Brushless DC Motors (BLDC Motor), Types, Uses, Comparison

Within the field of electrical engineering, Brushless DC Motors has become a game-changer due to its superior efficiency and performance. This article will examine various aspects of brushless motors, including construction, types, benefits, drawbacks, applications, & working principles, and compare them with their traditional counterparts, brushed DC motors.

More About  BLDC Motor

Modern drive technology has greatly benefited from the introduction of brushless DC motors, also referred to as BLDC motors.

Due to their quick rise in popularity, they are being used in more and more industries, including consumer appliances, automotive, industrial automation, chemical and medical, aerospace, and instrumentation.

What is a Brushless DC Motor?

• BLDCs, or brushless DC motors, are permanent magnet synchronous electric motors powered by direct current (DC) electricity. They function as an electronically controlled commutation system as opposed to a mechanically operated one.
• Another name for BLDC motors is trapezoidal permanent magnet motors.
• As the name suggests, BLDC motors are electronically commutated rather than using brushes for this purpose.

Construction of BLDC Motor

The motor’s construction is pretty much the same as that of a conventional DC motor and a three-phase induction motor. Like all motors, this one has a stator and a rotor.

There are several physical arrangements in which BLDC motors can be built. These motors can have a single-phase, two-phase, or three-phase configuration, depending on the stator windings. The most commonly utilized BLDC motors, however, are three-phase models with permanent magnet rotors. The construction details of BLDC motors are displayed in Figs. 2a and 2b.

Stator

A BLDC motor’s stator is composed of layered steel laminations that support the windings. These windings are positioned inside the stator’s inner perimeter in slots that have been axially carved. It is possible to organize these windings in a delta or star pattern. On the other hand, the majority of BLDC motors use a three-phase star-connected stator. One or more coils are inserted into each slot in each winding, which is made up of several interconnected coils. All of these windings are spaced out over the stator’s perimeter to create an even number of poles.

Depending on the capacity of the power source, the stator needs to be selected with the appropriate voltage rating. BLDC motors with a voltage of 48 V or less are recommended for robotics, automotive, and small electrical applications. Motors rated at 100 V or greater are utilized for automation systems and industrial applications. The BLDC motor’s stator construction details are displayed in Fig. 3a.

Rotor

Permanent magnets are used in the rotor of BLDC motors. Depending on the requirements of the application, the rotor’s pole count can range from two to eight pole pairs with alternate south and north poles. For the motor to reach its maximum torque, a high material flux density is required. To generate the necessary magnetic field density, the rotor needs to be made of the right magnetic material.
Although ferrite magnets are cheap, their flux density is low for a given volume. New designs frequently use magnets made of rare earth alloys. Among these alloys are ferrite and boron (NdFeB), neodymium (Nd), and samarium cobalt (SmCo).

Various core configurations, including a circular core with a permanent magnet on the circumference or a circular core with rectangular magnets, can be used to build the rotor. Different rotor constructions are displayed in Fig. 4.a. Basically, there are two approaches to building a BLDC motor: one is to put the windings outside the core and the rotor outside with the windings inside. Under the former setup, the motor’s rotor magnets function as an insulator, slowing down the motor’s rate of heat dissipation and requiring less current to run. Usually, it is utilized by fans. The motor dissipates more heat in the latter configuration, which raises the torque of the motor. Hard disk drives make use of it. The BLDC motor’s rotor construction details are displayed in Fig. 3b.

Position Sensors(Hall Sensors)

A BLDC motor’s commutation is electronically controlled because it doesn’t have brushes. The rotor windings must be energized sequentially to rotate the motor. And the accurate energization of a specific set of stator windings requires knowledge of the rotor’s position or its North and South poles.

To detect the position of the rotor and convert it into an electrical signal, a position sensor—typically a Hall sensor—is employed. Hall sensors operate based on the Hall effect. The stator windings must be activated sequentially to rotate the motor because the BLDC motor’s commutation is regulated electronically.

Recognition of the rotor position is required before activating a certain stator winding. Therefore, the rotor position is sensed by the Hall Effect sensor that is incorporated into the stator. The rotor’s position is sensed by the majority of BLDC motors using three hall sensors that are built into the stator. The location of the sensor in the BLDC motor is displayed in below.

The data from the Hall sensor enables the rotor position and stator armature excitation to be synchronized. Whenever the rotor poles approach any given sensor, they produce both low and high signals. The response of these three sensors together can be used to identify the precise commutation sequence for the stator winding.

Working of BLDC Motor

• Similar to a traditional DC motor, a BLDC motor operates on the same principle, which is the law that states that any time a current-carrying conductor is placed in a magnetic field, it experiences force. The magnet will encounter an equal and opposite force as a result of the reaction force. When using a BLDC motor, the permanent magnet moves while the current-carrying wire remains motionless.
• It becomes an electromagnet and begins to create a uniform field in the air gap when the stator coils are electrically switched by a supply source. Despite the DC supply source, switching produces an AC voltage waveform with a trapezoidal shape. The rotor keeps rotating because of the force exerted by the interaction between the permanent magnet rotor and the electromagnet stator.
• Corresponding windings that are energized as the North and South poles are switched as high and low signals. The motor rotates because the north and south poles of the permanent magnet rotor line up with the stator poles.

Types of BLDC Motor

Electronic and electrical appliances, cars, robotic devices, industrial machinery, and other surroundings all use various kinds of BLDC motors. Brushless DC motor types can be categorized as follows:

According to Design

Based on design, brushless DC motors can be categorized as follows:

Internal Rotor/In-runner BLDC Motor

The rotating component (rotor) of this kind of BLDC motor is housed inside a group of magnetic coils (stator). Since the stator coils of this brushless DC motor are mounted on the motor’s casing, heat can be dissipated through conduction. Applications that demand greater RPM characteristics are best suited for an in-runner brushless DC motor since it can readily reach peak speeds. These motors frequently have a rotor with few poles. Therefore, at slower speeds, their performance declines.

