30-04-2011, 11:22 AM
PRESENTED BY:-
Diptirekha Sahoo
final.pptx (Size: 2.12 MB / Downloads: 293)
BRUSHLESS DC MOTOR PRINCIPLE AND APPLICATION
INTRODUCTION
T.G Wilson & P.H Tricky made a dc machine with solid state commutation (1962)
BLDC is also called ECMs
No need of commutator & brushes
Not directly operate from a dc voltage source
Combination of synchronous motor & a frequency inverter
WHY BLDC?
Limitations of conventional dc motor
Brushes may get displaced with increasing in speed
Difficulty in maintaining contact
Brushes & commutator requires maintanance
Limitation of synchronous motor
Speed can’t be varied
Problems with instability at any speed
WHY BLDC(contd.)
PRINCIPLE OF BLDC MOTOR
Frequency inverter used as commutator
Commutation depends on rotor position
Speed control by motor voltage
Angle between mmfs of stator & rotor is fixed to 90 deg (el.)
Motor behaves like a dc motor
No commutation occurs on the spinning shaft
THEORY OF OPERATION
Mode of Electronic commutation
(i)Sensor based(use of hall sensor)
- hall sensors are placed at every 120 deg.
- hall sensors sense the position of coil
6 commutation (phase) can be possible
The decoder circuit turns appropriate swithes on & off
The voltage through specific coil turns the motor
(i)Sensorless (use of MCUs)
- MCU measures back emf which determines the position of magnet & rot
THEORY OF OPERATION(Contd.)
How it Works
CONSTRUCTION OF BLDC
Shape is either cylindrical or pancake
Cylindrical BLDC(direction of magnetic flux is radial wrt rotational axis)
Inrunner(rotor inside)
Ex: hard disk drives
(ii) outrunner(rotor outside)
Ex: BLDC fan motors outrunner inrunner
CONSTRUCTION(contd.)
Pancake BLDC(direction of magnetic flux is parallel wrt axis of rotation)
(i)Single stator(lower torque)
Ex: floppy disk drive motors
(ii)Double stator(high torque) single stator double stator
Brushless pancake motor
ADVANTAGES OF BLDC
No brushes or commutators to wear out
no generation of EMI
High torque to inertia ratio
No windings on the rotor but supported by housing
High efficiency(up to 97%)
High heat transfer efficiency
No sparks & longer life
Maintenance free
Good weight/size to power ratio
DISADVANTAGES OF BLDC
Higher cost
Must rotate at minimal speed to generate sufficient back emf for the drive to sense
Sudden changes in load causes back emf to become out of synchronous resulting loss of speed & torque
Hall effect sensors might not work properly
Requires additional sensors
Requires complex drive circuitary
APPLICATION OF BLDC
Low power BLDC
(i)Consumer electronics
(ii)Medical field
(a)sleep apnea treatment
(b) Optimising power
density
©Heat transfer efficient
(d)Medical analyser
APPLICATION
High power BLDC
(i)Transport
(ii)Heating & ventilation
(iii)Model 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 brushless DC drives continue to develop and costs are reduced, the attractiveness of brushless DC motors will continue to increase.