BRUSHLESS DC MOTOR[BLDC MOTOR]

WHAT IS BRUSH-LESS DC MOTOR ?

Also known as BLDC motor or BL motor, it is the DC motor which does not have brushes. Motor is the heart of an Electric Vehicle. It is called Brushless because it doesn’t have brushes and commutator arrangements. Here the commutation is done electronically.

PRINCIPLE OF BLDC MOTOR:

The working principle of BLDC motor is similar to Brushed DC motor. The reversal of current in Brushed DC motor is done by Commutator and Brushes whereas in BLDC motor sensors are used, mostly hall-effect sensors. The hall-effect sensors generate a high or low signal whenever rotor magnetic poles cross the hall sensors, which can be used to detect the position of the shaft.

TYPES OF BLDC MOTORS:

They are classified based on designing and their working procedure is the same.

  • Outer rotor design
  • Inner rotor design
BLDC Motor Types

OUTER ROTOR DESIGN: The rotor of the motor is situated outside and it surrounds the stator which is located in the center of the motor has multi-phase winding. The windings are fed with current and are controlled(commutated) to effect rotation of the rotor. There is no need of external gear system in this type of design and in few instances the motor itself comes with inbuilt gears. Therefore, without any gear system this design makes the device less bulky.  The magnets present in the rotor acts as an insulator and will not allow the heat to dissipate from the motor. Outer rotor designed motor has low torque and operated at low current rates.

INNER ROTOR DESIGN : As in the image the rotor is situated in the centre of the motor and is surrounded by the stator winding. The rotor magnet does not shield the heat inside and the heat will be dissipated effortlessly, thus increasing the torque.

WORKING OF BLDC MOTOR

Working of BLDC Motor

The BLDC motor has 2 main parts rotor and stator. The rotor is the permanent magnet and is rotating part. The stator is the armature winding and is the stationary part. In BLDC motor coils do not rotate as in Brushed DC motor instead they are fixed onto the stator. There is no need of commutator and brushes since coils are static.

Refer https://futuretronlabs.in/blog/index.php/2019/09/25/electric-motor/ to know more about the working of an electric motor.

Mechanical rotation is produced when the magnetic field generated by the permanent magnets(rotor) comes in contact with the field induced by the current in the stator windings. The magnitude and direction of the current into the coils are adjusted to control the rotation.

 Hall effect sensors are mounted on the stator or rotor. As the rotor rotates the hall effect sensors senses the magnetic field and produces a high signal for one pole or low signal for opposite pole. These sensors are connected to the Electronic control unit. Electronic control unit switches the supply voltage between the stator winding as the rotor rotates and energize the correct winding at correct time in such a way that it rotates the rotor around the stator. According to these combinations of signals electronic unit will decide the next commutation sequence or interval to activate.

Some of the advantages of Brushless DC motors are they are highly efficient, exceptional controllability, produce high torque, higher speed range compared to other motors, Operating life is long due to absence of electrical friction losses, Operation is noise-less, high dynamic response. It has power-saving advantages also. Due to its traction characteristics they are most preferred motors in electric vehicle applications.

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BRUSHED DC MOTOR

WHAT IS BRUSHED DC MOTOR??

One of the simplest types of the motor is the brushed DC motor. The concept behind this motor is when the electrical current is passed through the coils that are arranged inside a fixed magnetic field [N and S]. The current generates magnetic fields in the coils, each coil is repelled from the like pole and attracted towards the unlike pole of the fixed field which causes the coil assembly to rotate. To continue this rotation, the current must be reversed so that the coil polarity will be continuously changed producing the coils to continue chasing the unlike fixed poles.

BRUSHED DC MOTOR

The main components which make Brushed DC motor unique from other motors are brushes and commutator. The power to the coils is provided by the conductive brushes which are in contact with the rotating commutator. Commutator is used to switch the current in the motor windings, and is placed on the axle of the rotor. When the power is given to the brushes which is in contact with commutator, provides power to the windings. This produces the magnetic field around the rotor [Armature]. The rotation of the commutator causes the current to reverse through the coils.

The rotor is pushed away by the stator magnet that is -left part of the rotor is pushed away by left stator magnet towards the right stator magnet; -and the right part of the rotor is pushed away by the right stator magnet towards the left stator magnet. Hence motor is made to rotate continuously by regularly changing the polarity of the magnetic field around the rotor.

Advantages of Brushed DC motor are they are low-cost motors, Easy to Control, Outputs high torque at low speeds.

Disadvantages are maintenance cost is high since brushes and commutators wear quickly and should be replaced when required, electrical noise is more, limited maximum speed because excessive speed will increase the heat.

