Brushless DC Motor

[attachment=17857]
Features of BLDC motor

Stator is Induction wound.
• Rotor in BLDC is permanent magnet instead of bulky winding in DC motor.
• Mechanical commutation in DC motor is replaced by Electronic commutation.
• Due to its low weight rotor, it has good dynamic Characteristics.
• Rotor position is sensed using “Hall sensors” .
• It has high starting cost but low running cost due to its low maintenance requirement.

Basic working principle illustrated

The brushless motor system consists of a wound stator, a permanent magnet rotor, a rotor position sensor, and a solid state switching assembly.

On the Brushless DC motors, the commutation is controlled electronically. For rotation to be achieved, the stator windings have to be energized in a sequence. The most common type of Brushless DC motors includes 3 stator windings.

The decision of which winding is to be energized relies heavily on knowing the rotor position (determined by the use of Hall effect sensors in the stator). The majority of DC Brushless motors have three Hall sensors on the non-driving end of the motor, and may be at 60° or 120° phase shift from one another.


Advantages


Summary of some of the major advantages of Brushless DC
motors

They offer high efficiency
Better performance at high speeds
Medium construction complexity, multiple fields, delicate magnets
High reliability (no brush wear), even at very high achievable speeds
Lower audible noise
High torque to inertia ratio
Sensorless speed control possible

Limitations

The first and most important limitation comes from the higher cost associated with Brushless DC motors, due to the high-power electronic devices used in the fabrication of the electronic speed controller.

The cost also substantially increases due to the manufacturing techniques employed in the construction of Brushless DC motor, since most designs require manual-labor, to hand-wind the stator coils. (brushed motors use armature coils which can be machine-wound).

Another limitation is related to torque ripple, which requires the motor to be controlled with advanced techniques (i.e. a more complex controller).