A reluctance motor is a type of electric motor that induces non-permanent magnetic poles on the ferromagnetic rotor. The rotor does not have any windings. It generates torque through magnetic reluctance. Reluctance motor sub types include synchronous, variable, switched and variable stepping. Reluctance motors can deliver high power density at low cost, making them attractive for many applications. Disadvantages include high torque ripple (the difference between maximum and minimum torque during one revolution) when operated at low speed, and noise due to torque ripple.

1. Reluctance Motor
Mr. C D Patil
Dept. of EE

2. • The SYNCHRONOUS RELUCTANCE MOTOR is an electrical
rotating machine that converts the electrical power into mechanical
power.
• The torque developed in the motor due to the difference in reluctances
is called reluctance torque.
• A synchronous motor in which only the reluctance torque is developed
is called synchronous reluctance motor (SyRM).
Synchronous Reluctance Motor

3. Construction of Synchronous Reluctance Motor
As construction and production
process the SRM is similar to the
Induction motors. Only the rotor
design has significant difference,
SRM rotor is unsymmetrical.

4. Construction of Synchronous Reluctance Motor
Mechanical construction of the rotor seems to be
quite simple since does not require
aluminum/copper casting or magnets assembly
but its design is complex due to the particular
“shape” of the rotor slots that must keep the
necessary robustness with a minimized
connection sectors between the rotor “poles”.

5. Construction of Synchronous Reluctance Motor
As construction and production process the SRM is similar to the
Induction motors. Only the rotor design has significant
difference, SRM rotor is unsymmetrical.

6. Working Prniciple of Synchronous Reluctance Motor
•Because the magnetic design of the rotor has
areas of high RELUCTANCE (white areas,
air) and areas of low RELUCTANCE (blue
areas, iron).
•The RELUCTANCE is a magnetic resistance
and is the opposite of the permeance.
•The rotor reluctance depends from the
“empty” areas present on the rotor laminations
that creates a kind of magnetic barrier where
the flux find high “resistance” to flow.

7. Working Prniciple of Synchronous Reluctance Motor

8. Working Prniciple of Synchronous Reluctance Motor

9. Advantages & Applications of Synchronous Reluctance Motor
 Advantages-
 No electromagnetic losses
 Mechanically strong
 Inherently reliable
 Simple construction
 Cheaper
 Higher efficiency
 Robust
 Applications
 Pumps or conveyers
 Synthetic fiber manufacturing industries
 Wrapping and folding machines
 Nuclear reactors
 Synchronized textile drives
 Processing of continuous sheet or film material
 Constant speed applications

10. Switched Reluctance Motor
• Switched Reluctance Motor (SRM) is also known as Variable
Reluctance Motor. This motor works on the principle of
variable reluctance. This means, the rotor always tries to align
along the lowest reluctance path.
• As the name suggests, a switching inverter is required for the
operation of Switched Reluctance Motor.

11. Construction of Switched Reluctance Motor
• Variable Reluctance Motor or Switched Reluctance Motor has
two different constructions: Singly Salient Construction and
Doubly Salient Construction.
• Stator and rotor magnetic circuits are laminated to reduce the
core losses in both type of SRM.

12. Construction of Switched Reluctance Motor
• A singly salient construction SRM consist of a non-
salient stator and a salient two pole rotor.
• The rotor do not have any winding wound over it but the
stator have two phase winding as shown in figure.
• It should be noted that, in actual SRM the number of
phase winding on stator may be more than two.
• Since the rotor is of salient construction, the inductance
of stator phase winding varies with the rotor position.
• The inductance is minimum when the rotor axis and
stator phase winding axis coincides whereas it is
maximum when both the axis are in quadrature.

