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Consider the following statements regarding Brushless DC motors and select the correct option. (i) In Brushless motors, there is a provision of permanent magnets that will rotate around a moving armature. (ii) The brush-commutator assembly of a conventional DC motor is replaced by an electronic controller in the Brushless DC motors. (iii) For same kW rating, the Brushless DC motor is less expensive than the Brushed conventional DC motor.
(i) and (ii) are false
(ii) and (iii) are false
Only (ii) is false
(i) and (iii) are false
(i) and (iii) are false
Statement (i) is false because in BLDC motors, permanent magnets are on the rotor and the armature windings are on the stationary stator. Statement (ii) is correct as electronic commutation replaces the mechanical brush-commutator. Statement (iii) is false because BLDC motors involve higher manufacturing costs due to high-energy permanent magnets and complex electronic controllers compared to conventional brushed DC motors.
IEC 60034-1
Statement (i) is false because in BLDC motors, permanent magnets are on the rotor and the armature windings are on the stationary stator. Statement (ii) is correct as electronic commutation replaces the mechanical brush-commutator. Statement (iii) is false because BLDC motors involve higher manufacturing costs due to high-energy permanent magnets and complex electronic controllers compared to conventional brushed DC motors.
TeтАЛ=ktтАЛтЛЕIaтАЛ тАФ Electromagnetic torque produced in the BLDC motor where ktтАЛ is the torque constant.
EbтАЛ=keтАЛтЛЕ╧Й тАФ Back EMF equation where keтАЛ is the back EMF constant and ╧Й is angular velocity.
The BLDC motor functions based on the electronic commutation principle. Hall effect sensors or back-EMF sensing techniques determine the rotor position, allowing the controller to energize stator phases in a specific sequence to produce a rotating magnetic field that exerts torque on the rotor magnets.
BLDC motors are externally excited by an electronic driver circuit.
The stator consists of a 3-phase winding and the rotor consists of permanent magnets.
Absence of brushes eliminates sparking, radio frequency interference, and mechanical wear.
Higher efficiency and power density.
Longer operational life due to lack of brush wear.
High speed operation capability.
Higher initial cost due to electronic controller.
Complex control system requirement.
Requires external commutation circuitry.
Electric Vehicles (EVs)
Industrial automation and robotics
Computer cooling fans and hard disk drives
In brushed motors, the armature is rotating (moving), whereas in BLDC motors, the armature is stationary (stator).
BLDC motors are generally more expensive for the same power rating due to the sophisticated semiconductor-based controller and rare-earth magnets required for high performance.
D is correct тАФ Statements (i) and (iii) are technically incorrect, while (ii) is a correct definition of a BLDC motor.
Remember that BLDC motors are essentially 'inverted' DC motors where the armature (stator) is fixed and the field (rotor) rotates, managed by solid-state switching.
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