In this article we will talks about a DC motor. Which is the ideal choice for many applications. We can use BLDC motors where needed for reliability, low maintenance, low noise, speed control and low power consumption. Specifically, we are going to learn how a brushless DC motor works. We can assume already by its name that this type of electric motor has no brushes.
What is BLDC Motors
The brushes are sliding devices which allow the electricity to
flow into the copper coil of the motor. The brushless motors have no sliding
elements on the DC collector.
Brushless motors are available with either an inner rotor or
an outer rotor as shown below. The motor that rotates outwards is called the
"outrunner" motor. The BLDC Ceiling Fan is an example of an outrunner
DC motor. The number of windings used in a brushless motor is called the number
of stages. Although brushless motors can be manufactured in several stages,
three-phase brushless motors are the most common.
So, this completely solves the problem of maintenance and
replacement of brushes and other electrical contacts. Typical DC motors use
brushes for their operation, producing sparks or friction noises. But brushless
motors do not produce sparks or friction noises. Brushless motors have a very
interesting feature which makes them eco-friendly.
Why want use BLDC Motors
Where sparks are dangerous, for example in environments where
ignitable gases are present. Eg. UPS Battery room exhausts fan. This type of
motor has a rotor with permanent magnets. It cannot have spark since there are
no contacts on the rotor. Stator has electro magnets excited by winding and
coils this is an important difference compared to the traditional brushes DC
motor.
There will be a stator and rotor with electromagnets to
increase the magnetic fields. Therefore, such DC motors have a high mechanical
power density depending on the unit of load. The torque of the brushless motor
is due to the magnetic interaction imposed by the electro magnets.
Since the latter can have stator and rotor composed of electro
magnets to increase the magnetic fields. It has a high density of mechanical
power depending on the unit of load (Watts) of the motor. The torque of the
brushless motor is due to the magnetic interaction imposed by the electro
magnets.
Function of Brushless DC Motors
On the permanent magnets there is a precise sequence of
excitation of the electromagnets. It imposes on permanent magnets in angular
movement. It is always in the same direction and is as constant as possible in
the excitation. Its sequence is cyclic, the rotor continues its rotation until
it is repeated.
The sequence from time to time to be more specific the
sequence of excitation of the electro-magnets inside the stator is such that
the magnets of the rotor are attracted. The electromagnets without ever
reaching them as the excitation is always and only of those coils not reached
when electricity flows into coil. one the opposite poles of the rotor and
stator are attracted to each other when the rotor is getting close to the coil
one.
Brushless DC Motor Controller
A brushless three-phase motor to drive, each of the phases must be capable of operating at the input supply voltage or ground. To accomplish this, three "half bridge" drive circuits are used, each with two switches. The switches may be bipolar IGBTs, Transistors, or MOSFETs, depending on the current and voltage required.
Brushless DC Motors Rotation
As the rotor approaches the coil, electricity flows to the
coil and the rotor turns to the adjacent coil. Later rotor magnet reaches near
coil the electricity will flow again into coil. This process continuously going
on rotates the rotor.
but with opposite polarity this process is repeated
continuously inside the motor ensuring a constant rotation of the rotor. As the
rotor follows the magnetic flux, the magnetic field is generated in the correct
order in the coils of the stator. In the case of more coils always multiples of
two it makes sense to use a sequence. The sequence uses to increase the
magnetic flux to which the permanent magnets are subjected and turning off only
the opposite electromagnets.
What do BLDC Controller
This simple foresight increases the torque. That is the power
that the motor can supply without substantially modifying its design criteria
the greater the number of coils the smooth rotation of rotor. So, these will
have a constant torque.
But how to know the exact movement that excites the brushless dc motor (BLDC). The correct sequence of electromagnets which will allow continuity of
the rotary motion for this purpose an electronic controller is typically used.
This is done with the help of a sensor in the controller to
detect the exact position of the rotor magnets. So, the sensor will decide
which coil to activate according to the correct excitation sequence.
The modern brushless dc motor sensors can use to observe the
configuration of a standard DC brushless motor.
The protection diodes presence is necessary to protect the sensor from negative self-inductance in case we need to suddenly block the power supply from one of the coils. There are basically two families of brushless motors those with an external stator and those with an internal stator.
The Advantage of Brushless DC (BLDC) Motors
Brushless DC motors are providing low energy costs, more
durability, does not require any maintenance, it can also use in inflammable
gas areas. It is more expensive than traditional brush motors of the same
power.
However, the brushless motor has also its limitations, like
requires an electronic driver in order to control the right excitation sequence
uses. Brushless DC motors with permanent magnets will have a lower rated power
than conventional stator rotor motors with brushes.
Applications of Brushless DC Motors (BLDC)
Brushless DC motors (BLDC) that are used for a wide variety of application requirements such as constant load, varying load and positioning applications in the fields of industries. Eg. automotive, automation systems in industries and Hospital equipments, etc. Some applications here we mention use BLDC motors,
- Electric Bicycles, Electric Vehicles and Hybrid Vehicles
- Hospital auto beds, ECG machine, Cirinch pumps
- Computer hard drives
- Fans, Blowers and Pumps
- Robotics, CNC machine tools
- Simple belt driven systems
- AC compressors and dryers
Conclusion
we can summarize the main strength points of the brushless DC motor. brushless motor is noiseless, it is reliable and has a very low maintenance parameter.
There have a lot of things to be learned from the adoption of brushless motors in sector of automobiles. When the car is running things like pumps and fans have shifted to brushless motors from brushed motors for their increased reliability. Now a days by the end 2021, most of the comercial and industrial motors is that are use BLDC technology. The main advantage is very low rate of field failures and reduce maintenance requirements. But, we have to overcome the additional cost of the brushless motor and its electronics parts.
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