brush less dc motor

RVR&JC COLLEGE OF ENGINEERING

BLDCMBRUSHLESS DC

MOTOR

B HARISH

CONTENTS INTRODUCTION WHY BLDC? PRINCIPLE CONSTRUCTION WORKING ADVANTAGES DISADVANTAGES APPLICATIONS CONCLUSION

INTRODUCTION

MOTORS

Brushed motor Brushless motor

Inrunner

Outrunner

BRUSHED MOTOR It is a machine which converts electrical

energy to mechanical energy. Above electrical input can be given to the

brushes and followed by commutator.

BRUSHLESS MOTOR These are also known as electronically

brushless commutated motors. These are powered by direct-current

electricity and having electronic commutation systems, rather than mechanical commutators and brushes.

BLDC motors come in single phase, two phase and three phase configurations. Out of these three phase motors are the most popular and widely used

WHY BLDC ?BRUSHED BRUSHLESS

Brushess &commutator requires maintainence.

There is a mechanical contact between the brushes & commutator.

Rotors position is automatically detected by brushes

There are no brushess and commutator.

Elecronic switching using transistors.

Rotor position is detected by hall sensor ,optical encoder.

WORKING PRINCIPLE It works on the principle based on

“simple force of attraction between the permanent magnet and electromagnet”

CONSTRUCTION Just like any other electric motor, a BLDC

motor also has a stator and a rotor. Permanent magnets are mounted on the rotor of a BLDC motor, and stator is wound with specific number of poles. This is the basic constructional difference between a brushless motor and a typical dc motor.

There can be two types of BLDC motor on the basis of construction : (i) inner rotor design & (ii) outer rotor design.

IN RUNNER OUT RUNNER

Simple construction of outrunner BLDCM

STATOR ROTOR

WORKINGThe stator has a coil arrangament as shownIt has three coils,named as A,B&C.

When the coil A is energised the opposite poles of a rotor are attracted to each other,as a result the rotor poles move near to the energised stator

As the rotor the rotor nears the coil A,coil B is energised.As the rotor nears the coil B, coil C is energised.After that coil A is again energised with opposite polarity

This process is repeated and the rotor is continued to rotate, the DC current required the each coil is shown in the graph.

Even though this motor works, it has one drawback. You can notice that, at any instant only one coil is energized. The 2 dead coils greatly reduce the power output of the motor. Here is the trick to overcome this problem. When the rotor is in this position, along with the first coil, which pulls the rotor, you can energize the coil behind it such a way that, it will push the rotor.

With this configuration 2 coils need to be energized separately, but by making a small modification to the stator coil, we can simplify this process. Just connect one free end of the coils together, When the power is applied between coils A and B, let’s note the current flow through the coils. it is clear that, the current flow is just like the separately energized state.

The current form required for the complete 360 degree rotation is shown in the graph below.

 The combined effect produces more torque and power output from the motor. The combined force also makes sure that a BLDC has a beautiful, constant torque nature. Such torque nature is difficult to achieve in any other type of motors.

That’s how a BLDC works. But, you might have some intriguing doubts in your mind. How do I know which stator coils to energize? How do I know when to energize it, so that I will get a continuous rotation from the rotor? In a BLDC we use an electronic controller unit (ECU) for this purpose. A sensor determines the position of the rotor, and based on this information the controller decides, which coils to energize.

The schematic figure above shows, how the ECU controls task of energizing the coil. This task is known as commutation. Most often, a Hall-effect sensor is used for this purpose. The Hall-effect sensor is fitted on the back of the motor as shown in the Fig

ADVANTAGES No brushes or commutators to wear out No generation of EMI High torque to inertia ratio No winding on the motor but supported

by housing High efficiency(up to 97%) No sparks & longer life Maintenance free Good weight/size to power ratio

DISADVANTAGES Higher cost Hall effect sensor might not work

properly Requires additional sensors Sudden change in load causes back emf

to become out of synchronous resulting loss of speed and torque

Must rotate at minimal speed to generate sufficient back emf for the drive to sense

APPLICATIONS LOW POWER BLDC HIGH POWER BLDC

1) Medical field a. Optimising power density

b. Heat transfer efficient c. medical analyser

d.sleep apnea treatment

2)Consumer electronics

1)Transport2)Heating & ventilation3)Radio controlled cars4)Industrial engg.

CONCLUSION Due to all those advantages BLDC is now

replacing the conventional DC motor & increasing popularity.

Various researches are going on for reducing its complexity in drive circuit with different types of sensors.

As sensor less BLDC drives continue to develop and costs are reduced, the attractiveness of BLDC motors will continue to increase.

THANK YOU