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Brush-less DC Motor: What Is It? How Does It Work? Advantages,Disadvantages & Uses

A motor turns electrical energy into mechanical energy when it is provided. Different types of motors are commonly used. Brushless DC motors (BLDC) are a type of motor that has a high efficiency and outstanding controllability and is extensively utilized in a variety of applications.

In comparison to other motor types, the BLDC motor saves energy. Brushless DC motors, as their name suggests, do not utilize brushes. Brushed motors use brushes to carry current from the commutator to the rotor’s coils. So, how does a brushless motor provide electricity to the rotor coils?This blog discusses what a Brushless DC Motor is? How does it operates? Its advantages, limitations, and applications.

What is a BLDC Motor?

Brushless DC electric motors also known as electronically commutated motors (ECMs, EC motors). A Brushless DC Motor is similar to a Brushed DC Motor but as the name suggests, a BLDC doesn’t use brushes for commutation but rather they are electronically commutated.  Brushes are utilized to deliver power to the rotor in traditional Brushed DC Motors as they turn in a fixed magnetic field.

The rotor of a brushless DC motor is made up of permanent magnets, and the stator is made up of polyphase armature windings. It differs from the conventional dc motor in such that it doesn’t contain brushes and the commutation is done electrically, using an electronic drive to feed the stator windings. These types of motors are highly efficient in producing a large amount of torque over a vast speed range.These motors are highly effective at providing a lot of torque across a wide speed range. They’re known for their quiet operation and the ability to hold torque when stationary.

Construction of BLDC Motor

The replacement of the mechanical commutator with an electronic switch circuit is the primary design difference between brushed and brushless motors. Keeping that in mind, a BLDC Motor is a type of synchronous motor in the sense that the magnetic field generated by the stator and the rotor revolve at the same frequency.Brushless motors are available in single phase, two phase, and three phase variants. The three-phase BLDC is the most common of these.

The following image shows the cross-section of a BLDC Motor.

BLDC Cross Section

As you can see in the image, a BLDC Motor consists of two main parts: a stator and a rotor.

  • Stator

The stator of a BLDC motor has a similar construction to that of an induction motor. It is constructed of layered steel laminations with axially cut winding grooves. The winding of a BLDC motor differs slightly from that of a standard induction motor.

BLDC Motor Stator

Most BLDC motors are made up of three stator windings coupled in a star or ‘Y’ pattern (without a neutral point). The stator windings are also categorized into Trapezoidal and Sinusoidal Motors based on the coil interconnections.

BLDC Motor Back EMF

Both the drive current and the back EMF in a trapezoidal motor are in the shape of a trapezoid (sinusoidal shape in case of sinusoidal motors). In automotive and robotics, 48 V (or less) rated motors are commonly utilized (hybrid cars and robotic arms).

  • Rotor

The rotor part of the BLDC Motor is made up of permanent magnets (usually, rare earth alloy magnets like Neodymium (Nd), Samarium Cobalt (SmCo) and alloy of Neodymium, Ferrite and Boron (NdFeB)).

The number of poles can range from two to eight, with North (N) and South (S) poles alternately positioned depending on the application. Three possible layouts of the poles are shown in the image below. The magnets are situated on the rotor’s outside circumference in the first scenario.

BLDC Motor Rotor

The magnetic-embedded rotor is the second variant, in which rectangular permanent magnets are integrated into the rotor’s core. The magnets are put into the rotor’s iron core in the third case.

  • Position Sensors (Hall Sensors)

Since a BLDC motor has no brushes, the commutation is controlled electronically. The stator windings must be energized in a specific order in order to rotate the motor, and the location of the rotor (i.e. the North and South poles of the rotor) must be known in order to precisely energize a specific set of stator windings.

The position of the rotor is normally detected and converted into an electrical signal using a Position Sensor, which is usually a Hall Sensor (that works on the concept of Hall Effect). To sense the rotor’s position, most BLDC Motors use three Hall Sensors integrated in the stator.

The output of the Hall Sensor will be either HIGH or LOW depending on whether the North or South pole of the rotor passes near it. By combining the results from the three sensors, the exact sequence of energizing can be determined.

Construction Methods:

A BLDC motor can be built in one of two ways: with the rotor outside the core and the windings within the core, or with the windings outside the core. The rotor magnets act as an insulator in the first arrangement, reducing the rate of heat dissipation from the motor and allowing it to run at low current. It’s commonly found in fans. The motor dissipates more heat in the latter configuration, resulting in an increase in torque. It’s a component of hard disk drives.

  • Inner Rotor Design

Rotor magnets do not insulate heat inside the rotor because it is positioned in the core, hence heat is easily dissipated. As a result, inner rotor designed motors create a lot of torque and are widely employed.

  • Outer Rotor Design

The rotor surrounds the winding, which is located in the motor’s core, in an outer rotor design. The heat from the motor is trapped inside the rotor by the magnets, which prevent it from dissipating. This type of motor has a low cogging torque and runs at a lower rated current.

Working Principle and Operation of BLDC Motor

BLDC motor works on the principle similar to that of a conventional DC motor, i.e., the Lorentz force law which states that whenever a current carrying conductor placed in a magnetic field it experiences a force.  The magnet will experience an equal and opposite force as a result of the reaction force. The current carrying wire is stationary in a BLDC motor while the permanent magnet moves.

When a supply source electrically switches the stator coils, it transforms into an electromagnet and begins to produce a consistent field in the air gap. Despite the fact that the source of power is DC, switching produces an AC voltage waveform with a trapezoidal shape. The rotor continues to rotate due to the force of interaction between the electromagnet stator and the permanent magnet rotor.

Advantages of a BLDC Motor:

  • Better speed versus torque characteristics
  • Less overall maintenance due to absence of brushes
  • Reduced size with far superior thermal characteristics
  • Higher speed range and lower electric noise generation.
  • It has no mechanical commutator and associated problems
  • High efficiency and high output power to size ratio due to the use of permanent magnet rotor
  • High speed of operation even in loaded and unloaded conditions due to the absence of brushes that limits the speed
  • Smaller motor geometry and lighter in weight than both brushed type DC and induction AC motors.
  • Long life as no inspection and maintenance is required for commutator system
  • Higher dynamic response due to low inertia and carrying windings in the stator
  • Less electromagnetic interference
  • Low noise due to absence of brushes

Disadvantages of Brushless Motor

  • These motors are costly
  • Electronic controller required control this motor is expensive
  • Not much availability of many integrated electronic control solutions, especially for tiny BLDC motors
  • Requires complex drive circuitry
  • Need of additional sensors

Applications of Brushless DC motor 

Brushless DC motors (BLDC) are used for a wide range of applications in the areas of industrial control, automotive, aviation, automation systems, health care equipments, and so on, including variable loads, constant loads, and positioning.

  • Computer hard drives and DVD/CD players
  • Electric vehicles, hybrid vehicles, and electric bicycles
  • Industrial robots, CNC machine tools, and simple belt driven systems
  • Washing machines, compressors and dryers
  • Fans, pumps and blowers.

Hope this blog helps you to understand about the brushless dc motor working principle and applications. We ,MATHA ELECTRONICS  will come back with more informative blogs.

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