In our traditional brushed motors brushes are employed in order to switch the central moving rotor with respect to the surrounding stationery permanent magnet stator. Brushes become imperative because the rotor is made using electromagnets that needs power to operate but since it also needs to rotate things become clumsy and brushes become the only alternative for supplying power to the rotating electromagnetic rotor.
The stator is made up of a set of electromagnets while the rotor has permanent magnets affixed across its perimeter at a certain calculated positions. The above explanation may be understood with the help of the following basic illustration and then through an elaborate design in the subsequent images. We have learned and know quite a few interesting things about magnets and how these devices interact. We know that a North Pole of the magnet attracts the south Pole of another magnet while like poles repel.
In the above shown diagram we see a disc with an embedded magnet at its edge shown in red color which is positioned with north pole facing outward, and also an electromagnet placed at a parallel proximity to the circular edge of the disc which produces a south magnetic field when energized. Now assuming the arrangement is positioned as shown in the first upper diagram with the electromagnet in a deactivated state.
In this position as soon as the electromagnet is activated with an appropriate DC input it attains and generates a south magnetic field influencing a pulling force over the disc magnet which in turn forces the disc to rotate with some torque until its permanent magnet comes in line with the electromagnets opposite lines of flux. Now let's see how actually the above concept is implemented using Hall effect sensors in order to sustain a continuous motion over the rotor.
The rotor could be seen having a couple of permanent magnets fixed at the periphery which have south pole as the influencing lines of flux, the central stator is a strong electromagnet which is designed to generate an equivalent strength of North Pole magnetic flux when energized with an external DC.
We can also visualize a hall sensor situated near one of the corners of the inner rotor periphery. The hall effect fundamentally senses the magnetic field of the rotating rotor and feeds the signal to a control circuit responsible of powering the stator electromagnets. Referring to the upper position we see the blank area which is void of any magnetic field of the rotor in close contact with the hall sensor keeping it in a switched OFF state.
At this instant, the switch off signal from the hall effect informs the control circuit to switch ON the electromagnets, which instantly induces a pulling effect on the rotor south pole standing just round the corner. When this happens the South pole comes down surging producing the required torque on the rotor and tries to align itself in line with the north pole of the electromagnet. However in the process the south pole of the rotor also pulls itself near to the hall sensor as shown in the lower diagram which immediately detects this and switches ON informing the control circuit to switch OFF the electromagnets.
Switching off of the electromagnets at the right moment as signaled by the hall effect sensor prohibits stalling and hampering of the rotor motion, rather allows it to carry on with the motion through the generated torque until the previous position begins shaping up, and until the hall sensor yet again "feels" the blank area of the rotor and gets switched OFF repeating the cycle. In order to attain exceptionally higher torques more magnets and sets of electromagnets are employed in other higher efficiency brushless motors wherein more than one hall effect sensor may be seen for implementing multiple sensing of the rotor magnets so that different sets of electromagnets could be switched at the preferred correct sequence.
So far we have understood the basic working concept of BLDC motors and learned how a Hall sensor is used for activating the motor's electromagnet through an external attached electronic circuit for sustaining a continuous rotating motion of the rotor, in the next section we will study regading how BLDC driver circuit actually work for controlling BLDC motors.
The method of implementing a fixed stator electromagnet and a rotating free magnetic rotor ensures enhanced efficiency to BLDC motors compared to the traditional brushed motors which have exactly the opposite topology and therefore require brushes for the motor operations.
The use of brushes makes the procedures relatively inefficient in terms of long life, consumption and size. Although, BLDC types may be the most efficient motor concept, it has one significant drawback that it requires an external electronic circuit for operating it. However, with the advent of modern ICs and sensitive Hall sensors this issue now seems to be quite trivial when compared with the high degree of efficiency involved with this concept.
In the present article we are discussing a simple and basic control circuit for a four magnet, single hall sensor type BLDC motor. The motor operation may be understood by referring to the following motor mechanism diagram:.
The image above shows a basic BLDC motor arrangement having two sets of permanent magnets across the periphery of an external rotor and two sets of central electromagnet A,B,C,D as the stator. To be precise, let's assume the position shown in the above scenario with A and B in a switched ON state such that side A is energized with South pole while side B energized with North Pole.
This would mean that the side A would be exerting a pulling effect over its left blue North pole and a repelling effect on its right side south pole of the stator, similarly the side B would be pulling the lower red south pole and repelling the upper north pole of the rotor Let's also assume that in the above situation the Hall sensor is in a deactivated state since it may be a "south pole activated" Hall sensor device.
