Brushless Dc Motor

Brushless DC Motor Working Principle and Applications

What is Brushless DC motor?

Brushless DC electric motors also known as electronically commutated motors (ECMs, EC motors). 

Primary efficiency is a most importent feature for BLDC motors. Because the rotor is the sole bearer of the magnets and it doesn’t require any power. i.e. no connections, no commutator and no brushes. In place of these, the motor employs control circuitry. To detect where the rotor is at certain times, BLDC motors employ along with controllers, rotary encoders or a Hall sensor.

Construction of Brushless DC motor

In this motor, the permanent magnets attach to the rotor. The current-carrying conductors or armature windings are located on the stator. They use electrical commutation to convert electrical energy into mechanical energy. 

The main design difference between a brushed and brushless motors is the replacement of mechanical commutator with an electric switch circuit.  A BLDC Motor is a type of synchronous motor in the sense that the magnetic field generated by the stator and the rotor revolve at the same frequency.

Brushless motor does not have any current carrying commutators. The field inside a brushless motor is switched through an amplifier which is triggered by the commutating device like an optical encoder.

The layout of a DC brushless motor can vary depending on whether it is in “Out runner” style or “Inrunner” style.

  • Outrunner – The field magnet is a drum rotor which rotates around the stator. This style is preferred for applications that require high torque and where high rpm isn’t a requirement.
  • In runner – The stator is a fixed drum in which the field magnet rotates. This motor is known for producing less torque than the out runner style, but is capable of spinning at very high rpm.

Working Principle of Brushless DC motor

BLDC motor works on the principle similar to that of a Brushed DC motor. The Lorentz force law which states that whenever a current carrying conductor placed in a magnetic field it experiences a force. As a consequence of reaction force, the magnet will experience an equal and opposite force. In the BLDC motor, the current carrying conductor is stationary  and the permanent magnet is moving.

When the stator coils get a supply from source, it becomes electromagnet and starts producing the uniform field in the air gap. Though the source of supply is DC, switching makes to generate an AC voltage waveform with trapezoidal shape. Due to the force of interaction between electromagnet stator and permanent magnet rotor, the rotor continues to rotate.

With the switching of windings as High and Low signals, corresponding winding energized as North and South poles. The permanent magnet rotor with North and South poles align with stator poles which causes the motor to rotate.

Advantages of Brushless DC motor

  • Less overall maintenance due to absence of brushes
  • Reduced size with far superior thermal characteristics
  • Higher speed range and lower electric noise generation.
  • It has no mechanical commutator and associated problems
  • High efficiency and high output power to size ratio due to the use of permanent magnet rotor
  • High speed of operation even in loaded and unloaded conditions due to the absence of brushes that limits the speed
  • Smaller motor geometry and lighter in weight than both brushed type DC and induction AC motors.
  • Long life as no inspection and maintenance is required for commutator system
  • Higher dynamic response due to low inertia and carrying windings in the stator
  • Less electromagnetic interference
  • Low noise due to absence of brushes

Limitations of Brushless DC motor

  • These motors are costly
  • Electronic controller required control this motor is expensive
  • Requires complex drive circuitry
  • Need of additional sensors

Applications of Brushless DC motor 

Brushless DC motors (BLDC) use for a wide variety of application requirements such as varying loads, constant loads and positioning applications in the fields of industrial control, automotive, aviation, automation systems, health care equipments etc. 

  • Computer hard drives and DVD/CD players
  • Electric vehicles, hybrid vehicles, and electric bicycles
  • Industrial robots, CNC machine tools, and simple belt driven systems
  • Washing machines, compressors and dryers
  • Fans, pumps and blowers.