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ELECTRIC MOTOR

What is an Electric Motor??

An Electric Motor  is an  electrical machine that converts electrical energy into mechanical energy.

The History behind an Electric Motor:

The connection between electricity, magnetism, and movement was discovered in 1820 by French physicist Andre-Marie Ampere (1775–1867) and that is the basic science behind an electric motor.

The discoverers who converted this scientific discovery into a practical bit of technology to power electric motors were Englishmen Michael Faraday (1791–1867) and William Sturgeon (1783–1850) and American Joseph Henry (1797–1878). 

The basic idea of an electric motor is simple, electricity is given at one end and at the other end, an axle(metal bar) rotates giving the power to drive any kind of machines.

The principle behind the working of an electric motor is when a current-carrying conductor is placed in a magnetic field it experiences a magnetic field and starts rotating according to the direction given by Fleming’s Left-Hand Rule for a motor.

There are many types of electric motor available in the market and the choice of these motors are very important. Selection of these motors is based on voltage, operation, and application.

TYPES:

Motors are classified based on the power type that is AC or DC and their method for generating rotation.

DC MOTORS

  • Brushed DC motor
  • Brushless DC motor
  • Stepper (STP)

AC MOTORS

  • Induction motor (IM)
  • Synchronous Motor (PM)

Both types of motor have their own advantages and disadvantages:

Comparison between AC and DC motor

IMPORTANT PARTS OF AN ELECTRIC MOTOR:

Important Parts of an Electric Motor

Armature: It is the power generating part in an electric motor. It can be a  rotating part or the stationary part of the machine.  The armature[ABCD] has the rectangular iron core wrapped by copper wire through which current is passed and is placed between the two poles of a magnet. The armature has an axle to which commutator is attached.

Commutator: They are the split rings which reverses the direction of the current. They connect the brushes and coil and are made up of copper. The purpose of the commutator is to make sure that the current direction in the coil reverses every half time so that one side of the coil is pushed downwards and another side of the coil is pushed upwards. The contacts of the commutator are linked to the axle of the armature so they rotate with the coil.  In the above figure, commutator rings are denoted as C1 and C2.

Brushes: They are the two pieces of metal or carbon. One end of the brush is connected to the commutator and other ends of the brushes are connected to the positive and negative terminal of the battery respectively. In the above figure, Brushes are denoted as B1 and B2.

Working of an Electric Motor:

An electric motor uses the magnetic push to rotate the current-carrying conductor.

Magnets S and N will generate the magnetic field that will rotate the current-carrying conductor. Instead of inserting the current-carrying wire, a current-carrying loop [rectangular loop] is introduced as in the figure. Each side of the coil will experience the force and hence the coil starts rotating. To find the direction of the force in each side of the loop Flemings Left-Hand rule for motors(also called motor rule) is used.

Fleming’s Left-Hand Rule:

Fleming’s Left Hand Rule

Hold your thumb, fore and center finger of your left hand such that three fingers are at right angles to each other.

If you point the center finger in the direction of the current and the forefinger in the direction of the field, your thumb will show the direction of motion.

  • Fore-finger = Field
  • Center finger = Current
  • Thumb finger= Motion
Working of an Electric Motor

To begin with, the plane of the rectangular coil ABCD is made parallel to the magnetic field by placing the coil in the horizontal position. Electric current is passed through the rectangular coil ABCD, which enters at A and leaves at D as shown in the figure. When the current is passed AB and CD side of the coil which is perpendicular to the direction of the magnetic field experience force according to Fleming’s left-hand rule. As the current passing through AB and CD of the coil are in the opposite direction, the forces acting on them will also be opposite. Hence forces push AB in downward direction and CD in the upward direction. Thus the coil starts rotating in the anticlockwise direction.

The commutator rings C1 and C2 change their contact from brushes B1 and B2 respectively when the coil completes its half rotation. Because of this, the direction of current in the rectangular coil ABCD is reversed, due to which the direction of forces in the coil is also reversed. Hence side AB is now pushed in upward and CD in the downward direction. Similarly, the whole process is repeated for the continuous rotation of the coil.

Advantages of an Electric Motor:

  • For the same horse-power rating, the initial cost of an electric motor is less compared to fuel engines.
  • An electric motor has comparatively few moving parts and hence longer lifespan.
  • Minimum maintenance is required.
  • Electric motors don’t require fuel, hence there is no need for engine oil maintenance, also no greenhouse gas emissions.
  • Electric motors are highly-efficient with the ratings that range from 50% to 95%.
  •  Wear and tear problems are less.

Refer https://futuretronlabs.in/blog/index.php/2019/08/29/advantages-of-ev/ to know more about the advantages of an Electric vehicle.

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