines 2.2 PRINCIPLE OF OPERATION With only one phase switched on; the rotor will be at rest in a position which provides minimum reluctance for the flux produced by that phase. In this position, there will not be any developed torque on the rotor. Now if that phase is switched off and another phase switched on; the rotor experiences a torque tending to move it to a minimum reluctance position corresponding to the new phase. Whichever direction of movement offers the least distance to be moved by the rotor to reach the new minimum reluctance position is the direction of rotor motion.
Expression for Developed Torque: Singly excited electromagnetic relays have been analyzed using the principles of electromechanical energy conversion Expressions for electromagnetic torque have been developed. These results can be extended to the switched reluctance motor, and the expression for the torque is obtained as
The following are the implications of equation (1): 1. The torque is proportional to the square of the current so, current can be in either direction, still unidirectional torque is produced. This is a distinct adva ntage in that only one power switch is required for control of current in a phase winding. This feature reduces the number o f power switches in the converter and thereby makes the drive economical
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2. The torque constant is given by the slope of the inductance vs. rotor position characteristic. It is understood that the inductance of a stator winding is a function of both the rotor position and current, thus making it nonlinear. Because of its nonlinear nature, a simple equivalent circuit development for this motor is not possible. 3. Since the torque is proportional to the square of the current hence, it has a good starting torque. 4. The direction of rotation can be reversed by changing the sequence of stator poles excitation, which is a simple operation.
2.3 THE RELATIONSHIP BETWEEN INDUCTANCE AND ROTOR POSITION Since the torque characteristics are dependent on the relationship between flux Linkages and rotor position as a function of current, it is worthwhile to conceptualize the control possibilities and limitations of this motor drive. For example, a typical phase inductance vs. rotor position is shown in Figure below 2.5 for a desired phase current. The significant inductance p rofile changes are determined in terms of the stator and rotor pole arcs and number of rotor poles. The rotor pole arc is assumed to be greater than the stator pole arc for this illustration, which is usually the case. From Figures 2.3(a) and 2.3 (b), the various angles are derived as:
Figure 2.2 Four distinct inductance regions emerge
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Where βs and βr are stator and rotor pole arcs, respectively, and
is the number of rotor poles.
Figure 2.3 Inductance profile
1. 0 − θ1 and θ4 − θ5: The stator and rotor poles are not aligned in this region and the flux is predominantly determined by the air path, thus making the inductance minimum and almost a constant. Hence, in this region there is no torque production. The inductance in this region is known as
2.
.
θ1 − θ2:
Poles are aligned, so the flux path is mainly through stator and rotor laminations. This increases the inductance with the rotor position, giving it a positive slope. A current impressed in the winding during this region produces a positive (i.e., motoring) torque. This region comes to an end when the aligning of poles is complete. 3. θ2 − θ3: During this period, movement of rotor pole do es not alter the complete align of the stator pole and does not change the dominant flux path. This has the effect of keeping the inductance maximum and constant, and this inductance is known as
.
4. θ3 − θ4: The rotor pole is moving away from aligned stator pole in this region. This is very much similar to the θ1 − θ2 region, but it has decreasing inductance and increasing rotor position contributing to a negative slope of the inductance region. The operation of the machine in this region results in negative torque (i.e., generation of electrical energy from mechanical input to the switched reluctance machine).It is not possible to achieve the ideal inductance profiles shown in Figure above in an actual motor due to saturation.
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2.4 ALIGNED AND UNALIGNED INDUCTANCE Let LA be the aligned inductance of a coil/Phase and LU be the unaligned inductance of the coil / phase. βs and βr are stator and rotor pole arcs, respectively. Let us assume that βr > βs and LA >LU.
Figure 2.4 Aligned Position CASE 1: When θ=0 Axis of the stator pole is in alignment with the rotor pole as shown in the figure 2.4(a). Therefore the inductance of the coil is LA, because the stator reference axis and rotor reference axis are in alignment. At this position flux linkage of phase winding of stator has maximum value and hence inductance of phase winding has maximum value for given current.
Figure 2.4(a)
of rotor pole is along the edge of stator pole. At this position reluctance is minimum. Then the
Figure 2.4(b)
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In this position, the flux pattern is such that the flux linkages / unit current of the stator is less than the previous case but not minimum. Therefore L < LA and L > LU.
