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Brushless DC Motor

July 12, 2020

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

Brushless DC motor is also known as electronically commutated motor or synchronous DC motor powered by DC electricity and produces AC electric current.

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

Construction of brushless Dc motor

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

  • The stator

The stator of this motor 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 rotor of the brushless motor 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.
  • And 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 is switched on, these electromagnets create a magnetic field in the armature which helps in rotating 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 performs 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 and this makes it validly used.

Brushless DC outer rotor motor

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

This motor operates only at a lower-rated current and has a low clogging torque so it’s not usually used.

Advantages of BLDC motor

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

  •  The velocity can be determined by frequency 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 the 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.
  • In addition, It doesn’t require airflow for inside cooling.

Disadvantages of the brushless motor

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

  • 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.