13. Construction of Switched Reluctance Motor
• Doubly Salient Construction:
• Unlike singly salient type, the stator of doubly salient
Switched Reluctance Motor is of salient construction and
consists of four poles as shown in figure.
• The rotor do not carry any winding and is of salient
construction but have two poles. Thus this type of SRM is
a hetropolar motor where the numbers of stator and rotor
poles are not same.
• The stator phase windings are concentrated winding.
• These concentrated windings on radially opposite poles
are either connected in series or parallel to result into two
phase winding on stator.
• A doubly salient type Switched Reluctance Motor or
variable Reluctance Motor produces more torque as
compared to singly salient type for the same size.
Therefore a doubly SRM is more common and widely
used.

14. Working principle of Switched Reluctance Motor
• As we know that magnetic flux have a tendency to
flow through lowest reluctance path, therefore rotor
always tends to align along the minimum reluctance
path. This is the basic working principle of Switched
Reluctance Motor or Variable Reluctance Motor.
• Therefore, when stator phase winding A is energized,
the rotor align along this phase as shown in figure 1.
• When stator phase winding A is de-energized and
winding B is energized, the rotor align itself along B
phase as shown in figure 2.

15. Working principle of Switched Reluctance Motor
• Similarly, the rotor occupies a position along phase
winding C when this phase is energized.
• Thus rotor rotation in clockwise direction is achieved
by energizing the phase winding in a ABC sequence.
If rotor rotation in anti-clockwise direction is require,
stator phase winding must be energized in ACB
sequence.
• It must also be noted that, a particular phase winding
must be energized / de-energized in synchronism
with rotor position. This means as soon as the rotor
align along the A phase, B phase must be energized
and A phase must be de-energized if clockwise rotor
rotation is required.

16. Characteristics of Switched Reluctance Motor

17. Applications of Switched Reluctance Motor
• Switched reluctance motor (SRM) is gaining much interest in
industrial applications such as wind energy systems and electric
vehicles due to its simple and rugged construction, high‐speed
operation ability, insensitivity to high temperature, and its
features of fault tolerance.

18. Construction of Permanent Magnet Synchronous Motor (PMSM)
• The basic construction of PMSM is same as that of synchronous motor.
• The only difference lies with the rotor. Unlike synchronous motor, there is no filed
winding on the rotor of PMSM.
• Field poles are created by using permanent magnet.
• These Permanent magnets are made up of high permeability and high coercivity
materials like Samarium-Cobalt and Neodium-Iron-Boron. Neodium-Iron-Boron is
mostly used due to its ease of availability and cost effectiveness. Theses permanent
magnets are mounted on the rotor core.
• Based on the mounting arrangement of magnet on rotor core, Permanent Magnet
Synchronous Motor (PMSM) can be categorized into two types: Surface Mounted
PMSMs and Buried or interior PMSMs.

19. Construction of Permanent Magnet Synchronous Motor (PMSM)
•Surface Mounted PMSM, permanent magnet is
mounted on the rotor surface as shown in figure.
•This type of PMSM is not robust and therefore not
suited for high speed application. Since the permeability
of magnet and air gap is almost same, therefore this type
of construction provides a uniform air gap.
•Therefore, there is no reluctance torque present. Thus
the dynamic performance of this motor is superior and
hence used in high performance machine tool drives and
robotics.

20. Construction of Permanent Magnet Synchronous Motor (PMSM)
•In Interior or Buried PMSM, the permanent magnets are
embedded into the rotor instead of mounting on the surface.
This provides robustness and hence can be used in high
speed applications. Due to presence of saliency, reluctance
torque is present in this type of PMSM.

21. Working Principle of Permanent Magnet Synchronous Motor (PMSM)
• The working principle of permanent magnet synchronous motor is same as that of synchronous
motor.
• When three phase winding of stator is energized from 3 phase supply, rotating magnetic field is
set up in the air gap.
• At synchronous speed, the rotor field poles locks with the rotating magnetic field to produce
torque and hence rotor continues to rotate.
• As we know that synchronous motors are not self starting, PMSM needs to be started somehow.
Since there is no winding on the rotor, induction windings for starting is not applicable for such
motors and therefore variable frequency power supply for this purpose.
 Applications:
• Permanent Magnet Synchronous Motor can be used as an alternative for servo drives. It is
widely used in various industrial application viz. robotics, traction, aerospace etc.