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Brushless DC Motors
Group Members
Malik Muhammad Kamal
(Basics of DC Motor)
Haris Zaman
(Construction of BLDCMs)
Haseeb Akhtar
(Controller Circuit)
Malik Muhammad Moin
Motor Basics
BLDCMs Introduction
• 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
• BLDCMs are generated by virtually
inverting the stator and rotor of PM DC motors.
• The stator consists of several coils which current is
led through Creating a magnetic field that makes
the rotor turns
Introduction Cont…
• Basically BLDCMs are equivalent to the Permenant Megnet AC Motors
except one difference The Haul Sensor.
• The brushless motor, unlike the DC brushed motor, has the
permanent magnets glued on the rotor.
• It has usually 4 magnets around the perimeter. The stator of the
motor is composed by the electromagnets, usually 4 of them,
placed in a cross pattern with 90o angle between them.
• The major advantage of the brushless motors is that, due to the
fact that the rotor carries only the permanent magnets, it needs
of NO power at all. No connection needs to be done with the
rotor, thus, no brush-commutator pair needs to be made! This is
how the brushless motors took their name from.
Construction Cont…
• 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
• As there is no Brushes and hence no commutators ,the current direction of
the conductor on the stator controlled electronically.
• Hall sensor used to determine the position during commutation
• These Sensors sens the position of the coil acuratly and hence direction
of current remain in one side due to control circuit.
The Haul Sensor
Haul Effect
• When a magnetic field applied to a system with electric current a hall voltage
Perpendicular to the field and to current is generated
•Halls Sensors sense the position of
the coils
• The Decoder Circuit turns
appropriate switches on and off
• The voltage through the specific
coils turns the motor
Applications of
Speed Torque Characteristics
General Applications
• Single-speed – For single-speed applications, induction motors are more suitable,
but if the speed has to be maintained with the variation in load, then because of the
flat speed-torque curve of BLDC motor, BLDC motors are a good fit for such
Adjustable speed – BLDC motors become a more suitable fit for such applications
because variable speed induction motors will also need an additional controller, thus
adding to system cost. Brushed DC motors will also be a more expensive solution
because of regular maintenance.
Applications Cont…
• Position control – Precise control is not required applications like an induction
cooker and because of low maintenance; BLDC motors are a winner here too.
However, for such applications, BLDC motors use optical encoders, and complex
controllers are required to monitor torque, speed, and position.
Low-noise applications – Brushed DC motors are known for generating more
EMI noise, so BLDC is a better fit but controlling requirements for BLDC motors
also generate EMI and audible noise. This can, however, be addressed using FieldOriented Control (FOC) sinusoidal BLDC motor control.
Industrial Applications
• Consumer:
Hard Drives, CD/DVD Drives, PC Cooling Fans, toys, RC
airplanes, air conditioners
• Medical:
Artificial heart, Microscopes, centrifuges, Arthroscopic
surgical tools, Dental surgical tools and Organ transport pump system.
• Vehicles:
electronic power steering, personal electric vehicles
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