Figure 2.4(c)
Figure 2.4(d)
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Figure 2.4(e)
2.5 TO OBTAIN THE CURRENT WAVEFORM
Figure 2.5 Voltage PWM-Hard/Soft chopping Voltage PWM chopping can be realized in two ways with this drive topology, soft chopping and hard chopping. Figure 2.5 shows the difference and the phase current, flux linkage, voltage and inductance profile. Soft chopping is when only the high side power switch is chopping; the other switch remains permanently on. Hard chopping is when both transistors are switched on/off together. It generally produces more electric noise, it also generates more current ripples, and therefore soft chopping was realized in this application.
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The Figure2.6 shows a schematic for general motor control design with a microcontroller.
Figure 2.6 General Motor Control Design The function of the components in detail: Main supply: Provides circuits energy. Microcontroller power supply : Regulates voltage and current for the microcontroller Microcontroller: Produces the accurate signals for switching the MOSFETS also contains protection circuit, which ensures that a certain current value is not exceeded. Driver: Switches the power necessary for the motor phases
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CHAPTER 3 CONVERTERS FOR SWITCHED RELUCTANCE MOTOR DRIVES 3.1 POWER CONVERTER TOPOLOGY: As indicated by its name, phase-to-phase switching in the Switched Reluctance Motor drive must be precisely timed with rotor position to obtain smooth rotation and the optimal torque output. Rotor position feedback, or "sensor less" feedback method, is needed for proper control. It is well known that this phase-to-phase switching is realized by power semiconductors. The power converter topology has great influence on the Switched Reluctance Motor’s performance.
Switching Strategy: Switched Reluctance Motor’s are controlled by synchronizing the energizations of the motor phases with the rotor position.
Figure 3.1 Variation of reluctance of the flux path of a phase The shape of this curve is decided by number of teeth on stator and rotor, which will be different. As long as dR/dθ is negative; torque will aid the motion and we would like to keep the current going. When dR/dθ becomes positive; torque opposes motion and we switch off current in that phase. To achieve an approximation to this current, we have to use PWM for supply voltage .Control of speed is achieved by varying the magnitude of the phase voltage. (Larger voltage larger current larger torque larger steady state speeds)
3.2 ENERGIZING THE SWITCHED RELUCTANCE MOTOR The Switched Reluctance Motor is energized using an Asymmetric Half Bridge Inverter shown in figure 3.2. This is a common topology used for this type of motor as it allows each phase to be energized independently. There are three voltages that can be applied to the stator windings. Consider phase-A, the voltage applied to the phase winding is +Vs when the Q1 and Q2 are on (+Vs-Q1-phase a-Q2- -Vs). Phase current then increases through both switches. If Q1 is off while the Q2 is still on, the winding voltage will be zero. Phase current then slowly decreases by freewheeling through Q1and D1.When Q1 and Q2 are off, the phase winding will experience –Vs voltage. Phase current then quickly decreases
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through both diodes (-Vs-D2-phase a-D1-+Vs). By appropriately coordinating the above three switching states, phase current of the Switched Reluctance Motor controlled.
Figure 3.2 Half-Bridge Inverter
3.3 TORQUE SPEED CHARACTERISTICS OF A SWITCHED RELUCTANCE MOTOR 1) In a Switched Reluctance Motor, a dc voltage is used to switch on the phases in succession. 2) During the period a phase is ON. a) Current in it is assumed constant b) Its inductance is assumed to increase linearly 3) V vs. I equation while a phase is ON
R‐resistance of coil
Where
=flux linkages of coil due to current
φ is a function of rotor position θ and i(t), both of which are function of t.
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φ =
( θ,i)
Transformer rotational Emf
Emf
If we assume i(t) is a constant;
V=R i(t)
5) Low Speed Operation: Because of low speed, neglect induced emf.
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With I constant at Irated; Td=constant= KIrated . If we keep increase V such that ‘i’ is I rated; power input increases, while developed torque is constant at Td. But for power balance,
This continues till a speed called base speed is reached .Beyond that speed, supply voltage cannot be increased any more, EMF increases. So current will decreases, torque will decreases.
