1. SWITCHED RELUCTANCE MOTORS  10/2/2018 11  U P KUMAR CHATURVEDULA

2. 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) 22  10/2/2018  U P KUMAR CHATURVEDULA

3. INTRODUCTION Principle of stepper motor; magnetic material suspended in magnetic 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 16KHz- continous rotation When step angle decreases, number of steps / rev increases Stepper motors:#sr motors #pm motors #hybrid motors  10/2/2018 33  U P KUMAR CHATURVEDULA

4. Why SRM? PRIMARY CHOICE FOR SERVO APPLICATIONS LIKE AC MACHINES,SRM DO NOT REQUIRE COMMUTATOR AND BRUSHES HIGH PEAK TORQUE,POWER DENSITY,TORQUE INERTIA RATIO VARIABLE SPEED MACHINE  10/2/2018 44  U P KUMAR CHATURVEDULA

5. 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=3V 2 [Xd-Xq]Sin2{LOAD ANGLE} 2wXdXq V:PER PHASE RMS VOLTAGE W=SYNC SPEED RAD/SEC Xd:DIRECT AXIS RELUCTANCE Xq:QUAD AXIS RELUCTANCE  10/2/2018 55  U P KUMAR CHATURVEDULA

6. 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  10/2/2018 66  U P KUMAR CHATURVEDULA

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8. 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  10/2/2018 88  U P KUMAR CHATURVEDULA

9. VARIATION OF L  10/2/2018  U P KUMAR CHATURVEDULA 99

10. 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=W m idL/do i V{inst}=Ri 2 +d(Li 2 /2)/dt +Wmi 2 dL/d0 T=i 2 /2dL/dO INPUT=WINDING HEAT LOSS+RATE OF CHANGE OF STORED MAGNETIC ENERGY+MECH POWER OUTPUT  10/2/2018  10  U P KUMAR CHATURVEDULA

11. L-Q PROFILE  10/2/2018  U P KUMAR CHATURVEDULA  11  For 0 < q < b s, the inductance rises from Lmin to Lmax.  For b s < q < b r, the inductance remains constant. This angle b r –b s is called dwell angle.  For b r < q < th inductance starts decreasing and reaches L min at q = For

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13. MODES OF OPERATION CONSTANT TORQUE MODE[CURRENT CONTROL CONSTANT POWER MODE[ANGLE CONTROL] CONSTANT POWER*SPEED MODE[FORCED CURRENT CONTROL WITH EXTERNAL RESISTANCE] WITH SOURCE VOLTAGE CONSTANT, Eb INCREASES WITH SPEED ENOUGH TIME IS NOT AVAILABLE FOR CURRENT TO DEVELOP  10/2/2018  13  U P KUMAR CHATURVEDULA

14. 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  10/2/2018  14  U P KUMAR CHATURVEDULA

15. 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  10/2/2018  15  U P KUMAR CHATURVEDULA

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18. CONSTANT VOLTAGE DRIVE[CONSTANT POWER MODE] CURRENT FORCED DRIVE[CONSTANT POWER*SPEED MODE] CHOPPER DRIVE [CONSTANT TORQUE MODE]  10/2/2018  18  U P KUMAR CHATURVEDULA

19. FEATURES ADVANTAGES ROTOR HAS NO WINDINGS COMMUTATOR OR BRUSHES 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  10/2/2018  19  U P KUMAR CHATURVEDULA

20. DISADVANTAGES ROTOR POSITION SENSORS REQUIRED TORQUE RIPPLES ARE HIGH ACOUSTIC NOISE IS PRESENT  10/2/2018  20  U P KUMAR CHATURVEDULA

21. APPLICATIONS FLUID PUMPS,VACUUM BLOWERS PROCESS CONTROL INDUSTRIES HYBRID/ELECTRIC VEHICLES ELECTROMECHANICAL BRAKE SYSTEM ELECTRIC POWER STEERING STARTER GENERATOR SYSTEM FUEL PUMP OPERATION  10/2/2018  21  U P KUMAR CHATURVEDULA