Post on 14-Apr-2018
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Unit III
SRM
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2
Introduction of SRM :
The reluctance motor is an electric motor in whichtorque is produced by the tendency of its moveable part to
move to a position where the inductance of the excited
winding is maximized.
Principle of SRM
SRM develops torque through an interact ion between
the electrom agnet exci tat ion from the stator poles and
the rotor teeth, once a particu lar combinat ion o f phasecomment is establ ished and maintained in the stator,
the rotor pole wi l l be alignm ent wi th the stator po le in
that part icu lar po si t ion.
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Basic structure of SRM
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Stator pole
Rotor
pole
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When one stator phase is energized, its stator
pole pair attracts the closest rotor pole pairinto alignment producing torque.
By the consecutive energization of successivephases, continuous rotation in either directionis possible.
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The direction of rotation of motor depends
upon the sequence of switching the stator
windings.
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Construction of SRM
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BLOCK DIAGRAM OF SRM
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OPERATION PRINCIPLE
OPERATION PRINCIPLE
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OPERATION PRINCIPLE
cont..
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OPERATION PRINCIPLE
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OPERATION PRINCIPLE
cont..
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TorqueandInductanceplot
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Aligned position
Unaligned Position
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When one stator phase is energized, the statorpole pair attracts the closest rotor pole pairinto the field.
Torque produced on the basis of varyingreluctance along the magnetic circuit.
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When one stator phase is energized, the statorpole pair attracts the closest rotor pole pairinto the field.
Torque produced on the basis of varyingreluctance along the magnetic circuit.
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T=1/2 { i2(dL/d)}
L- inductance
-rotor angular position
i- current
T- torque
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Torque ripple pulsations are most significantat the commutation instants when torque
production mechanism is being transferred
from one active phase to another.
%Ripple factor = Tmax-Tmin* 100
Tavg
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Geometry
Switching devices in the input side
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Conventional type24/18-pole
BS=6.9,br=7.4
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24/18 POLE ANIMATED SRM
BS=6.9,br=7.4
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ADVANTAGES
The rotor does not have any windings.
Its strong and rugged constructionIt provides high reliability, wide-speed range
at constant power.
DISADVANTAGESDoubly-salient structure causes vibration
and acoustic noise.
High torque-ripple
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Possible Research Potential in SRM
1. Reducing vibration and noise.
2. Diminishing the torque ripples and
Improvising the torque output.
3. Geometrical variations to reduce
weight.
4. DSP based power converter for SRM -reducing torque r ipples .
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POWER CONVERTER
CIRCUIT
Application
Converter design
Cost of drive
Basic requirement
Freewheel chopping period
Demagnetizing energy back to supply
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TYPE OF CONVERTERS
Classic converter.
n+1 power converter.
Phase winding converter.
Spilit power converter.
Dump c Converter.
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Classic converter.
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Performance of CC
ADVANDAGE :
1. Control of each phase is completely
independent of the other source
2. Switching losses less
3. The energy from the off going phase is
feed back to the source, which result in
useful utilization of the energy .
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Performance of CC
Disadvantage:
Higher no of switches required in each
phase which makes the converter
expensive and used for low voltage
regulation .
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n+1 POWER CONVERTER.
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Performance of CC
Advantage :
1. The converter used lower number of
switching devices, so less cost2. the converter is able to free wheel during
the chopping ,thus reducing the switchingfrequency and losses .
3. Voltage rating of all switching devices andthe diode are low .
High torque ripple during de.. And mag.
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Split power converter.
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Performance of SPLIT C
Lower no switching devices
Fast demagnetizing of phase during
commutation
It is not feasible for low voltage
application
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DUMP C CONVERTER.
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Current Control Schemes
Based on current control
1. Hysteresis type current regulator
2. PWM type current regulator
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HYSTERESIS TYPE CURRENT
REGULATOR
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PWM type current regulator
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Computer Based Control Of
SRM
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ADVANTAGES
The rotor does not have any windings.
Its strong and rugged constructionIt provides high reliability, wide-speed range
at constant power.
DISADVANTAGESDoubly-salient structure causes vibration
and acoustic noise.
High torque-ripple