This presentation describes one of the special electrical machines

1. SPECIAL ELECTRICAL MACHINES
1
PERMANENT MAGNET BRUSHLESS
DC MOTORS

2. PERMANENT MAGNET BRUSHLESS
DC MOTORS
• It is a brushless dc motor.
• It has a PM rotor type.
• Why we are choosing PMBLDC Motor…..
• Comparison between conventional dc motor
& PMBLDC Motor.
2

3. FEATURES CONVENTIONAL DC
MOTOR
PMBLDC MOTOR
Maintenance High low
Commutation method Mechanical contact
between brushes &
commutator.
Electronic switching using
power semiconductor
devices ie,
transistor,MOSFET
Detecting method Automatically detected by
brushes
Rotor position can be
detected by using sensor
ie, Hall sensor, optical
sensor
controllable Speed controllable is
difficult
Speed can be easily
controllable, so that it is
possible to have very high
speed

4. Conventional dc motor

5. PMBLDC MOTOR

6. Construction of PMBLDC motor
• It consist of two parts mainly stator & rotor.
• Stator is made up of silicon steel stampings
with slots.
• The slots are accomodated armature
windings.
• This winding is wound with specified no.of
poles.(even number).
• This winding connected a dc supply through a
power electronic switching circuits.

7. • Rotor accomodates PM.
• The rotor shaft carries a rotor position sensor.
• Sensor provides information about the
position of the shaft.
• This shaft position signal send to electronic
commutator.

8. advantages
• There is no mechanical commutator, so that
size become very small.
• Speed can be easily controlled.
• Regenerative braking is possible.

9. applications
• Automotive application.
• Textile and industries.
• Computer and robotics.
• Small appliances such as fans, mixers etc

10. Commutation in DC motors
(1) Mechanical commutator.
(2) Electronic commutator.
• Construction of Mechanical commutator
• Commutator is made up of specially designed
commutator segments,made of copper.
• These segments are insulated from each
other by a thin layer of mica.
• It forms a cylindrical shape.

11. Mechanical commutator

12. • It consist of 2 pole machine with 12
commutator segments.
• Carbon brush A contacts with CS 1 and brush
B contacts with CS 7.
• When a dc supply is connected across A & B,
a dc current passes through A-CS1-tapping1-
tapping 7-CS 7 and through B.
• The current has 2 parallel path in the
armature winding.
• Parallel path 1= 1-2-3-4-5-6-7
• Parallel path 2=1-12-11-10-9-8-7

13. • The current crossing through the armature
conductor setup an mmf along the axis A and B
• The commutator rotates along the clockwise
direction, now the brush A makes contact with
CS2 and brush B with CS 8.
• Now there are two parallel path 1 is 2-8 &
parallel path 2 is 2-1-12-11-10-9-8.
• Function of commutator and bush arrangement is
to setup an armature mmf whose axis is always in
quadrature with the main field mmf irrespective
of the speed of rotation of the motor.

14. Electronic commutator

15. Switching circuit of electronic
commutator

16. Step 1: S1 & S1’ are closed.other switches are
open
• current has 2 parallel path in armature winding.
• Parallel path 1 =1-2-3-4-5-6-7
• Parallel path 2 =1-12-11-10-9-8-7
• These current setup in the armature mmf.
Step 2: S1 & S1’ are opened,S2 & S2’ are closed
• Now the current passes through tapping 2-8.
• Thus operating switches in the sequential
manner, we are getting a revolving magnetic
field.

17. • For normal electronic commutator , 6 switching
devices are employed.
• Here the windings may be connected either star
or delta connection.
• Therefore the winding should have 3 tappings.
• Figure draw ..

18. Comparison between mechanical and
electronic commutator
Mechanical commutator Electronic commutator
Commutator is made up of commutator
segments and mica insulation. brushes
are made up of carbon.
Power electronics switching devices are
used in the commutator.
Shaft position sensing is inherent in the
arrangements.
It requires a separate rotor position
sensor.
Commutator arrangement is located in
the rotor
Commutator arrangement is located in
the stator.
Sliding contact between commutator and
brushes.
No sliding contacts.

19. Sparking takes place. There is no sparking.
It requires a regular maintenance. It requires less maintenance.
Number of commutator segments are
very high.
Number of switching devices is limited to
6.
Difficult to control the voltage available
across tapping
Voltage available across armature
tappings can be controlled by PWM
techniques.
Highly reliable Reliability depends on the switching
devices.

20. OPERATION OF PMBLDC MOTOR
• When dc supply is given to the motor,the
armature winding draws a current.
• The current distribution with in the stator
armature winding depends upon the rotor
position.
• The mmf perpendicular to the permanent
magnet field is setup.
• Then the armature conductor experience a
force.
• The force develops a torque in the rotor.

21. • If this torque is more than the opposing
frictional and load torque, the motor starts.
• It is self starting motor.

25. Hall sensor

27. Hall effect

32. Optical sensor
grating
light emitter
light sensor
decode circuitry