External Rotor/Out-runner BLDC Motor

The in-runner type and this out-runner BLDC motor are essentially the opposite. It also goes by the name “outer rotor BL motor” and revolves around an outer case around a stationary inner component. More permanent magnet poles are typically used on the rotor of out-runner BLDC motors. Increased torque and more seamless operation result from this. The out-runner brushless DC motor’s poor speed is its primary drawback. Consequently, low-speed, high-torque applications are a better fit for these kinds of motors.

Depending on the Type of Sensor Used

Based on the type of sensor used in BLDC, it is as follows:

Brushless DC Motor with Sensor

A BLDC motor that uses sensors to obtain information about the rotor position is called a sensored BLDC motor. At reduced speeds, these BL motor types provide consistent performance. For a smooth rotation, the sensors deliver precise data at lower rpm. At greater speeds, the primary disadvantage of sensored motors reveals itself when the sensor feedback becomes unreliable. Severe circumstances like dusty or hot surroundings also have an impact on the sensors and, consequently, the functioning of the motors. The optimum uses for these motors are low-rpm ones.

Brushless DC Motor without Sensor

There are no sensors used in this kind of motor. Rather, the rotor position is determined by the controller using the back electromotive force produced in the stator coils. At high speeds, these brushless DC motor types provide the finest performance. Because they don’t rely on sensors, you can also utilize them in challenging environments. At low speeds, when the back EMF is too low for the controller to read, or when beginning from a stationary position, their shortcomings become apparent. These motor types work well in tough environments and at high speeds.

Depending on the Number of Poles

Based on the number of poles used in BLDC, it is as follows:

Single-pole BLDC Motor

A single set of poles, North and South, make up the rotor of a single-pole BLDC motor. There are benefits and drawbacks to this kind of brushless DC motor design. The motor can rotate at extremely high speeds, which is the first advantage. The disadvantage of single-pole motors is that their efficiency and rotational stability are negatively impacted at lower rpms due to a large decline in performance. It is therefore ideal to employ them in high-speed applications.

Multi-pole BLDC Motor

Several poles, typically up to eight, are used on the rotor in multipole motors. These are positioned so that the opposing poles face one another, as was previously indicated. A smoother rotation is achieved at the cost of speed when there are more poles. These BL motors are typically utilized in low-speed applications that call for high torque levels because they are unable to reach high rpm levels.

According to the Power Signal Type

BLDC motors are frequently arranged according to the power and back EMF voltage signals. The discussion of this category’s motors follows.

Sinusoidal BLDC motor

These brushless DC motor types use a sinusoidal-shaped duty cycle signal. Using a current that follows a smooth sinusoidal curve, the controller attempts to power all of the stator windings in this commutation approach. As a result, the torque ripple effect that is typical of trapezoidal motors is canceled. Generally operating at lower speeds, a sinusoidal BLDC motor provides smooth performance. The torque decreases with increasing speed. They are thus more suited for circumstances involving slow speeds.

Trapezoidal BLDC Motor

A power signal in the shape of a trapezoid is used by a trapezoidal BLDC motor. Compared to the sine wave type, this is a straightforward commutation approach. Using this procedure, the third terminal is left unplugged while one pair of terminals is powered at a time. The torque ripple effect that the signal creates is a disadvantage, despite its simplicity. Because of this, the motor runs less smoothly, especially at lower rpm. These motors are more efficient than sinusoidal types at higher RPMs, making them suitable for applications that primarily require high speeds.

Advantages of Brushless DC Motor

1. There are no related issues with the mechanical commutator.
2. Longer lifespan due to the commutator system’s lack of need for inspection or maintenance.
3. Excellent efficiency as a result of the permanent magnet rotor.
4. Because there are no brushes to restrict speed, the machine operates at a high pace even when it is filled or empty.
5. Less bulk and weight compared to induction AC and brushed type DC motors.
6. Reduced interference from electromagnetic sources.
7. Lower noise because there are no brushes.
8. A stator’s carrying windings and low inertia contribute to its higher dynamic response.

Disadvantages of Brushless DC motor

1. Because an electronic controller is needed, these motors are expensive.
2. Electronic control options, particularly for small BLDC motors.
3. Needs sophisticated driving circuitry.
4. Extra sensors are required.

Applications of Brushless DC Motor (BLDC)

Brushless DC motors (BLDC) are utilized in a wide range of industries, including industrial control, automotive, aviation, automation systems, and healthcare equipment, for a variety of application needs, including variable loads, constant loads, and positioning applications.

BLDC motors are specifically used in the following applications:

• DVD/CD players and computer hard drives.
• Hybrid automobiles, electric bikes, and electric cars.
• Basic belt-driven systems, CNC machine tools, and industrial robots.
• Dryers, compressors, and washing machines.
• Blowers, pumps, and fans.

Comparison between Brushless DC Motors (BLDC) and Brushed DC Motors

Brushless DC motors, which represent efficiency, accuracy, and dependability, are a monument to innovation in an era of rapidly advancing technology. Their broad industry acceptance creates a clear image of a future in which BLDC motors drive society to become more technologically advanced and energy-conscious.

Read Also:
DC Motor- Classification, Working Mechanism, Applications & Advantages
Induction Motor | Asynchronous Motor – Type, Features, How does it Works