I. By Rajeev

Kumar

Permanent Magnent Synchronous Macnine

Permanent Magnet Technology

The use of permanent magnets (PMs) in construction of electrical machines

brings the following benefits:

No electrical energy is absorbed by the field excitation system and thus there are no excitation losses which means substantial increase in the efficiency,

Higher torque and/or output power per volume than when using electromagnetic excitation,

Better dynamic performance than motors with electromagnetic excitation (higher magnetic flux density in the air gap),

Simplification of construction and maintenance,

Reduction of prices for some types of machines.

Permanent Magnet Classification

Permanent Magnet

Permanent Magnet Synchronous

Machine (PMSG)

Permanent Magnet Brushless Machine

(BLDC)

Permanent Magnet Classification

Introduction

PM Synchronous Machine are widely used in

Wind mile generation

Industrial servo-applications due to its high-performance characteristics.

General characteristics

Compact

High efficiency (no excitation current)

Smooth torque

Low acoustic noise

Fast dynamic response (both torque and speed)

Expensive

Construction

PMSM

Stator Rotor

Inner Rotor & Outer Rotor

Longitudinal & Transversal

Radial Flux & Axial Flux

Radial & Axial Rotor

If the normal vector is perpendicular to

axis, machine is called Radial. If the

normal vector is parallel with the axis, the

machine is called Axial.

Radial Rotor

Higher power rating achieved by

increasing the length of machine.

Used in

Ship propulsion

Robotics

Traction

Wind systems

Radial & Axial Rotor

Axial Rotor

Smaller than Radial machine

High torque density

Used in

Gearless elevator systems

Rarely used in Traction

Generation

Longitudinal & Transversal Rotor

In transversal flux machines, the

plane of flux path is perpendicular to

the direction of rotor motion.

Transversal flux machines can be

adjusted independently current

loading and the magnetic loading.

Used in

Applications with high torque

density requirement.

Free piston generators for hybrid

vehicles.

Ship propulsion and wind system.

Inner and Outer Rotor

Inner Rotor

The interior-magnet rotor has radially

magnetized and alternately poled magnets.

Because the magnet pole area is smaller

than the pole area at the rotor surface, the

air gap flux density on open circuit is less

than the flux density in the magnet.

The magnet is very well protected against

centrifugal forces. Such a design is

recommended for high frequency high

speed motors.

Outer Rotor

The surface magnet motor can have

magnets magnetized radially or sometimes

circumferentially. An external high

conductivity non-ferromagnetic cylinder is

sometimes used. It protects the PMs against

the demagnetizing action of armature

reaction and centrifugal forces, provides an

asynchronous starting torque, and acts as a

damper.

The magnet is very well protected against

centrifugal forces. Such a design is

recommended for high frequency high

speed motors.

PM Configuration

PM (Permanent

Magnet )

Surface Magnet

Inset Magnet

Buried Magnet

Surface and Buried Magnet

Surface Magnets Simple construction

Small armature reaction flux

Permanent magnets not

protected against armature fields

Eddy-current losses in

permanent magnets

Expensive damper

Buried Magnets Relatively complicated

construction

High armature reaction flux

Permanent magnets protected

against armature fields

No eddy-current losses in

permanent magnets

Less expensive damper

Permanent magnet B-H curve

Operating Principle

In the permanent magnet synchronous

generator, the magnetic field is obtained by

using a permanent magnet, but not an

electromagnet. The field flux remains

constant in this case and the supply required

to excite the field winding is not necessary

and slip rings are not required.

All the other things remain the same as

normal synchronous generator.

The EMF generated by a synchronous

generator is given as follows

Equivalent Circuit – rotor side

Voltage Equation of PM machine in rotor reference

Equivalent Circuit – rotor side

Fig: PM equivalent for d-axis & q-axis

Equivalent Circuit – rotor side

Flux Linkage equations

The Flux Linkage can be generated field current

Vector Diagram

Stator reference axis X-Y axis

Rotor reference axis d-q axis

Thank You

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