SWITCHED SWITCHED RELUCTANCE RELUCTANCE

MOTORSMOTORSBy : K.Chakrapani

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HISTORYHISTORY INVENTED BY DAVIDSON OF INVENTED BY DAVIDSON OF

SCOTLAND IN 1838 SCOTLAND IN 1838 WAL`KER INVENTED VARIABLE WAL`KER INVENTED VARIABLE

RELUCTANCE MOTOR IN 1920RELUCTANCE MOTOR IN 1920 BEDFORD AND HOFT FILED US BEDFORD AND HOFT FILED US

PATENTS ON SRM IN 1971PATENTS ON SRM IN 1971 HEWLETT PACKARD- USED SRM IN HEWLETT PACKARD- USED SRM IN

VOLUME APPLICATION VOLUME APPLICATION (DRAFTMASTER PLOTTER)(DRAFTMASTER PLOTTER)

INTRODUCTIONINTRODUCTION Principle of stepper motor; magnetic material Principle of stepper motor; magnetic material

suspended in magnetic field align in direction of suspended in magnetic field align in direction of field due to torquefield due to torque

Basically stepper motor; i.e. rotate through fixed Basically stepper motor; i.e. rotate through fixed angle [step angle] when input pulse is appliedangle [step angle] when input pulse is applied

Speed proportional to pulse frequency; Speed proportional to pulse frequency; pulse<200Hz-discrete rotation and pulse>16KHz-pulse<200Hz-discrete rotation and pulse>16KHz-continous rotationcontinous rotation

When step angle decreases, number of steps / When step angle decreases, number of steps / rev increasesrev increases

Stepper motors:#sr motors #pm motors Stepper motors:#sr motors #pm motors #hybrid motors#hybrid motors

PRIMARY CHOICE FOR SERVO APPLICATIONSPRIMARY CHOICE FOR SERVO APPLICATIONS LIKE AC MACHINES,SRM DO NOT REQUIRE LIKE AC MACHINES,SRM DO NOT REQUIRE

COMMUTATOR AND BRUSHESCOMMUTATOR AND BRUSHES HIGH PEAK TORQUE,POWER DENSITY,TORQUE HIGH PEAK TORQUE,POWER DENSITY,TORQUE

INERTIA RATIOINERTIA RATIO VARIABLE SPEED MACHINEVARIABLE SPEED MACHINE

RELUCTANCE MOTOR IS SALIENT POLE RELUCTANCE MOTOR IS SALIENT POLE SYNCHRONOUS MOTOR WITH NO FIELD WINDINGSSYNCHRONOUS MOTOR WITH NO FIELD WINDINGS

WHEN ARMATURE COILS ARE EXCITED, ROTOR WHEN ARMATURE COILS ARE EXCITED, ROTOR ALIGNS IN THE DIRECTION OF MINIMUM ALIGNS IN THE DIRECTION OF MINIMUM RELUCTANCE[RELUCTANCE TORQUE]RELUCTANCE[RELUCTANCE TORQUE]

T=3VT=3V22[Xd-Xq]Sin2{LOAD ANGLE}[Xd-Xq]Sin2{LOAD ANGLE}

2wXdXq2wXdXq V:PER PHASE RMS VOLTAGEV:PER PHASE RMS VOLTAGE W=SYNC SPEED RAD/SECW=SYNC SPEED RAD/SEC Xd:DIRECT AXIS RELUCTANCEXd:DIRECT AXIS RELUCTANCE Xq:QUAD AXIS RELUCTANCEXq:QUAD AXIS RELUCTANCE

