DC Motor – BLDC Motor
The rotor winding must be eliminated from the DC motor in order to make it brushless motor. This can be done by turning the DC motor inside out, it means that the winding placed on the stator and permanent magnet on the rotor. The current reversal in the BLDC motor is automatically possible by using electronic switch instead of commutator and brushes.
Whether the BLDC motor
is operated on DC supply or AC supply?
BLDC Motor
The BLDC motor cannot be
driven directly by the direct current.
The current in the
external circuit must be reversed at certain rotor position. Therefore the BLDC
motor is actually driven by the three phase bridge inverter or AC supply.
Give reason : The
number of phases in the BLDC motor is limited.
Number of Phases
The BLDC motor is
available in the single phase, two phase and three phase configurations. There
are large numbers of coils distributed around the stator but each coil requires
its own drive circuit. Therefore, the number of phases in the BLDC motor is
limited.
State the condition of
maximum torque in the BLDC motor. How is it possible?
BLDC Motor – Maximum
Torque
( 1 ) The torque in the BLDC
motor becomes maximum when the stator and rotor magnetic field is 900
with respect to each other.
( 2 ) As the stator winding
consists of three phase winding, the stator magnetic field advances only by 600.
( 3 ) The stator magnetic field
must be 900 ahead of rotor magnetic field in order to generate
constant torque.
( 4 ) It is not possible to
maintain 900 torque angle but it is possible an average of 900
torque angle by working between stator magnetic field 600 and 1200.
State the advantages
of Permanent magnet synchronous motor.
Advantages
No brushes or slip –
rings
No sparking
No brush maintenance
How many phases are
energized during commutation in the three phase BLDC motor?
Commutation Sequence
Each commutation sequence
has one winding is energized to positive, the other is energized to negative
and third is in non – energized or floating.
State the advantages
of BLDC motor over DC motor and Induction motor.
Advantages of BLDC motor
Fast dynamic response
High efficiency
Quiet operations
High speed range
Better torque – speed
characteristics
State the applications of the BLDC motor.
Applications of BLDC motor
Constant load : Fan, Blower, Pump
Variable load : Compressors,
Dryers, Washers, Fuel pump control, Electronic steering control, Robotic arm
control, Gyroscope control
Positioning control : Torque
control loop, Position loop control, Computer numeric control machine, Process
control, Conveyor control
Give reason : The PMBLDC motor is called as Electronic
commutated motor.
Electronic Commutated Motor
There is no mechanical commutator in the PMBLDC motor.
Therefore the function of
current reversal is done by semiconductor switches with rotor position sensor.
The semiconductor switch may be IGBT or MOSFET. Therefore, the PMBLDC motor is called as electronic commutated motor.
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