Brushless DC Motor

July 12, 2020
brushless DC motor

Brushless DC motors or BLDC motors are special motors as they don’t contain brushes. Also, it has high efficiency, typically around 85-90%, producing large amounts of torque over a vast speed range.

Brushless DC motors are also known as electronically commutated motors or synchronous DC motors powered by DC electricity, and it produces AC electric current.

In brushless motors, the permanent magnets rotate around a fixed armature, which helps overcome the problem of connecting the current to the armature.

Construction of Brushless DC Motor

We can say that the brushless motor has the same construction as the AC induction motor and the brushed DC motor. Like all other motors, there is a stator and a rotor.

  • The Stator

This motor’s stator is made of laminated steel stacked up to carry the windings, which may be arranged in star (Y) or delta (∆) pattern.

Instar pattern:

We have high torque at low RPM.

And in delta pattern:

We have low torque at low RPM.

  • The Rotor

The brushless motor’s rotor made of permanent magnets and a variable number of poles depends upon the application requirements.

And the torque produced by the rotor depends upon the material of permanent magnet used as the higher the flux density of the material, the higher torque we get.

Applications of a Brushless Motor

As this motor has a high power to weight ratio, high speed, and electronic control, we use it in many applications as:

  • In computer peripherals (disk drives, printers)
  • Hand-held power tools
  • Vehicles ranging from aircraft to automobiles
  • For Small cooling fans
  • For gramophone records in direct-drive turntables

Working Principle of Brushless DC Motor

Before explaining the working principle, we should know that there are permanent magnets on the outside. Also, a spinning armature contains electromagnets. When the power switches on, these electromagnets create a magnetic field in the armature, which rotates the armature.

Additionally, to keep the rotation of the armature, the brushes change the polarity of the pole.

There is a rotor, which is the rotating part that contains rotor magnets and the stator, which is the stationary part that contains stator windings.

The permanent magnets are attached to the rotor and move the electromagnets to the stator. We use a high-power transistor to activate electromagnets for the shaft turns, and we use a solid-state to help the controller perform power distribution.

Types of BLDC Motor

We can usually find BLDC motor in two types; outer rotor and the inner rotor. The two types have the same working principles, but they differ in design.

Brushless DC Inner Rotor Motor

In the inner rotor motor, we locate the rotor at the center of the motor.  Also, the stator winding surrounds the rotor, and the rotor magnets do not insulate heat inside. The heat gets dissipated easily because the rotor is located in the core.

So we can get a large amount of torque from this type, which makes it validly used.

Brushless DC Outer Rotor Motor

In the outer rotor motor, the winding locates in the core and is surrounded by the rotor. The magnets trap the motor’s heat inside and do not allow it to dissipate from the motor.

We don’t usually use this motor, as it only at a lower-rated current and has a low clogging torque.

Advantages of the BLDC Motor

As this motor has no brushes, we can find many advantages as:

  • Frequency determines velocity, so; it’s more efficient as it depends on the current, not the voltage.
  • There is less mechanical energy loss while the friction is less, and that enhances efficiency.
  • It can operate at high-speed under any condition.
  • There is no spark, so there is less noise during operation.
  • They can easily accelerate and decelerate the motor while it has low rotor inertia.
  • It provides large torque over a vast speed range, so it makes it a high-performance motor.
  • It’s more reliable, with high life expectancies, and maintenance-free operation.
  • Also, It doesn’t require airflow for inside cooling.

Disadvantages of the Brushless Motor

Unfortunately, we can find some disadvantages for the motor as well.

  • The BLDC motor cost is higher than in a brushed motor.
  • Insulation of winding may get damaged as heat weakens the magnets because the supply of high power to the motor is limited.
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