Brushless dc motor, Principles of Mechanical Vs Electronic Commentator Construction ,Hall sensors, Torque Speed Characteristics

1. Contents…
• Introduction & Comparison with DC and Induction Motor
• Motor basics
BLDC motor
• Principles of
• Mechanical Vs Electronic Commentator
• Construction
• Hall sensors
• Torque Speed Characteristics
• Dismantling of BLDC motor
• MOTOR PROTECTION
• Advantages
• Disadvantages
• Applications

2. Introduction…
• Although dc motors possess good control
characteristics and ruggedness, their performance
and applications are inhibited due to sparking and
commutation problems.
• The Permanent Magnet Brushless DC
(PMBLDC) motor is able to overcome the
limitations mentioned above and satisfy the
requirements of a variable speed drive.

4. • What is a motor
Converts electrical energy into kinetic energy
• How it works
Motor Basics

5. Brushless DC Motor(BLDC)
 Principles
• A BLDC is simply a normal dc motor turned inside
out, that means the coil is on the out side and the
magnets are inside
• The stator consists of several
coils which current is led through
Creating a magnetic field that
makes the rotor turns
• Unlike a brushed DC motor,
the commutation of a BLDC
motor is controlled
electronically.

6. Mechanicalcommutator Electroniccommutator
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.
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.

7. Construction
•Stator consists of stacked steel
laminations with windings placed in
the slots that are axially cut along the
inner periphery
•Rotor is made of permanent magnet and can vary from two to
eight pole pairs with alternate North (N) and South (S) poles.
Ferrite magnets and Rare earth alloy magnets are used in rotor

8. It is important to know the rotor position in order
to understand which winding will be energized
following the energizing sequence.
Rotor position is sensed by different ways some
of them are
1) Hall sensors
2) Optical encoders

9. Hall effect

10. Hall Sensors
When a magnetic field applied to a system with electric current a
hall voltage Perpendicular to the field and to current is generated.
This was discovered by Edwin Hall in 1879.

11. Torque-Speed Characteristic

12. DISASSEMBLED VIEW OF BRUSHLESS DC MOTOR

14. MOTOR PROTECTION
• Peak current :－This is the maximum instantaneous current
allowed to flow through the windings for safe operation. This
condition occurs in case of a short circuit.
• Under Voltage : – When the system is running on batteries, it
becomes important to cut off the supply if the battery voltage
drops below a particular limit.
• Hall Sensor Failure : – The commutation sequence will break,
which may cause the BLDC motor to become stuck and the
current to rise above a particular limit. Signal changes its logic
level or not. If it gets stuck to a particular level, then it can be
detected as a failure and the motor drive can be disconnected,
letting it run on inertia or be stopped by applying the brake.

15. Advantages
• Increased Reliability & Efficiency
• Longer Life
• Elimination of Sparks from Commutator
• Reduced Friction
• Faster Rate of Voltage & Current

16. Disadvantages
• Requires Complex Drive Circuitry
• Requires additional Sensors
• Higher Cost
•Some designs require manual labor
(Hand wound Stator Coils)

17. Applications
Consumer: Hard Drives, CD/DVD
Drives, PC Cooling Fans, toys, RC
airplanes, air conditioners

18. Medical: Artificial heart,
Microscopes, centrifuges,
Arthroscopic surgical tools, Dental
surgical tools and Organ transport
pump system.