Brushless DC Motors

Brushless DC Motors(BLDCMs)

Group MembersMalik Muhammad Kamal(Basics of DC Motor)Haris Zaman(Construction of BLDCMs)Haseeb Akhtar(Controller Circuit)Malik Muhammad Moin(Applications)Motor Basics

BLDCMs Introduction A BLDC is simply a normal dc motor turned inside out, that means the coil is on the out side and the magnets are insideBLDCMs are generated by virtually inverting the stator and rotor of PM DC motors.The stator consists of several coils which current is led through Creating a magnetic field that makes the rotor turns

Introduction ContBasically BLDCMs are equivalent to the Permenant Megnet AC Motors except one difference The Haul Sensor.

CONSTRUCTIONof BLDCMs

The brushless motor, unlike the DC brushed motor, has the permanent magnets glued on the rotor.

It has usually 4 magnets around the perimeter. The stator of the motor is composed by the electromagnets, usually 4 of them, placed in a cross pattern with 90oangle between them.

The major advantage of the brushless motors is that, due to the fact that the rotor carries only the permanent magnets, it needs of NO power at all. No connection needs to be done with the rotor, thus, no brush-commutator pair needs to be made! This is how the brushless motors took their name from.

Construction Cont Stator consists of stacked steel laminations with windings placed in the slots that are axially cut along the inner periphery

Rotor is made of permanent magnet and can vary from two to eight pole pairs with alternate North (N) and South (S) poles. Ferrite magnets and Rare earth alloy magnets are used in rotor

10As there is no Brushes and hence no commutators ,the current direction of the conductor on the stator controlled electronically.Hall sensor used to determine the position during commutationThese Sensors sens the position of the coil acuratly and hence direction of current remain in one side due to control circuit.

The Haul SensorHaul EffectWhen a magnetic field applied to a system with electric current a hall voltage Perpendicular to the field and to current is generated

WorkingHalls Sensors sense the position of the coils

The Decoder Circuit turns appropriate switches on and off

The voltage through the specific coils turns the motor

Animation

Applications of BLDCMsSpeed Torque Characteristics

General ApplicationsSingle-speed For single-speed applications, induction motors are more suitable, but if the speed has to be maintained with the variation in load, then because of the flat speed-torque curve of BLDC motor, BLDC motors are a good fit for such applications.

Adjustable speed BLDC motors become a more suitable fit for such applications because variable speed induction motors will also need an additional controller, thus adding to system cost. Brushed DC motors will also be a more expensive solution because of regular maintenance.

Applications ContPosition control Precise control is not required applications like an induction cooker and because of low maintenance; BLDC motors are a winner here too. However, for such applications, BLDC motors use optical encoders, and complex controllers are required to monitor torque, speed, and position.

Low-noise applications Brushed DC motors are known for generating more EMI noise, so BLDC is a better fit but controlling requirements for BLDC motors also generate EMI and audible noise. This can, however, be addressed using Field-Oriented Control (FOC) sinusoidal BLDC motor control.

Industrial ApplicationsConsumer: Hard Drives, CD/DVD Drives, PC Cooling Fans, toys, RC airplanes, air conditionersMedical: Artificial heart, Microscopes, centrifuges, Arthroscopic surgical tools, Dental surgical tools and Organ transport pump system.Vehicles: electronic power steering, personal electric vehicles