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Dr.(Mrs.)C.S.Rajeshwari
,
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Objectives
Introduction
Constructionand
operating
principle
Controlstrategy
Mathematicalmodel
Bldc motorapplications
Manufacturersofbldc motorintheWorld
Conclusion
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Introduction
Developmentinpowerelectronicshas
calledBLDC
motor.
Thesedrivearecosteffective,energyefficientandreliable.
BLDC
motor
has
become
alternative
to
.
Brushless
Direct
Current
(BLDC)
motors
areoneofthemotortypesrapidlygainingo ularit .
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Advantages &DisadvantagesofBrushlessDCMotors
Due to replacement of mechanical commutator by Electronic Commutator
Absence of sparking,
Has longer operating life and
ess ma n enance
Highly reliable
100,000 rpm.
Since armature winding is on stator, cooling is better. Hence higher specific
ou pu s can e o a ne
High efficiecy(75%), much quiter(due to absence of brushes) less length of motor
etc
Reduced radio interference causes small filter design
Pollution free since produce no brush /commutator particles/Gases as
ypro uc s o opera on
Can operate under submerged condition in fluids/combustible gases as they may
be hermatically sealed
Disadvantages:High Cost and low Starting Torque
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A BLDC motor is a Synchronous motor with a
permanent magnet rotor using semiconductor
currents such that the a constant maximum
speed.
Unlike conventional DC motor the function of
electronic commutator in BLDC motor.
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Therotorfluxdensitydistributionproducedby
thepermanentmagnetsisrepresentedbythe
greenspace
vector
Br.
Apowerprocessingunitsuppliesthreephase
currentstothestatorwindingsinsucha
mannerthat
the
resultant
stator
current
space
vectorIsis 90o aheadoftherotorfluxvector.
Themmf distributionproducedbythestator
currentsflowing
in
the
stationary
three
phase
windingsisequivalenttothatproducedbyIs
flowinginasinglesinusoidallydistributed
rotatingwinding
whose
magnetic
axis
lines
up
withIsasillustratedinthisanimation.
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CONSTRUCTIONAND
OPERATINGPRINCIPLE
A brushless dc motor has a rotor with permanent
magnets and a stator with windings. The control
energize the proper winding.
The magnetic field generated by the stator and
the rotor are rotates at the same frequency.
The function of the magnet is the same in both
motor.
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Ina
BLDC
motor,
t e
position
o
t e
rotor
is
sensedandcontinuall fedbacktothe
commutation
electronics
to
provide
for
appropriateswitching.
coupledwiththegivenrotorposition.
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Disassembledviewofabrushlessdc
motor
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BrushlessDCmotoralongwithelectroniccontroller
connected to a current regulated Voltage
source inverter comprising of 6 SCRs.
protect these from reactance voltage.
Rotor carries a commutating disc with0
Light sensitive or hall effect sensors are
fixed 120 0apaprt receiving light from fixed
.
receiving light and logic 0 when dark
The 3 fixed sensors and rotating
commu a ng sc ro a ng a ong w ro or
produce the required sensor code from
which electronic circuitary generates gating
be in synchronism with the rotors
mechanical position.
e s a or an ro or ge s oc e w eac
other and remain in synchronism at anyspeed
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BrushLessDC(3Phase2poleTrapezoidalPMAC)MotorDrives
windingsdisplacedby1200 andeachwindingspansoneachsideby600
WhenrevolvinginCCWdirection
upto 1200,
rotationfrom
the
position
,linkswithsouthpoleandallbottomconductorsofphaseAwilllinkwith
theNorth
pole.
SoVoltageinducedinPhaseAis,
Beyond1200 someconductorsattop
link with N ole and others S ole.
Sameiswithbottomconductors.
Voltageinduced inphaseAlinearlyreversesinnext60 rotation
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TorqueinBLDCmotorSince air gap flux is constant , the voltageinduced is proportional to speed of rotor.
During each 60 interval current enters onephase and comes out of another
phase.Therefore power supplied to themotor in each such interval
E = Ke m=
d
d= 2 E Id
e m d
Torque = T = P/ m
e d
= 2 KTIdorque s proport ona to
Id
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RegenerativeBrakinginBLDC
When speed reverses, polarityo in uce vo tage reverse.
Reversin hase currents reversethe source current Id
inverter and from inverter to dcsource,
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fed with current pulses.
each 1200 duration and
where induced voltageis constant andmaximum
Polarit of currentpulses is same as that ofinduced voltage
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T1T6,T1T2,T3T2,T3T4,T5T4,T5T6
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Duringoto60,iA=IdandiB=Id
CurrentiA enters
through
phase
A
and
leavesthroughphaseB
WhenT1T6areon,terminalsAandBareconnectedto+ve andve erminals ofthedc source Vd.
CurrentflowsfromVd,T1Ph.A,Ph.B and, A
positive
WhenT1andT6areturnedoffcurrentflowsfromPh.A ,Ph.B,diodeD3,vd and
diodeD4
SincethecurrentshastoflowagainstvoltageVd,rateofchangeofcurrent iwillbenegative
T1T6,T1T2,T3T2,T3T4,T5T4,T5T6
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LowCostBLDCMotor
Low cost BLDC motopr
em lo s onl 3 transistors
and 3 diode converter to
su l onl ositivecurrents or voltages to 3
motor hases
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Hall Effect devices which generally provide optimum size
and the best environmental capabilities versus cost.
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Backemf detectiontechniqueisusedfor
sensorless
operation
of
BLDC
motor.
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BLDCMOTORAPPLICATIONS Used
in
turn
table
drives
in
record
players,Tape drive
for
vrdio recorders,
spindledrivesinharddiskdrivs forcomputers
Lowcostlowpowerdrivesincomputerperipherals,Instrumentsandcontrol
systems
Usedinbiomedicallikecryogeniccoolersandartificialheartpumps
Usedfordrivingcoolingfansforelectroniccircuitsandheatsinks
Railways
Fan
110
V
DC. SolarbasedIrrigation/Pumpingmotor.
a e e o ar rac ng ower upp y.
EngineCoolingapplicationinAutomobiles.
AutomotiveReturnlessFuelpump.
ExternalRotorfanapplicationswherelowacousticnoiseisimportant
ElectricWheelchairwithDSPbasedcontroller.
ControlofRobotarmandTrackingapplication.
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Inconclusion,BLDCmotorshaveadvantagesoverbrushedDCmotorsand
inductionmotors.
Theyhavebetterspeedversustorquecharacteristics,highdynamicresponse,
hi hefficienc lon o eratin life noiselesso eration hi hers eedran es
ruggedconstruction
and
so
on.
, ,
wherespaceandweightarecriticalfactors.
Withtheseadvantages,BLDCmotorsfindwidespreadapplicationsin
automotive,appliance,aerospace,consumer,medical,instrumentationand
automationindustries.
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ThankYou
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