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Figure 3.3 Torque Speed Curve for a Switched Reluctance Motors
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CHAPTER 4 SOFTWARE CODE //Program for switching the MOSFETS using AT89S52 #include sbit pulse=P1^0; sbit pulse1=P1^7; sbit pulse2=P2^0; sbit pulse3=P2^7; sbit pulse4=P3^0; sbit pulse5=P3^7; void delay(); void delay1(); void main() { int i; while(1) { for(i=1;i<=3;i++) { pulse=1; pulse1=1; pulse2=0; pulse3=0; pulse4=1; pulse5=1; delay1(); pulse1=0;
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pulse5=0; delay1(); } for(i=1;i<=2;i++) { pulse=1; pulse1=1; pulse2=0; pulse3=0; pulse4=0; pulse5=0; delay1(); pulse1=0; delay1(); } for(i=1;i<=3;i++) { pulse=1; pulse1=1; pulse2=1; pulse3=1; pulse4=0; pulse5=0; delay1(); pulse1=0; pulse3=0; delay1(); }
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for(i=1;i<=3;i++) { pulse=0; pulse1=0; pulse2=1; pulse3=1; pulse4=0; pulse5=0; delay1(); pulse3=0; delay1(); } for(i=1;i<=2;i++) { pulse=0; pulse1=0; pulse2=1; pulse3=1; pulse4=1; pulse5=1; delay1(); pulse3=0; pulse5=0; delay1(); } for(i=1;i<=3;i++) {
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pulse=0; pulse1=0; pulse2=0; pulse3=0; pulse4=1; pulse5=1; delay1(); pulse5=0; delay1(); } } } void delay1() { TMOD=0X01; TL0=0XC0; TH0=0XFD; TR0=1; while(TF0==0); TF0=0; TR0=0; }
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CHAPTER 5 HARDWARE DESCRIPTION 5.1 POWER SUPPLY SECTION 5.1.1 Power Supply to the Microcontroller
Figure 5.1 Power supply Circuit for microcontroller
Power supply block consists of following units: 1) Step down transformer. 2) Full wave rectifier circuit. 3) Input filter. 4) Voltage regulators. 5) Output filter. 6) Indicator unit.
Step down transformer: The step-down transformer is used to step down the supply voltage of 230v ac from mains to lower values, as the various devices used in this project require reduced voltages. The outputs from the secondary coil which is center tapped are the ac values of 0v, 15v and-15v.The conversion of these ac values to dc values is done using the full wave rectifier unit.
Rectifier Unit: The rectifier circuit is used to convert the ac voltage into its corresponding dc voltage. The most important and simple device used in rectifier circuit is the diode. The simple function of the diode is to conduct when forward biased and not to conduct in reverse bias.
Regulator unit: Regulator regulates the output voltage to a specific value. The output voltage is maintained irrespective of the fluctuations in the input dc voltage. Whenever there are any ac voltage fluctuations, the dc voltage also changes.
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Regulators used in this application are: 1.7805 which provides 5v dc 2.7812 which provide 12v dc
Output Filter: This filter is fixed after the Regulator circuit to filter any of the possibly found ripples in the output received finally. Capacitors used here are of value 10UF.
5.1.2 Power Supply Circuit for Switched Reluctance Motor As indicated by its name, phase to phase switching in the Switched Reluctance Motor drive must be precisely timed with rotor position to obtain smooth rotation and the optimal torque output. Rotor position feedback or “sensor less” feedback method, is needed for proper control topology has great The most common approach to the powering of a switched reluctance motor is to u se an asymmetric bridge.
Figure 5.2
Power Supply Circuit for Switched Reluctance Motor
Operation: This is a common topology used for this type of motor as it allows each phase to be energized independently. Consider phase-A, the voltage applied to the phase winding is +12V when the Q1 and Q2 are on (+Vs-Q1-phase a-Q2- -Vs). Phase current then increases through both switches. If Q1 is off while the Q2 is still on, the winding voltage will be zero. Phase current then slowly decreases by freewheeling through Q1and D1.When Q1 and Q2 are off, the phase winding will experience -12V voltage. Phase current then quickly decreases through both diodes (-Vs-D2-phase a-D1-+Vs). By appropriately coordinating the above three switching states, phase current of the Switched Reluctance Motor controlled.
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CH SCHEMATI 6.1 SWI CHIN
FOR
PTER 6 CON
ECTI
NS
OSFET
We conside a circuit h ving a 10o m resistanc , 20mH of nductance s shown below.
