The Permanent magnet synchronous
motor is classified as below
Permanent magnet
synchronous motor (BLAC)(Sinusoidal waveforms)
PM Brushless DC motor ( BLDC
)( Trapezoidal waveforms )
Which are the main
parts of the BLDC motor?
Stator
It consists of winding similar to DC motor armature.
Rotor
It is made of permanent
magnet.
Hall sensors
They are embedded in the
stator on the non – driving end of the motor to sense the position of the
rotor. When the rotor magnetic pole pass near the hall sensors, they give high
or low signal indicates that the N or S pole passes near the sensors.
Give the reason behind
the name of ‘BLDC’motor.
The BLDC motor has
straight line speed torque characteristics similar to that of permanent magnet
direct current motor so it is called as BLDC motor.
Compare the sinusoidal
winding and trapezoidal winding in the BLDC motor.
Sinusoidal and
trapezoidal winding
The torque output of the
sinusoidal winding is smoother than the trapezoidal winding. The sinusoidal
winding requires extra winding interconnection which increases the weight and
cost of copper stator winding.
Give the examples of
rare earth alloys
Rare
earth alloy magnet
Samarium cobalt
Neodymium
Alloy of neodymium,
ferrite and boron
Compare rare earth
alloy magnet and ferrite magnet.
Ferrite
magnet
Low flux density per unit
volume
Less costly
Rare
earth alloy magnet
High flux density per
unit volume
Costly
High torque as compare to
ferrite magnet for same size
Improved size to weight
ratio
State the
configuration of the BLDC motor.
According of construction
of BLDC motor, it is configured as
Outer rotor motor
Inner rotor motor
Special configuration
motor
Compare outer rotor and inner rotor BLDC motor.
Outer rotor BLDC motor
High rotor inertia is necessary
The outer rotor motor has
much more magnetic material than the inner rotor motor
Application : computer disk, drives, cooling fans
Inner rotor BLDC motor
Lower inertia because of
small rotor diameter
Accelerate more rapidly
due to small rotor diameter
Most of the inner rotor
BLDC motor has multiple phase in order to reduce starting problems
Is there cogging problem in the slotless brushless inner rotor
BLDC motor?
Cogging
Problem
The stator of the inner
rotor BLDC motor has no teeth therefore there is no variation of permeance as
the rotor moves resulting no cogging problem.
How the sensing of the
rotor position is done in the stepper motor?
Stepper
Motor – Rotor Position
The rotor position of the
stepper motor is sensed by placing three sensors in the stator on the non –
driving end.
Whenever the rotor magnetic poles pass near the hall sensors, they produce either LOW or HIGH signal which indicates either N or S pole passing near the hall sensors.
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