21-02-2010, 11:33 AM
[attachment=2378]
SWITCHED RELUCTANCE MOTORS
HISTORY
INVENTED BY DAVIDSON OF SCOTLAND IN 1838
WAL`KER INVENTED VARIABLE RELUCTANCE MOTOR IN 1920
BEDFORD AND HOFT FILED US PATENTS ON SRM IN 1971
HEWLETT PACKARD- USED SRM IN VOLUME APPLICATION (DRAFTMASTER PLOTTER)
INTRODUCTION
Pple of stepper motor; magn material suspended in magn field align in direction of field due to torque
Basically stepper motor;i.e rotate through fixed angle [step angle] when input pulse is applied
Speed proportional to pulse frequency; pulse<200Hz-discrete rotation and pulse>16KHz-continous rotation
When step angle decreases,num of steps / rev increases
Stepper motors:#sr motors #pm motors #hybrid motors
PRIMARY CHOICE FOR SERVO APPLICATIONS
SIMPLE MOTOR CONSTRUCTION AND POWER CONVERTER MADE IT ATTRACTIVE ALTERNATIVE TO INDUCTION MACHINES
LIKE AC MACHINES,SRM DONOT REQUIRE COMMUTATOR AND BRUSHES
HIGH PEAK TORQUE,POWER DENSITY,TORQUE INERTIA RATIO
VARIABLE SPEED MACHINE
PRINCIPLE
MAGNETIC RESISTANCE OR RELUCTANCE
PRINCIPLE OF RELUCTANCE MOTOR
MAGNETIC FIELD CAUSES MAGNETIC CURRENT TO FOLLOW ALONG A PATH OF LEAST RELUCTANCE
HOPKINSONâ„¢S LAW,
R=MMF/FLUX,
R-RELUCTANCE(AMP-TURNS/WB)
F-MMF(AMP-TURNS)
FLUX,WEBERS
AIR AND VACUUM HAVE HIGH RELUCTANCE,
SOFT IRON HAS MINIMUM RELUCTANCE
CONC OF FLUX FORM TEMP POLES AND ATTRACT
R=L/UoUrA
RELUCTANCE MOTOR IS SALIENT POLE SYNCHRONOUS MOTOR WITH NO FIELD WINDINGS
WHEN ARMATURE COILS ARE EXCITED, ROTOR ALIGNS IN THE DIRECTION OF MINIMUM RELUCTANCE[RELUCTANCE TORQUE]
T=3V2[Xd-Xq]Sin2{LOAD ANGLE}
2wXdXq
V
ER PHASE RMS VOLTAGE
W=SYNC SPEED RAD/SEC
Xd
IRECT AXIS RELUCTANCE
Xq: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
DIAMETRICALLY OPPOSITE ARMATURE WINDINGS ARE CONNECTED TO FORM A PHASE
FOR BIDERCTIONAL CONTROL AND SELF STARTING,NUM OF ROTOR POLES ARE LESS THAN NUM OF STATOR POLES
M15,M17,M19 FOR HIGH SPEED AND HYPERCO AND VANADIUM PERMENDUR FOR HIGH PERFORMANCE
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
FOR MULTI STACK OPERATION,NUM OF ROTOR AND STATOR DEPENDS ON NUM OF PHASES
POSITION OF MIN RELUCTANCE CHANGED WITH HELP OF POSITION SENSORS
WHEN PHASE IS EXCITED AFTER THE ROTOR PASSES POINT OF MIN RELUCTANCE, REVERSE TORQUE ACTS[REGENERATIVE BRAKING]
TORQUE CHARACTERISTICS
DUE TO SALIENCY OF STATOR AND ROTOR,INDUCTANCE IS A FUNCTION OF ROTOR POSITION
A 6 ROTOR MACHINE HAS 6 MAX AND MIN VALUES OF INDUCTANCE
IF APPLIED INPUT IS V,
