The brushless direct current motors or as is often called BLDC motors are characterized by not using brushes. For brushed motors, the brushes are used to pass the current through the switch to the coils on the rotor; whereas, in brushless motors,
- The coils aren’t on the rotor, the rotor is just a permanent magnet;
- The coils aren’t rotating, but instead, they’re connected to the stator.
- Since the coils are not running, a brush and a switch are not necessary.
The other difference in the structure between a brushed and a brushless motor is that in brushed motor, the magnetic fields generated by the coils on the rotor are regulated by rotation, while the magnetic field generated by the stationary magnets is still constant. Therefore, in order to switch the speed of rotation, you set the voltage for the coils. In a BLDC, the rotation of the permanent magnet is achieved by changing the polarity of the magnetic fields generated around it by the stationary coils. Also, in order to regulate the rotation of the magnet, you can change the magnitude and direction of the current in these spools.
Advantages of BLDC
In order to better understand how a brushless DC engine operates, it is better to have a quick look at how a brushed motor works. In brushed motors, there are permanent magnets on the outside(stator) and a rotating armature in the inside containing an electromagnet. When the power is turned on, these electromagnets create a magnetic field in the armature and by repelling and attracting the magnets in the stator allow the armature to rotate. The brushes are used to change the polarity of the electromagnets to keep the spinning of the armature.
There are only two basic components in a brushless DC motor: the rotor and the stator. The rotor is the revolving element of rotor magnets, whereas the stator is a stationary component with windings of the stator. In the BLDC, the rotor is attached to permanent magnets and the electromagnets are transferred to the stator. High-power transistors are used to allow the shaft to be turned by electromagnets. The controller uses a solid-state circuit to conduct the power distribution.
In BLDC motors, with three coils on the stator, there are six electrical wires (two for each coil). The wirings are connected as displayed in the below image:
To control the rotation in a BLDC motor, the magnitude and direction of the current into these coils should be controlled. We continue by looking at the strengths of the BLDC engines below:
- Efficiency is a major advantage of BLDC motors because the total rotational force (torque) can be continuously controlled by them. On the other hand, the brushed motors achieve maximum torque only at a few rotational levels. Larger magnets would have to be used for a brushed motor to achieve the same torque as a brushless version. That’s why even tiny BLDC motors can generate considerable power.
The second major advantage is the controllability issue. Using feedback mechanisms, BLDC motors can be operated to deliver the desired torque and rotation speed precisely. This precision control, in effect,
- reduces the energy consumption and waste of power like heat generation,
- In situations where the motors are powered by a battery, it prolongs the battery life.
- Due to the lack of brushes, BLDC motors are highly reliable with low electrical noise generation. Whereas, for brushed motors, the brushes and commutator gradually wear down because of constant moving contact, and the creation of sparks at contact points. Electrical noise, in general, is a result of intense sparks that tend to occur in places where the brushes move through the gaps in the commutator. Therefore, BLDC motors are often considered preferred in applications where it is important to avoid electrical noise.
Brushless DC or BLDC motors continue to increase their popularity in industrial applications due to the numerous advantages they offer over their brushed DC motor equivalents. BLDC motor manufacturers typically build motors for electronics medical applications, computers, HVAC equipment, and automotive applications. In the industrial engineering industry, brushless DC motors are often used for automation and manufacturing engineering applications that improve overall efficiency and performance.
- Brushless motors are more effective because their velocity is dictated by the frequency at which the current is supplied, not by the voltage.
- In the absence of brushes, mechanical energy loss due to friction is smaller, which increases performance.
- The BLDC motor can work at high speed under any environment.
- There is no spark and much less noise during service.
- For more precise control, more electromagnets could be used on the stator.
- BLDC motors accelerate and decelerate quickly due to low rotor inertia.
- It is a high-performance engine that produces a strong torque per cubic inch over a wide range of speeds.
- BLDC engines do not have brushes that make them more efficient, with high life expectancy and maintenance-free service.
- No ionizing sparks are coming from the commutator, so electrical interference is also minimized.
- These conduction-cooled motors and no airflow are necessary for indoor cooling.