We divide one cycle into fourteen parts.
t t=0, s itch is at position
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Time Periods
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
T13
T14
T15
(m sec)
2.23
6.93
3.56
4.05
5.1
2.87
6.93
2.23
9.1
1.82
12…03
1.54
16.09
5.52
80
6.1.1Pulses for MOSFET Q1
6.1.2Pulses for MOSFET Q2
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6.2 SWITCHING CIRCUIT OF SWITCHED RELUCTANCE MOTOR FOR SINGLE PHASE
6.2.1 Current Waveform
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6.3 SWITCHING CIRCUIT OF SWITCHED RELUCTANCE MOTOR FOR TWO PHASE
6.3.1 Current Waveforms
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6.4 SWITCHING CIRCUIT OF SWITCHED RELUCTANCE MOTOR FOR THREE PHASE
Figure 6.1 Switching circuit of Switched Reluctance Motor for three phases
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6.4.1 Current Waveforms
Figure 6.2 Current waveform across three phase winding
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6.5 SIMULATIONS IN MATLAB SOFTWARE 6.5.1 Specifications of Switched Reluctance Motor: Stator resistance
: 0.01 Ohm/phase
Inertia
: 0.0082 Kg.m2
Friction
: 0.01N m s
Initial speed
: 0 rad/sec
Position
: 0 rad
Unaligned Inductance
: 0.7mH
Aligned Inductance
: 20mH
Maximum Current
: 450A
Maximum Flux Linkage
: 0.486 Weber-turn
Figure 6.3 Circuit connections in MATLAB
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6.5.2 Switched Reluctance Motor Characteristics in MATLAB
Figure 6.4 Switched Reluctance Motor characteristics in MATLAB simulation
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6.6 EAGLE DESIGNS 6.6.1 Schematic Layout of Power Supply Circuit
6.6.2 Board Layout of Power Supply Circuit
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6.6.3 Schematic Layout of Driver Circuit
6.7 DIFFICULTIES ENCOUNTERED DURING SIMULATION 6.7.1 Simulation in Proteus
Here the inductance value is 5mH and this is the current waveform which is not accurate. Hence we have find out the inductance range i.e.; 15mH to 30mH with resistance of below 20 Ώ
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6.7.2 Simulation in MATLAB
Current and Speed Waveforms
This is for the frequency of 200Hz, the speed oscillates continuously and after certain time p eriod it oscillates in the negative direction. For which the motor stops running.
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CHAPTER 7 HARDWARE IMPLEMENTATION 7.1 POWER SUPPLY CIRCUIT
The power supply circuit consists of two IRFZ540N mosfets, two d iodes, one inductor of 20mH with 1ohm internal resistance is considered as one phase winding of the motor.The MOSFET Q2 is on and off for eight times,where as MOSFET Q1 is continou sly on.After that the two MOSFETS should be turned off for some period.And then the cycle repeats. when the MOSFET Q1 and Q2 are on (+Vs-Q2 phase winding-Q1- -Vs). Phase current then increases through both switches. If MOSFET Q2 is off while the Q1 is still on, the voltage through phase winding will be zero. Phase current then slowly decreases by freewheeling through Q2and D2.When Q1 and Q2 are off, the phase winding will experience -12V voltage. The current through phase winding quickly decreases through both diodes (Vs-D1-phase a-D2-+Vs). By appropriately coordinating the above three switching states, phase current of the SWITCHED RELUCTANCE MOTOR can be controlled.
7.2 DRIVER CIRCUIT The Driver circuit is used to turn on MOSFETS, the gate terminal must be set to a voltage at least 15 volts greater than the source terminal.One feature of power MOSFETs is that they have a large stray capacitance between the gate and the other terminals. The effect of this is that when the pulse to the gate terminal arrives, it must first charge this capacitance up before the gate voltage can reach the 15 volts required. The gate terminal then effectively does take current. Therefore the circuit that drives the gate terminal should be capable of supplying a reasonable current so the stray capacitance can be charged up as quickly as possible. The best way to do this is to use a dedicated MOSFET driver chip.
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This is the driver circuit we are using for switching the MOSFETS.74LS 40 IC an TLP250 IC are used in this circuit.The pins used in microcontroller are connecte to input pin of 74LS 40 IC, then this is connected to output pin.At this pin voltage is step up.That output Voltage is given to the gate terminals of the MOSFET. In this way the MOSFETS are on.
7.3 MICROCONTROLLER CIRCUIT
The microcontroller is embedded with a C program. It is designed in such a way that the ports should be on/off at appropriate times. These pulses are giving to MOSFETS. The output is checking with an oscilloscope.
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8051 chips are used in a wide variety of control systems, telecom applications, and robotics as well as in the automotive industry. By some estimation, 8051 family chips make up over 50% of the embedded chip market. The 8051 architecture developed by Intel has proved to be the most popular and enduring type of microcontroller, available from many manufacturers and widely used for industrial applications and embedded systems as well as being a versatile and economical.
7.4 INTERFACING MICROCONTROLLER WITH DRIVER CIRCUIT
The pins used in microcontroller are giving to the inputs of driver circuit,then the output pins of the driver circuit is giving to the gate terminal of the MOSFETS.
