Switched Reluctance Motor - Principle Of Operation

Reluctance motors – principle of operation –
torque equation – torque slip characteristics-
applications. Switched reluctance motors –
principle of operation – power converter
circuits – torque equation – different types –
comparison – applications.

1. Switched Reluctance Motor

2. Reluctance motors – principle of operation –
torque equation – torque slip characteristics-
applications. Switched reluctance motors –
principle of operation – power converter
circuits – torque equation – different types –
comparison – applications.

3. Characteristic features of SRM
•Low cost (no permanent magnet)
•Torque-inertia ratio: High
•Simple construction & Robust
•High tolerance
•High efficiency
•Max operating speed
•Similar to Variable reluctance stepper motor –
closed loop; rotor position feedback

4. SRM Disadvantages
•ROTOR POSITION SENSORS REQUIRED
•TORQUE RIPPLES ARE HIGH
•ACOUSTIC NOISE IS PRESENT

5. SRM Applications
•General purpose industrial drives;
•Application-specific drives: compressors, fans,
pumps, centrifuges;
•Domestic drives: food processors, washing
machines, vacuum cleaners;
•Electric vehicle application;
•Aircraft applications;
•Servo-drive.

6. SRM Principle
•reluctance torque into mechanical power
•both the stator and rotor - salient-pole; high O/p
torque
•no windings or permanent magnets or
commutator, brush on the rotor
•torque is produced by the alignment tendency of
poles
•rotor will shift to a position where reluctance is to
be minimized and thus the inductance of the
excited winding is maximized

7. SRM Types

8. SRM Construction
One tooth
per pole
(6/4, 8/6)





Two teeth
Per pole
(12/10)

9. SRM Driving System

10. Magnetic circuit of SRM
Rotor position of two pole SRM Inductance Profile
where βs and βr
are stator and
rotor pole arcs,
respectively
Pr is the number of
rotor poles

11. Inductance Profile
•Four Regions:
•0 − θ1 and θ4 − θ5:
–stator and rotor poles are not overlapping
–flux is determined by the air path
–inductance minimum; unaligned inductance, Lu
–NO torque production
•θ1 − θ2:
–stator and rotor poles are overlapping
–flux pass through stator-rotor laminations
–increasing inductance, positive slope
–current impressed in the winding; positive torque
–This region comes to an end when the overlap of poles is complete

12. Inductance Profile…
•θ2 − θ3:
–Movement of rotor; but stator and rotor overlap
–flux passes through stator and rotor poles
–inductance maximum, aligned inductance, La
–Maximum torque
•θ3 − θ4:
–rotor pole is moving away from overlapping the stator pole
–flux is determined by the air path, similar to θ1 − θ2 region
–Decreasing inductance, negative slope
–negative torque production

13. Inductance and Torque

14. Inductance and Torque

15. Torque-Speed Characteristics

16. SRM Working

17. Power Converters

18. Power Converters

19. Power Converters
•Asymmetric bridge
(2q switch)





•1.5 q switch

20. Power Converters
•R-dump (q switch)

21. Power Converter
•C-dump converter
(q+1 switch)

22. Power Converter
•(q+1) switching topology (shared switch)

23. Power Converter
•Bifilar type
(q switch)

24. Voltage and Torque Eqn.

25. Voltage and Torque Eqn.

26. Voltage and Torque Eqn.

27. Microprocessor based control of SRM