CONSTRUCTION STATOR AND ROTOR ARE SALIENT IN STRUCTURE

STATOR WINDINGS ARE INDEPENDENT CONCENTRATED WINDINGS WHICH ARE EXCITED WITH SWITCHES FROM SOURCE

NO FIELD WINDINGS HENCE SINGLY EXCITED

FOR BIDERCTIONAL CONTROL AND SELF STARTING,NUM OF ROTOR POLES ARE LESS THAN NUM OF STATOR POLES

SINGLE STACK AND MULTI STACK CONSTRUCTION POSSIBLE

WORKING FIG SHOWS AN 8/6 SINGLE STACK WHICH HAS 4 PHASES A,B,C,D WHEN PHASE A IS EXCITED RELUCTANCE TORQUE CAUSES ROTOR

TO TURN UNTIL IT ALIGNS WITH AXIS OF PHASE A. EXCITATION IS CHANGED TO B AND A IS DEEXCITED BEFORE

ALIGNMENT ROTATION IS IN DIRECTION OF ENERGISATION DIRECTION OF ROTATION REVERSED BY REVERSING SEQUENCE

OF EXCITATION SPEED DEPENDS ON MAGNITUDE OF INPUT MICROSTEPPING CAN BE DONE FOR SINGLE STACK ONLY 1 ROTOR AND STATOR

TORQUE CHARACTERISTICSTORQUE CHARACTERISTICS DUE TO SALIENCY OF STATOR AND DUE TO SALIENCY OF STATOR AND

ROTOR,INDUCTANCE IS A FUNCTION OF ROTOR ROTOR,INDUCTANCE IS A FUNCTION OF ROTOR POSITIONPOSITION

A 6 ROTOR MACHINE HAS 6 MAX AND MIN VALUES OF A 6 ROTOR MACHINE HAS 6 MAX AND MIN VALUES OF INDUCTANCEINDUCTANCE

IF APPLIED INPUT IS V,IF APPLIED INPUT IS V, V{inst}=Ri+Ldi/dt +WmidL/d0V{inst}=Ri+Ldi/dt +WmidL/d0 BACK EMF,e=WBACK EMF,e=WmmidL/doidL/do i V{inst}=Rii V{inst}=Ri22+d(Li+d(Li22/2)/dt +Wmi/2)/dt +Wmi22dL/d0dL/d0 T=iT=i22/2dL/dO /2dL/dO INPUT=WINDING HEAT LOSS+RATE OF CHANGE OF INPUT=WINDING HEAT LOSS+RATE OF CHANGE OF

STORED MAGNETIC ENERGY+MECH POWER OUTPUT STORED MAGNETIC ENERGY+MECH POWER OUTPUT

MODES OF OPERATIONMODES OF OPERATION CONSTANT TORQUE MODE[CURRENT CONTROLCONSTANT TORQUE MODE[CURRENT CONTROL

CONSTANT POWER MODE[ANGLE CONTROL]CONSTANT POWER MODE[ANGLE CONTROL]

CONSTANT POWER*SPEED CONSTANT POWER*SPEED MODE[FORCEDCURRENT CONTROL WITH MODE[FORCEDCURRENT CONTROL WITH EXTERNAL RESISTANCE]EXTERNAL RESISTANCE]

WITH SOURCE VOLTAGE CONSTANT,Eb WITH SOURCE VOLTAGE CONSTANT,Eb INCREASES WITH SPEED ENOUGH TIME IS NOT INCREASES WITH SPEED ENOUGH TIME IS NOT AVAILABLE FOR CURRENT TO DEVELOPAVAILABLE FOR CURRENT TO DEVELOP

IN MODE II :WINDING IS CONNECTED TO SOURCE EARLIER IN MODE II :WINDING IS CONNECTED TO SOURCE EARLIER THAN ANGLE AT WHICH INDUCTANCE BEGINS TO RISETHAN ANGLE AT WHICH INDUCTANCE BEGINS TO RISE

CURRENT REACHES MAX VALUE;Eb INCREASES HENCE CURRENT REACHES MAX VALUE;Eb INCREASES HENCE CURRENT BEGINS TO FALLCURRENT BEGINS TO FALL

DUE TO CONSTANT DC SOURCE, FLUX INCREASES DUE TO CONSTANT DC SOURCE, FLUX INCREASES UNIFORMLY UNTIL CURRENT IS REVERSED AFTER WHICH UNIFORMLY UNTIL CURRENT IS REVERSED AFTER WHICH FLUX DECREASES UNIFORMLYFLUX DECREASES UNIFORMLY

