Multiphase Brushless DC MotorPresented By:

Talha Zahid 2014 EE 169 Zain Ul Abideen 2014 EE 172 Mohammad Rehan Majeed 2014 EE 180 Mohammad Shazil Majeed 2014 EE 181

Contents• Abstract • Classifications• Brushed DC Motors• Definition• Types of BLDC Motor• Brushless DC Motor• Working• 3 Phase Commutation• 5 Phase Commutation• Pros and Cons of Multiphase

BLDCMs• Trapezoidal and Sinusoidal

Constructions

Abstract• BLDCMs are motors which are powered by DC source

via an inverter which produces an electric signal to drivethe motor• High torque and low speed motor

Classification

• DC Motor Brushed Brushless

• Brushless (On the basis of Rotor) IN-RUNNER OUT-RUNNER

Brushed DC MotorContains Commutator and Brushes

Definition of Brushless DC Motor• Brushless motor is a high torque low speed DC motor which has a

rotor of permanent magnet and stator(armature) of electro-magnets. The poles of rotor are attracted or repelled by creating desired poles on the stator winding.• It is type of hybrid motors because it includes both AC & DC.• Flipped inside out the brushed motor

WHY BRUSHLESS???• More efficient• More reliable• Less Noisy• Lighter with same power

output• When we need long life

and reliable operation

Structure• Rotor

Permanent Magnet and Shaft

• Stator Armature

• Electronic Sensor Hall Effect Sensor

Optical Sensor

• DC To AC Inverter

Working • 3 Coil 2 Pole BLDC Motor

Analogy for Rotor Movement

Which coil to energize?When to energize?

Hall Effect Sensor Detects the position of the rotor

Commutation

DC to AC InvertersInverter for 3 Phase

Inverter for N Phase

5 Phase Commutation• Voltage difference of 2π/5• 5 phase 8 pole motor• 5 Hall Sensors• 10 Step Commutation

Increasing Rotor Poles• Size of permanent magnet• Rotor diameter• Torque Increases

Speed Control of BLDC MotorWe can control the speed of this motor by two methods1) No. of stator poles per phase2) Frequency

Speed Control of BLDC MotorWe can find the approx. speed of this motor by the following formula:

Control of BLDC Motor• The waveforms produced by inverters is of two types:1) Trapezoidal waveform2) Sinusoidal waveform

Trapezoidal Control• Motors powered by trapezoidal waveforms produce 10% more torque

then those powered by sinusoidal.• These motors are not much smooth and they have ripples in torque.

Sinusoidal Control• The sinusoidal control is used for low speed because it is smooth and

produces less ripple torque.

Back emf of BLDC Motor• We can also detect the rotor position by motor’s back emf instead of

sensors.• This method is only applicable for high speed motors so that there is

enough bemf amplitude.[2]• As the operating speed of motor increases, the frequency of bemf

also increases, so, the relative speed of switching remains contant.

Trapezoidal Back EMF• We integrate the trapezoidal bemf by controller and thus it can

control current waveform.• The use of sinusoidal wave is not feasible.

Pros of Multiphase BLDC Motor• Minimize torque ripple• Reduced Noise• Increased power density• Improves fault-tolerance w.r.t open circuit lags

3 phase torque

Multi phase torque

• High Efficiency• High Torque to Weight Ratio• Longer Life time• Compact And Lightweight• Better For Environment• Less Maintenance, High Reliability

Cons of Multiphase BLDCM• Complex inverter control scheme • High cost

ApplicationsTransport• Electric Vehicles• Hybrid Vehicles

ApplicationsComputer Applications• PC fans• DVD Players• Floppy Drive

ApplicationsHeating And Ventilation• HVAC And Refrigeration Industries

ApplicationsMotion Control Systems• Pumps• Fans• Positioning• Actuating

ApplicationsAeromodeling• Aircrafts• Helicopters• Best use of High Power to Weight Ratio

ApplicationsRadio Controlled Cars• Less Input Power• More Torque

References[1] Delmar's Standard Textbook of Electricity[2] Power Electronics Handbook: Devices, Circuits and Applications

QUESTIONS

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