Special machine type

1. SYNCHRONOUS RELUCTANCE MOTOR

2. Unit – II
SYNCHRONUS RELUCTANCE MOTOR
Unit Syllabus
Constructional features, operating principle and
characteristics of synchronous reluctance motor

3. Reluctance Motors
• An induction motor with a modified squirrel-
cage rotor
– Single-phase or Three-phase
– rotor turns in synchronism with the rotating
magnetic flux

4. What is synchronous reluctance
motor?
• Stator consists of multiple salient (ie.
projecting) electromagnet poles, similar to a
wound field brushed DC motor
• Ferromagnetic rotor(non-permanent magnetic
poles)
• Torque is generated through the phenomenon
of magnetic reluctance.
• The rotor consists of soft magnetic material,
such as laminated silicon steel, which has
multiple projections acting as salient magnetic
poles through magnetic reluctance.
• Number of rotor poles is less than the number
of stator poles, which minimizes torque ripple.

6. Construction

7. Construction

9. Types based on magnetization
• Radial Type
• Axial type

10. Flux barrier type

11. Distributed Anisotropy cage motors

12. Axially laminated Anisotropic rotor

13. Types of Rotor
Three different types of SynRM with anisotropic rotor structures
a) Simple salient pole (SP) rotor
b) Axially laminated rotor
c) Transversally laminated rotor

14. Simple salient pole (SP) rotor
• The salient pole rotor is
made by removing some
iron material in the
transversal region.
Four-pole conventional
salient pole design

15. Axially laminated rotor
• In the axially laminated rotor,
the laminations (iron) are
suitably shaped at each pole
and insulated from each
other using electrically and
magnetically passive
materials (insulation) and the
resulting stacks are
connected through pole
holders to the central region
to which the shaft is
connected. Four-pole axially-laminated
rotor design

16. Transversally laminated rotor
(Mostly Employed)
• In the third type of rotor
the laminations are
punched in the traditional
way. Thin ribs are left when
punching, thus the various
rotor segments are
connected to each other by
these ribs.
Four-pole transversally-laminated
rotor design

17. AXIAL TYPE RADIAL TYPE
Axially laminated rotor Radially laminated rotor
By increasing the Ld/Lq ratio, we
obtain more PF and efficiency
By decreasing Ld/Lq ratio,
circulating flux in the rotor pole
faces
Designed to have high saliency Designed to have optimized flux
guide
Offers good performance, torque,
PF, efficiency
To obtain less ripple torque, less
iron losses it is designed
Rotor has 2 designs Rotor has 1 design
Shaft may be rectangular cross
section
Shaft may be circular cross
section
High speed applications Poor choice for high speed
applications

18. Operating Principle
When a stator pole is energized, the rotor torque
is in the direction that will reduce reluctance.
Thus the nearest rotor pole is pulled into
alignment with the stator field (a position of less
reluctance).
In order to sustain rotation, the stator field must
rotate in advance of the rotor poles, thus
constantly "pulling" the rotor along.

19. Operation
• Rotor accelerates towards synchronous speed
• At a “critical” speed, the low-reluctance paths provided by
the salient poles will cause them to “snap” into
synchronism with the rotating flux.

20. Operation (continued)
• When the rotor synchronizes,
slip is equal to zero
• Rotor pulled around by
“reluctance torque”
• Figure at right shows the rotor
synchronized at no load

21. Operation (continued)
• A “step” increase in load
slows the rotor down, and
the rotor poles “lag” the
stator poles.
• The angle of lag, δ, is called
the “torque angle”.
• The maximum torque angle,
δmax = 45°.

22. Operation at maximum load
• Maximum load is when δ
= 45°.
• If load increases so that
δ>45°, the flux path is
“over stretched” and the
rotor falls out of
synchronism.
• Motor runs at slip speed

23. Reluctance torque, Trel
0
2
sin(2 )srel rel
V
T K
f

 
  
 
Trel = average value of reluctance torque
V = applied voltage (V)
f = line frequency (Hz)
δrel = torque angle (electrical degrees)
K = motor constant

24. Reluctance torque, Trel
• Maximum reluctance torque, Trelmax occurs at
δrel = 45°

25. Characteristics of synchronous
reluctance motor
The synchronous reluctance motor is not self
starting without the squirrel cage.
During run up it behaves as an induction
motor but as it approaches synchronous
speed, the reluctance torque takes over and
the motor locks into synchronous speed.

26. Torque - Angle characteristics

27. Torque – Speed Characteristics

28. Advantage & Disadvantage of SyRM
Advantages of SyRM
1. There is no concern with demagnetization, hence
synchronous reluctance.
2. There need be no excitation field at zero torque, thus
eliminating electromagnetic spinning losses.
3. SyRM rotor can be constructed entirely from high
strength, low cost materials.
4. Lower torque ripple.
Disadvantages of SyRM
1. Compared to induction motor it is slightly heavier and
has low power factor.
2. High cost than induction motor.
3. Need speed synchronization to inverter output
frequency by using rotor position sensor and sensor less control.

29. Applications of syrm
1. Synthetic fiber manufacturing equipment
2. Wrapping and folding machine
3. Auxiliary time mechanism
4. Synchronized conveyors
5. Metering pumps