V{inst}=Ri+Ldi/dt +WmidL/d0
BACK EMF,e=WmidL/do
i V{inst}=Ri2+d(Li2/2)/dt +Wmi2dL/d0
T=i2/2dL/dO
INPUT=WINDING HEAT LOSS+RATE OF CHANGE OF STORED MAGNETIC ENERGY+MECH POWER OUTPUT
4-QUAD OPERATION IS POSSIBLE BY ADJUSTING TIME OF INPUT PULSE
IF INPUT IS DURING POSITIVE SLOPE OF L/ROTOR ANGLE PLOT POSITIVE TORQUE;I AND IV QUAD OPERATION
IF INPUT IS DURING NEGATIVE SLOPE NEGATIVE TORQUE;II AND III QUAD OPERATION
POSITION SENSORS ARE REQUIRED TO KNOW THE ANGLE AT WHICH INPUT IS TO BE PROVIDED
MODES OF OPERATION
CONSTANT TORQUE MODE[CURRENT CONTROL
CONSTANT POWER MODE[ANGLE CONTROL]
CONSTANT POWER*SPEED MODE[FORCEDCURRENT CONTROL WITH EXTERNAL RESISTANCE]
WITH SOURCE VOLTAGE CONSTANT,Eb INCREASES WITH SPEED ENOUGH TIME IS NOT AVAILABLE FOR CURRENT TO DEVELOP
IN MODE II :WINDING IS CONNECTED TO SOURCE EARLIER THAN ANGLE AT WHICH INDUCTANCE BEGINS TO RISE
CURRENT REACHES MAX VALUE;Eb INCREASES HENCE CURRENT BEGINS TO FALL
DUE TO CONSTANT DC SOURCE, FLUX INCREASES UNIFORMLY UNTIL CURRENT IS REVERSED AFTER WHICH FLUX DECREASES UNIFORMLY
HENCE CURRENT AND FLUX BECOMES ZERO WHEN NEGATIVE CYCLE OF VOLTAGE IS COMPLETED
OPERATES IN THIS MODE UPTO UPPER THRESHOLD SPEED,Wmp
AT LOW SPEEDS[MODE I] Eb IS SMALL, TIME FOR CURRENT IS LARGE
TO LIMIT CURRENT TO SAFE VALUES THE SWITCHES ARE OPENED AND CLOSED SEQUENTIALLY LIKE CHOPPER
AVERAGE TORQUE IS CONTROLLED BY AMPLITUDE OF CURRENT
WORKS IN THIS MODE UPTO BASE SPEED,Wmb
CONVERTER SYSTEM
BRIDGE CONVERTER USED PER PHASE
WHEN Q1 AND Q2 CLOSED CURRENT FLOWS THROUGH SWITCHES AND PHASE
WHEN Q1 OPEN AND Q2 CLOSED;CURRENT FREEWHEELS THROUGH D1 BACK TO SOURCE
WHEN BOTH Q1 AND Q2 OPEN CURRENT FREEWHEELS THROUGH D1 AND D2
DEPENDING ON MODE OF OPERATION 3 DRIVE CIRCUITS ARE USED
CONSTANT VOLTAGE DRIVE[CONSTANT POWER MODE]
CURRENT FORCED DRIVE[CONSTANT POWER*SPEED MODE]
CHOPPER DRIVE [CONSTANT TORQUE MODE]
FEATURES
ADVANTAGES
ROTOR HAS NO WINDINGS COMMUTATOR OR BRUSH
TORQUE “INERTIA RATIO IS HIGH
HIGH RELIABILITY,WIDE SPEED RANGE,LOW COST
FAST RESPONSE,RUGGEDNESS,FAULT TOLERANCE
NO SHOOT THROUGH AND CROSS OVERS IN CONVERTER
NO PERMANENT MAGNET
OC VOLTAGE AND SHORT CIRCUIT CURRENT AT FAULTS IS ZERO
DISADVANTAGES
ROTOR POSITION SENSORS REQUIRED
TORQUE RIPPLES ARE HIGH
ACOUSTIC NOISE IS
APPLICATIONS
FLUID PUMPS,VACUUM BLOWERS
PROCESS CONTROL INDUSTRIES
HYBRID/ELECTRIC VEHICLES
ELECTROMECHANICAL BRAKE SYSTEM
ELECTRIC POWER STEERING
STARTER GENERATOR SYSTEM
