Unit-I Synchronous Reluctance Motor (SyncREL)

Unit-I Synchronous Reluctance Motor

(SyncREL)

by

Sakthisudhursun B.

Assistant Professor

Department of Electrical and Electronics Engineering,

Mepco Schlenk Engineering College,

Sivakasi www.vidyarthiplus.com

www.Vidyarthiplus.com

Why in recent days reluctance machines are popular?

• Simple and Robust construction

• No copper loss

• No requirement of permanent magnet

• Less initial cost

• Stator can be easily cooled

Commercial introduction: ABB

Power rating available: 17kW to 350kW

Introduction

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Advantages over Permanent Magnet Machines:

• No permanent magnet is used hence reduces the over all initial

cost

• It can operate at extremely high temperature & speed

Limitation over Permanent Magnet Machines:

• High KVA rating of the converter

• Power factor and efficiency is not as high as Permanent magnet

machines

Introduction



Reluctance Machine

Switched Reluctance

Machine (SRM)

Synchronous Reluctance

Machine (Syncrel)

Types of Reluctance Machine



SRM Syncrel

Double Salient structure (i.e.) Both stator and Rotor has Salient structure

Only Rotor has Salient structure

New stator structure hence initial cost is more to make

Standard 3-phase induction machine stator can be used

Concentrated Winding Sine distributed winding

Special converter required to drive SRM

Conventional inverter is required to drive Syncrel

Difficult to modeling due to non linearity in both stator and rotor

Normal AC machine modeling can be applied

Torque pulsation is more Relatively smoothed torque is produced

Relatively difficult to control due to non linearity

Easy to control

Comparison between SRM & SYNCREL



Torque generation in Salient Pole Synchronous machine:

1) Electromagnetic torque

2) Reluctance torque

Electromagnetic Torque:

Due to the interaction between magnetic field produced by rotor & armature current

Reluctance Torque:

Due to the difference between the direct axis and quadrature axis reactance

What is a synchronous reluctance (SYNCREL) motor?

SYNCREL is a synchronous motor in which the torque is produced only due

to the difference between the direct axis and quadrature axis reactance

Synchronous Reluctance Motor (SyncREL)

2sin

X2X

XXVsin

X

VE3T

qd

qd2

d





Construction

Stator & Rotor



Stator:

• Armature or stator core is made of ferromagnetic material and laminated

Why?

• To reduce the hysteresis and eddy current losses

• Stator core is attached to the stator frame

• Slots for housing the armature winding are provided along the inner

periphery of stator core

• Semi-closed slots are used

• Stator carries three-phase winding and arranged for required number of

poles

• Distributed windings are used

Construction



Rotor:

• Rotor is constructed in such a way that the armature inductance varies

sinusoidally

• Inductance should be maximum along direct axis & minimum along

quadrature axis

• Difference between direct axis & quadrature axis inductance should be as

large as possible

Why?

• To generate the maximum torque

Different type of Rotor Construction:

• Segmental rotor

• Radially laminated rotor

• Axially laminated rotor

Construction



Obtained by scooping out iron material in the quadrature axis

Construction





Axially Laminated Rotor:

• Flux barriers are introduced in the quadrature flux path

• Flux barriers are made of thin sheets of non-magnetic material

• Brass or aluminimum is used as flux barriers

• Direct axis inductance is not affected much by flux barriers as their

thickness is very small

Radially Laminated Rotor:

• Compared to axially laminated rotor they are cheaper & easier

• Since circular laminations can be used

• Motor has self starting capability

Construction



Other Types of Radially Laminated Rotor:



Working Principle

• Balanced 3-phase sinusoidal supply voltage is given in the stator

• Produces a rotating magnetic field in the air gap which rotates at

synchronous speed

• Rotor accelerates towards synchronous speed with the help of

damper winding or cage winding provided

• Rotating magnetic field exerts reluctance torque on the rotor to align its

projecting poles or d-axis to have a minimum reluctance torque

• SyncREL starts as an induction motor and at running condition reluctance

torque pulls the rotor in synchronism with stator field



• 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.

Working Principle



Working Principle



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



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°.



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



Applications

• Pumps

• Conveyors

• Synthetic fiber manufacturing industries

• Textile industries

• For positioning control rods in nuclear reactors



Permanent magnet assisted SynRM (or)

Hybrid Synchronous reluctance motor

• When PMs are inserted into the rotor flux

barriers of a synchronous reluctance

motor, it becomes a permanent magnet

assisted synchronous reluctance motor

• The amount of PM flux is quite lower than the amount of rated flux

Features:

• Has Combined reluctance and magnetic alignment torque

• High inductance

• High field weakening capability

• Under excited operation for most of the load condition www.vidyarthiplus.com


Hybrid Synchronous reluctance motor

Radially magnetized Circumferentially magnetized



Radially magnetized:

• Magnet area is smaller than pole area at the rotor surface

• Has considerable reluctance torque & field weakening capability

Reason:

Permeance to q-axis flux is high

Axially magnetized:

• Magnet area is exceeds the pole area at the rotor surface

• Has less reluctance torque & limited field weakening capability

Reason:

Permeance to q-axis flux is very low



Controller for SyncREL





Documents

Unit-I Synchronous Reluctance Motor (SyncREL)