Brushless Dc motor
Brushless Dc motor or BLDC motor is a special type of motors as it doesn’t contain brushes, and it has high efficiency typically around 85-90% in producing large amounts of torque over a vast speed range, brushless Dc motor 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 brushless motor has the same construction of Ac induction motor and brushed Dc motor; like all other motors, there is a stator and a rotor.
The stator of this motor made of laminated steel stacked up to carry the windings which may be arranged in star (Y) or delta (∆) pattern.
In star pattern:
we have high torque at low RPM.
and in delta pattern:
we have low torque at low RPM.
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.
As this motor has 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 we have permanent magnets on the outside and also a spinning armature contains electromagnets, and when we switched on the power these electromagnets create a magnetic field in the armature which helps in rotating the armature, and to keep the rotation of the armature the brushes change the polarity of the pole.
That’s the small differences and after that, we can say that BLDC motor has the basic principles of the brushed Dc motor; there is a rotor which is the rotating part contains rotor magnets and the stator which is the stationary part contains stator windings.
The permanent magnets are attached to the rotor and move the electromagnets to the stator, and we use a high power transistor to active 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 as:
Brushless Dc Inner rotor motor:
In inner rotor motor, we locate the rotor in the center of the motor and the stator winding surround the rotor, and the rotor magnets don’t insulate heat inside and heat gets dissipated easily because we locate the rotor 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 outer rotor motor, the winding is located in the core and surrounded by the rotor, and the magnets trap the heat of the motor inside and don’t allow 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:
- We can determine the velocity by frequency so, It’s more efficient which depends on the current, not the voltage.
- We have less mechanical energy loss while the friction is less and that enhance the efficiency.
- It can operate at high-speed under any condition.
- There is no spark so we have less noise during operation.
- We can easily accelerate and decelerate the motor while it has low rotor inertia.
- It provides large torque over a vast speed range, so, makes it a high-performance motor.
- It’s more reliable, so, high life expectancies, and maintenance-free operation.
- In addition, It doesn’t require air flow for inside cooling.
Disadvantages of brushless motor:
Unfortunately, we could find some disadvantages on any motor so:
- BLDC motor cost is higher than in a brushed motor.
- Insulation of winding may get damaged as heat weakens the magnets because we can supply limited high power to the motor.
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