FUEL PUMP OPERATION
SWITCHED RELUCTANCE MOTORS
HISTORY
INVENTED BY DAVIDSON OF SCOTLAND IN 1838
WAL`KER INVENTED VARIABLE RELUCTANCE MOTOR IN 1920
BEDFORD AND HOFT FILED US PATENTS ON SRM IN 1971
HEWLETT PACKARD- USED SRM IN VOLUME APPLICATION (DRAFTMASTER PLOTTER)
INTRODUCTION
Pple of stepper motor; magn material suspended in magn field align in direction of field due to torque
Basically stepper motor;i.e rotate through fixed angle [step angle] when input pulse is applied
Speed proportional to pulse frequency; pulse<200Hz-discrete rotation and pulse>16KHz-continous rotation
When step angle decreases,num of steps / rev increases
Stepper motors:#sr motors #pm motors #hybrid motors
PRIMARY CHOICE FOR SERVO APPLICATIONS
SIMPLE MOTOR CONSTRUCTION AND POWER CONVERTER MADE IT ATTRACTIVE ALTERNATIVE TO INDUCTION MACHINES
LIKE AC MACHINES,SRM DONOT REQUIRE COMMUTATOR AND BRUSHES
HIGH PEAK TORQUE,POWER DENSITY,TORQUE INERTIA RATIO
VARIABLE SPEED MACHINE
PRINCIPLE
MAGNETIC RESISTANCE OR RELUCTANCE
PRINCIPLE OF RELUCTANCE MOTOR
MAGNETIC FIELD CAUSES MAGNETIC CURRENT TO FOLLOW ALONG A PATH OF LEAST RELUCTANCE
HOPKINSONâ„¢S LAW,
R=MMF/FLUX,
R-RELUCTANCE(AMP-TURNS/WB)
F-MMF(AMP-TURNS)
FLUX,WEBERS
AIR AND VACUUM HAVE HIGH RELUCTANCE,
SOFT IRON HAS MINIMUM RELUCTANCE
CONC OF FLUX FORM TEMP POLES AND ATTRACT
R=L/UoUrA
RELUCTANCE MOTOR IS SALIENT POLE SYNCHRONOUS MOTOR WITH NO FIELD WINDINGS
WHEN ARMATURE COILS ARE EXCITED, ROTOR ALIGNS IN THE DIRECTION OF MINIMUM RELUCTANCE[RELUCTANCE TORQUE]
T=3V2[Xd-Xq]Sin2{LOAD ANGLE}
2wXdXq
V
ER PHASE RMS VOLTAGEW=SYNC SPEED RAD/SEC
Xd
IRECT 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
DIAMETRICALLY OPPOSITE ARMATURE WINDINGS ARE CONNECTED TO FORM A PHASE
FOR BIDERCTIONAL CONTROL AND SELF STARTING,NUM OF ROTOR POLES ARE LESS THAN NUM OF STATOR POLES
M15,M17,M19 FOR HIGH SPEED AND HYPERCO AND VANADIUM PERMENDUR FOR HIGH PERFORMANCE
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
FOR MULTI STACK OPERATION,NUM OF ROTOR AND STATOR DEPENDS ON NUM OF PHASES
POSITION OF MIN RELUCTANCE CHANGED WITH HELP OF POSITION SENSORS
WHEN PHASE IS EXCITED AFTER THE ROTOR PASSES POINT OF MIN RELUCTANCE, REVERSE TORQUE ACTS[REGENERATIVE BRAKING]
TORQUE CHARACTERISTICS
DUE TO SALIENCY OF STATOR AND ROTOR,INDUCTANCE IS A FUNCTION OF ROTOR POSITION
A 6 ROTOR MACHINE HAS 6 MAX AND MIN VALUES OF INDUCTANCE
IF APPLIED INPUT IS V,
V{inst}=Ri+Ldi/dt +WmidL/d0
