SYNCHRONOUS RELUCTANCE MOTOR

Syllabi

Types

Axial and Transverse laminated motors

Operating principle

Reluctance

Phasor diagram

Characteristics

Vernier motor

Classification of AC Motors

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

Simple salient pole (SP) rotor

The salient pole rotor as the first possibility is

made by removing some

iron material from each

rotor in the transversal

region.

Four-pole conventional salient pole design

Axially laminated rotor

In the axially laminated rotor, which is the second type of SynRM, 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

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

Permanent magnet assisted SynRM

When PMs are inserted into the rotor flux barriers of a synchronous reluctance motor, it becomes a permanent magnet assisted synchronous reluctance motor (Pma-SynRM). PMs can be mounted in the rotor core of the axially or transversally laminated structure.

The polarity of magnets is chosen such that counteract the q-axis flux of the SynRM at rated load Four-pole transversally-laminated PM

assisted rotor design

Reluctance

Magnetic reluctance, or magnetic resistance, is a concept used in the analysis of magnetic circuits.

It is analogous to resistance in an electrical circuit, but rather than dissipating electric energy it stores

magnetic energy.

Magnetic field causes magnetic flux to follow the path of least magnetic reluctance.

What is synchronous reluctance motor?

A reluctance motor is a type of synchronous electric 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.

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 from the unaligned position 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. commutation gives significant control advantages for motor starting, speed control.

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.

Phasor Diagram

m

m

m

2sd sq

m sd sq

P =3VIcos

PT=

X -X3VT=

X *X

Applications of syrm

1. Synthetic fiber manufacturing equipment

2. Wrapping and folding machine

3. Auxiliary time mechanism

4. Synchronized conveyors

5. Metering pumps

Advantage & Disadvantage of SyRM

Advantages of SyRM1. 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 SyRM1. 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.

Vernier Motor

It is an unexcited reluctance type sync.motor.

The peculiar feature of this motor is that a small displacement of the rotor produces a large displacement of the axis of maximum and minimum permeance.

A Vernier Motor is an unexcited reluctance type Synchronous motor which has the feature of high torque at low speed

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