HENCE CURRENT AND FLUX BECOMES ZERO WHEN HENCE CURRENT AND FLUX BECOMES ZERO WHEN NEGATIVE CYCLE OF VOLTAGE IS COMPLETEDNEGATIVE CYCLE OF VOLTAGE IS COMPLETED

OPERATES IN THIS MODE UPTO UPPER THRESHOLD OPERATES IN THIS MODE UPTO UPPER THRESHOLD SPEED,WmpSPEED,Wmp

AT LOW SPEEDS[MODE I] Eb IS SMALL, TIME FOR CURRENT AT LOW SPEEDS[MODE I] Eb IS SMALL, TIME FOR CURRENT IS LARGEIS LARGE

TO LIMIT CURRENT TO SAFE VALUES THE SWITCHES ARE TO LIMIT CURRENT TO SAFE VALUES THE SWITCHES ARE OPENED AND CLOSED SEQUENTIALLY LIKE CHOPPEROPENED AND CLOSED SEQUENTIALLY LIKE CHOPPER

AVERAGE TORQUE IS CONTROLLED BY AMPLITUDE OF AVERAGE TORQUE IS CONTROLLED BY AMPLITUDE OF CURRENTCURRENT

WORKS IN THIS MODE UPTO BASE SPEED,WmbWORKS IN THIS MODE UPTO BASE SPEED,Wmb

CONSTANT VOLTAGE DRIVE[CONSTANT POWER CONSTANT VOLTAGE DRIVE[CONSTANT POWER MODE]MODE]

CURRENT FORCED DRIVE[CONSTANT CURRENT FORCED DRIVE[CONSTANT POWER*SPEED MODE]POWER*SPEED MODE]

CHOPPER DRIVE [CONSTANT TORQUE MODE] CHOPPER DRIVE [CONSTANT TORQUE MODE]

FEATURESFEATURES ADVANTAGESADVANTAGES ROTOR HAS NO WINDINGS COMMUTATOR ROTOR HAS NO WINDINGS COMMUTATOR

OR BRUSH OR BRUSH

TORQUE –INERTIA RATIO IS HIGHTORQUE –INERTIA RATIO IS HIGH

HIGH RELIABILITY,WIDE SPEED RANGE,LOW COSTHIGH RELIABILITY,WIDE SPEED RANGE,LOW COST

FAST RESPONSE,RUGGEDNESS,FAULT TOLERANCEFAST RESPONSE,RUGGEDNESS,FAULT TOLERANCE

NO SHOOT THROUGH AND CROSS OVERS IN NO SHOOT THROUGH AND CROSS OVERS IN CONVERTERCONVERTER

NO PERMANENT MAGNETNO PERMANENT MAGNET

OC VOLTAGE AND SHORT CIRCUIT CURRENT AT OC VOLTAGE AND SHORT CIRCUIT CURRENT AT FAULTS IS ZEROFAULTS IS ZERO

DISADVANTAGESDISADVANTAGES

ROTOR POSITION SENSORS REQUIREDROTOR POSITION SENSORS REQUIRED

TORQUE RIPPLES ARE HIGHTORQUE RIPPLES ARE HIGH

ACOUSTIC NOISE IS PRESENTACOUSTIC NOISE IS PRESENT

APPLICATIONSAPPLICATIONS FLUID PUMPS,VACUUMFLUID PUMPS,VACUUM BLOWERSBLOWERS PROCESS CONTROL INDUSTRIESPROCESS CONTROL INDUSTRIES HYBRID/ELECTRIC VEHICLESHYBRID/ELECTRIC VEHICLES ELECTROMECHANICAL BRAKE SYSTEMELECTROMECHANICAL BRAKE SYSTEM ELECTRIC POWER STEERINGELECTRIC POWER STEERING STARTER GENERATOR SYSTEMSTARTER GENERATOR SYSTEM FUEL PUMP OPERATIONFUEL PUMP OPERATION