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7.5 COMPLETE CIRCUIT TESTING
Checking the current waveform across the phase winding (inductor of 20mH).Here we are connecting a 10ohm resistor in series with an inductor, the probes of oscilloscope are put across the resistor. The output is seen in the oscilloscope. The current waveform is as shown below.
7.5.1 Current waveform
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7.6 DIFFICULTIES ENCOUNTERED ON HARDWARE: 7.6.1 First Difficulty
We have considered secondary winding of the transformer, rating of 15v-0v-15v, 500MA L=62. 5mH with internal resistance of R=65 Ω. The resistance value is very high, due to this reason the required waveform is not obtained.
The current waveform looks like this
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7.6.2 Second Difficulty
We have considered an rectangle core material, and we have turned 200 turns, the inductance of the core coil 1mH and resistance is 140 ohms, which is not sufficient to get the required waveform.
The current waveform looks like this
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CHAPTER 8 CONCLUSION AND SCOPE OF FUTURE By the end of this project ---> Switched Reluctance Motor Characteristics are studied. --->Connections and testing in Proteus is studied. --->Coding and compiling of a C program in Keil u Vision software is studied. --->Hardware implementation by connecting Schematic and making Board layout EAGLE is done successfully. ---->Connections in MATLAB software are studied. Switched Reluctance Motor characteristics are verified. --->The hardware kit is tested successfully by embedding the C program – Hex file in the AT89C51 Microcontroller. --->The operation of microcontroller is analyzed in simulation and practically.
Scope of the Project: We have considered an inductor as one phase winding of the motor. In future, when motor is available the same pulses are given to the MOSFETS through a driver circuit and the output current waveform is observed. Even the speed control of Switched Reluctance Motor is to be verified.
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REFERENCES [1] Website: www.wikipedia.com/8051 [2] Website: www.google.com/eagle_software [3] Website: http://www.ti.com/lit/an/spra420a/spra420a.pdf [4] Michael T.DiRenzo, “Switched Reluctance Motor Control”, [5] Website: www.isis.com/proteus [6] A K Ray, “Microprocessor and Microcontroller”,
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APPENDIX A SOFTWARE USED – PROTEUS It is used for the real time simulation of the Circuits involving co mplex ICs, Microcontrollers, Electromechanical devices etc.
System components ISIS Schematic Capture - a tool for entering designs. PROSPICE Mixed mode SPICE simulation - industry standard SPICE3F5 simulator combined with a digital simulator. ARES PCB Layout - PCB design system with automatic component placer, rip-up and retry auto-router and interactive design rule checking.
VSM - Virtual System Modeling lets co simulate embedded software for p opular microcontrollers alongside hardware design.
System Benefits Integrated package with common user interface and fully context sensitive help.
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APPENDIX B SOFTWARE USED – KEIL uVISION Keil was founded in 1986 to market add-on products for the development tools provided by many of the silicon vendors. Keil implemented the first C compiler designed from the ground-up specifically for the 8051 microcontroller. Keil provides a broad range of development tools like ANSI C compiler, assemblers, debuggers and simulators, linkers, IDE, library managers, real-time operating systems and evaluation for 8051, 251, ARM, and XC16x/C16x/ST10 families.
COMPILING A ‘C’ PROGRAM IN KEIL
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APPENDIX C SOFTWARE USED – EAGLE EAGLE is an EDA program by Cad Soft for creating printed circuit boards. The name is an acronym formed from Easy Applicable Graphical Layout Editor. Cad Soft Eagle and the company in September 2009, Premier Farnell sells a supplier of electronic components. The software consists of several components: Layout Editor, Sch ematic Editor, Auto router and an extensible component database. It is for the platforms Microsoft Windows, Linux and Mac OS X available. It exists for non-commercial use; a free version on a schematic sheet, half Euro card mm × 80 mm and two signal layers is limited to 100. The schematic editor can be used by a special component library for programming a MicroSPS is used.
Schematic and Board Layout in EAGLE
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APPENDIX D SOFTWARE USED – MATLAB A high-performance language for technical computing (Math works, 1998). MATLAB works with matrices. Everything MATLAB understands is a matrix (from text to large c ell arrays and structure arrays) .Various data types exist within MATLAB. Performance of MATLAB scripts can be improved using vector operations (more on this later).MATLAB has advanced data structures including object oriented programming functionality and over loadable operators.
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APPENDIX E DATA SHEETS
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