BACK EMF,e=WmidL/do
i V{inst}=Ri2+d(Li2/2)/dt +Wmi2dL/d0
T=i2/2dL/dO
INPUT=WINDING HEAT LOSS+RATE OF CHANGE OF STORED MAGNETIC ENERGY+MECH POWER OUTPUT
4-QUAD OPERATION IS POSSIBLE BY ADJUSTING TIME OF INPUT PULSE
IF INPUT IS DURING POSITIVE SLOPE OF L/ROTOR ANGLE PLOT POSITIVE TORQUE;I AND IV QUAD OPERATION
IF INPUT IS DURING NEGATIVE SLOPE NEGATIVE TORQUE;II AND III QUAD OPERATION
POSITION SENSORS ARE REQUIRED TO KNOW THE ANGLE AT WHICH INPUT IS TO BE PROVIDED
MODES OF OPERATION
CONSTANT TORQUE MODE[CURRENT CONTROL
CONSTANT POWER MODE[ANGLE CONTROL]
CONSTANT POWER*SPEED MODE[FORCEDCURRENT CONTROL WITH EXTERNAL RESISTANCE]
WITH SOURCE VOLTAGE CONSTANT,Eb INCREASES WITH SPEED ENOUGH TIME IS NOT AVAILABLE FOR CURRENT TO DEVELOP
IN MODE II :WINDING IS CONNECTED TO SOURCE EARLIER THAN ANGLE AT WHICH INDUCTANCE BEGINS TO RISE
CURRENT REACHES MAX VALUE;Eb INCREASES HENCE CURRENT BEGINS TO FALL
DUE TO CONSTANT DC SOURCE, FLUX INCREASES UNIFORMLY UNTIL CURRENT IS REVERSED AFTER WHICH FLUX DECREASES UNIFORMLY
HENCE CURRENT AND FLUX BECOMES ZERO WHEN NEGATIVE CYCLE OF VOLTAGE IS COMPLETED
OPERATES IN THIS MODE UPTO UPPER THRESHOLD SPEED,Wmp
AT LOW SPEEDS[MODE I] Eb IS SMALL, TIME FOR CURRENT IS LARGE
TO LIMIT CURRENT TO SAFE VALUES THE SWITCHES ARE OPENED AND CLOSED SEQUENTIALLY LIKE CHOPPER
AVERAGE TORQUE IS CONTROLLED BY AMPLITUDE OF CURRENT
WORKS IN THIS MODE UPTO BASE SPEED,Wmb
CONVERTER SYSTEM
BRIDGE CONVERTER USED PER PHASE
WHEN Q1 AND Q2 CLOSED CURRENT FLOWS THROUGH SWITCHES AND PHASE
WHEN Q1 OPEN AND Q2 CLOSED;CURRENT FREEWHEELS THROUGH D1 BACK TO SOURCE
WHEN BOTH Q1 AND Q2 OPEN CURRENT FREEWHEELS THROUGH D1 AND D2
DEPENDING ON MODE OF OPERATION 3 DRIVE CIRCUITS ARE USED
CONSTANT VOLTAGE DRIVE[CONSTANT POWER MODE]
CURRENT FORCED DRIVE[CONSTANT POWER*SPEED MODE]
CHOPPER DRIVE [CONSTANT TORQUE MODE]
FEATURES
ADVANTAGES
ROTOR HAS NO WINDINGS COMMUTATOR OR BRUSH
TORQUE “INERTIA RATIO IS HIGH
HIGH RELIABILITY,WIDE SPEED RANGE,LOW COST
FAST RESPONSE,RUGGEDNESS,FAULT TOLERANCE
NO SHOOT THROUGH AND CROSS OVERS IN CONVERTER
NO PERMANENT MAGNET
OC VOLTAGE AND SHORT CIRCUIT CURRENT AT FAULTS IS ZERO
DISADVANTAGES
ROTOR POSITION SENSORS REQUIRED
TORQUE RIPPLES ARE HIGH
ACOUSTIC NOISE IS
APPLICATIONS
FLUID PUMPS,VACUUM BLOWERS
PROCESS CONTROL INDUSTRIES
HYBRID/ELECTRIC VEHICLES
ELECTROMECHANICAL BRAKE SYSTEM
ELECTRIC POWER STEERING
STARTER GENERATOR SYSTEM
FUEL PUMP OPERATION