The above explained switching of the electromagnets in response to the Hall sensor triggering signal can be very simply implemented using the following straightforward BLDC control circuit idea. The situation is toggled alternately, continuously as long as power remains applied keeping the BLDC rotating with the required torques and momentum.The BLDC motor is electrically commutated by power switches instead of brushes.
That is why these motors are, sometimes, also referred as Electronically Commutated Motors. Like any other electric motor, a BLDC motor also has a stator and a rotor. Here we will consider Stator and Rotor each separately from construction point of view. There are three types of the BLDC motor:. Stator for each type has the same number of windings. The single-phase and three-phase motors are the most widely used.
The simplified cross section of a single-phase and a three-phase BLDC motor is shown in figure below. The rotor has permanent magnets to form two magnetic pole pairs, and surrounds the stator, which has the windings.
A single-phase motor has one stator winding wound either clockwise or counter-clockwise along each arm of the stator to produce four magnetic poles as shown in above figure. A three phase BLDC motor has three windings. Each phase turns on sequentially to make the rotor revolve. A rotor consists of a shaft and a hub with permanent magnets arranged to form between two to eight pole pairs that alternate between north and south poles. Figure below shows cross sections of three kinds of magnets arrangements in a rotor.
BLDC Motor operation is based on the attraction or repulsion between magnetic poles. Using the three-phase motor as shown in figure below, the process starts when current flows through one of the three stator windings and generates a magnetic pole that attracts the closest permanent magnet of opposite pole.
The rotor will move if the current shifts to an adjacent winding. Sequentially charging each winding will cause the rotor to follow in a rotating field. The torque in this example depends on the current amplitude and the number of turns on the stator windings, the strength and the size of the permanent magnets, the air gap between the rotor and the windings, and the length of the rotating arm. Notify me when new comments are added. Lower acoustic noise.
Smaller and lighter. Greater dynamic response. Better speed versus torque characteristics. Higher speed range. Longer life.Brushless DC motors BLDC have been a much focused area for numerous motor manufacturers as these motors are increasingly the preferred choice in many applications, especially in the field of motor control technology. BLDC motors are superior to brushed DC motors in many ways, such as ability to operate at high speeds, high efficiency, and better heat dissipation.
They are an indispensable part of modern drive technology, most commonly employed for actuating drives, machine tools, electric propulsion, robotics, computer peripherals and also for electrical power generation. With the development of sensorless technology besides digital control, these motors become so effective in terms of total system cost, size and reliability.
A brushless DC motor known as BLDC is a permanent magnet synchronous electric motor which is driven by direct current DC electricity and it accomplishes electronically controlled commutation system commutation is the process of producing rotational torque in the motor by changing phase currents through it at appropriate times instead of a mechanically commutation system.
BLDC motors are also referred as trapezoidal permanent magnet motors. Unlike conventional brushed type DC motor, wherein the brushes make the mechanical contact with commutator on the rotor so as to form an electric path between a DC electric source and rotor armature windings, BLDC motor employs electrical commutation with permanent magnet rotor and a stator with a sequence of coils.
In this motor, permanent magnet or field poles rotates and current carrying conductors are fixed. The armature coils are switched electronically by transistors or silicon controlled rectifiers at the correct rotor position in such a way that armature field is in space quadrature with the rotor field poles. Hence the force acting on the rotor causes it to rotate.
Hall sensors or rotary encoders are most commonly used to sense the position of the rotor and are positioned around the stator. The rotor position feedback from the sensor helps to determine when to switch the armature current. This electronic commutation arrangement eliminates the commutator arrangement and brushes in a DC motor and hence more reliable and less noisy operation is achieved.
Due to the absence of brushes BLDC motors are capable to run at high speeds. The efficiency of BLDC motors is typically 85 to 90 percent, whereas as brushed type DC motors are 75 to 80 percent efficient.
There are wide varieties of BLDC motors available ranging from small power range to fractional horsepower, integral horsepower and large power ranges. BLDC motors can be constructed in different physical configurations. Depending on the stator windings, these can be configured as single-phase, two-phase, or three-phase motors. However, three-phase BLDC motors with permanent magnet rotor are most commonly used.
The construction of this motor has many similarities of three phase induction motor as well as conventional DC motor. This motor has stator and rotor parts as like all other motors.
Stator of a BLDC motor made up of stacked steel laminations to carry the windings. These windings are placed in slots which are axially cut along the inner periphery of the stator. These windings can be arranged in either star or delta. However, most BLDC motors have three phase star connected stator.
Each winding is constructed with numerous interconnected coils, where one or more coils are placed in each slot. In order to form an even number of poles, each of these windings is distributed over the stator periphery.
Introduction to Brushless DC Motors (BLDC Motor)
The stator must be chosen with the correct rating of the voltage depending on the power supply capability.
For robotics, automotive and small actuating applications, 48 V or less voltage BLDC motors are preferred. For industrial applications and automation systemsV or higher rating motors are used. BLDC motor incorporates a permanent magnet in the rotor. The number of poles in the rotor can vary from 2 to 8 pole pairs with alternate south and north poles depending on the application requirement. In order to achieve maximum torque in the motor, the flux density of the material should be high. A proper magnetic material for the rotor is needed to produce required magnetic field density.Their rapid gain in popularity has seen an increasing range of applications in the fields of Consumer Appliances, Automotive Industry, Industrial Automation, Chemical and Medical, Aerospace and Instrumentation.
Even though they have been used for drives and power generation for a long time, the sub kilowatt range, which has been dominated by Brushed DC Motors, has always been a grey area.
But the modern power electronics and microprocessor technology has allowed the small Brushless DC Motors to thrive, both in terms price and performance. In conventional Brushed DC Motors, the brushes are used to transmit the power to the rotor as they turn in a fixed magnetic field. As mentioned earlier, a BLDC motor used electronic commutation and thus eliminates the mechanically torn brushes. The main design difference between a brushed and brushless motors is the replacement of mechanical commutator with an electric switch circuit.
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 three configurations: single phase, two phase and three phase. Out of these, the three phase BLDC is the most common one.
It is made up of stacked steel laminations with axially cut slots for winding. The winding in BLDC are slightly different than that of the traditional induction motor. Additionally, based on the coil interconnections, the stator windings are further divided into Trapezoidal and Sinusoidal Motors. In a trapezoidal motor, both the drive current and the back EMF are in the shape of a trapezoid sinusoidal shape in case of sinusoidal motors. Usually, 48 V or less rated motors are used in automotive and robotics hybrid cars and robotic arms.
Based on the application, the number of poles can vary between two and eight with North N and South S poles placed alternately.
The following image shows three different arrangements of the poles. In the first case, the magnets are placed on the outer periphery of the rotor. The second configuration is called magnetic-embedded rotor, where rectangular permanent magnets are embedded into the core of the rotor.
In the third case, the magnets are inserted into the iron core of the rotor. In order to rotate the motor, the windings of the stator must be energized in a sequence and the position of the rotor i. A Position Sensor, which is usually a Hall Sensor that works on the principle of Hall Effect is generally used to detect the position of the rotor and transform it into an electrical signal. By combining the results from the three sensors, the exact sequence of energizing can be determined.
Consider the following setup of three windings in the stator designated A, B and C.A commutator-brushes arrangement helps in achieving unidirectional torque in a typical dc motor.
Obviously, commutator and brush arrangement is eliminated in a brushless dc motor. That is why these motors are, sometimes, also referred as 'electronically commutated motors'. Just like any other electric motor, a BLDC motor also consists of two main parts a stator and a rotor. Permanent magnets are mounted on the rotor of a BLDC motor, and the stator is wound for a specific number of poles.
Also, a control circuit is connected to the stator winding. This is the basic constructional difference between a brushless motor and a typical dc motor.
A typical controller provides a three-phase frequency-controlled supply to the stator winding. The supply is controlled by logical control circuits and energizes specific stator poles at a specific point of time.
Brushless DC (BLDC) Motor - Construction and Working
This can be understood from the below animations about working of BLDC motors. Regardless of these types, note that the permanent magnets are always mounted on the rotor and winding on the stator. Stator windings of a BLDC motor are connected to a control circuit an integrated switching circuit or inverter circuit. The control circuit energizes proper winding at the proper time, in a pattern which rotates around the stator. Permanent magnets on the rotor try to align with the energized electromagnets of the stator, and as soon as it aligns, the next electromagnets are energized.
Thus, the rotor keeps running. The animations below will give you a clear idea of 'how a brushless DC motor works? Despite this, there are many applications where BLDC motors dominate —. Recieve free updates Via Email! Home Electrical machines Power system Ask a question Contact electricaleasy.
Electrical motors have been developed in various special types, such as stepper motorsservo motorspermanent magnet motorsetc. We have a lot of choices to choose a motor that is most suitable for our application. A Brushless DC motor or BLDC motor is a type that is most suitable for applications that require high reliability, high efficiency, more torque per weight, etc. This article explains about BLDC motors in details.I followed your instructions for generating a direct link for mobile devices.
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Brushless DC Motor (BLDC) – Construction, Working Principle & Applications
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