Brushless DC Motors

Sohaib Hasan

Motor Basics• What is a motor

– Converts electrical energy into kinetic energy

• Where did it come from– Identification of rotating magnetic field principle

by Nicola Tesla in 1882– Introduction of Electric Motor by Nicola Tesla in

December 1889 (U.S. Patent 0416194)

Parts of a Motor1. End Bell Fastners2. Shaft Key & Keyways3. Bearing & Brushings4. End Ball Flanges5. Identification Plates6. Wire Warnish7. Commutators8. Brush Holders9. Laminations10. Conduit Connection Box11. Magnets (Ferrites)

Brushless Motor Components

Brush Type Motor Components Images courtesy of Hernon Adhesives & Sealents (http://www.hernonmfg.com/electricmotor.htm)

Parts of a Motor

Images courtesy of How Stuff Works(http://electronics.howstuffworks.com/motor3.htm)

How It Works• When electric current passes

through a coil in a magnetic field, the magnetic force produces a torque which turns the motor.

• Force in Motor:F=ILBF = Force B = Magnetic FieldL = Length of ConductorI = Current in Conductor

• Torque in Motor:T = IBA sin θA = LWL = Length of WindingW = Width of Winding

Images courtesy of Wikipedia(http://en.wikipedia.org/wiki/Electric_motor)

Motor Types

AC Hybrid

E lectr icMo to r

DC

Induct ion S ynchrono us Compound PermanentMagnetS eriesS hunt Brush less

DCV ariable

Frequency S teppersS ync hronousPhase Loc ked

Loop

Po lyphas e S ingle Phas e

W oundRoto r S quirrel Cage S haded Po le Capacito r

C a p a c i t o r St a r t

P e rm a n e n t Sp l itC a p a c i t o r

T wo C a p a c it o r

S ingle /Po lyphase

W o un d F ie ld

P e r m a n e n t M a gn e t

R e luc t a n c e

H y st e r e sis

M ult ip le Sp e e dP o le Sw it c h in g

AC- DC S plit F ield

M o v in g C o il

B a sk e t W e a v e

D C T o rq u e r

C o n v e n t io n a lC o n st ruc t io n

InverterD riven

Elec t ronicCommunic at ion S ynchrono us Induction

W o un d R o t o r

P e rm a n e n t M a g n e t

St a t o r C o n t r o l

R o t o r C o n t r o l

Reluctance PermanentMagnet S mall Angle

R e luc t a n c e

P e r m a n e n tM a gn e t

Brushless DC Motor

• No Commutators

• Position of Coils with respect to the magnetic field is sensed electronically.

• Current is commutated through electronic switches to appropriate phases.

How it Works

• Halls 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

Images courtesy of Servo Magnetics(http://www.servomag.com/flash/2-pole/2pole-bldc-motor.html)

Advantages• Increased Reliablilty & Efficiency

• Longer Life

• Elimination of Sparks from Commutator

• Reduced Friction

• Faster Rate of Voltage & Current

• Precision Voltage & Current Applied to Field Coils

Applications• Low Power

– Consumer Electronics– Medical Field

• High Power– Industrial Machinery– Vehicles – Airplanes

Disadvantages• Requires Complex Drive Circuitry

• Requires additional Sensors

• Higher Cost

• Some designs require manual labor (Hand wound Stator Coils)

Useful Links• http://en.wikipedia.org/wiki/Electric_motor

• http://electronics.howstuffworks.com/motor3.htm

• http://www.hernonmfg.com/electricmotor.htm

• http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

• http://www.servomag.com/flash/2-pole/2pole-bldc-motor.html

• http://www.engineersedge.com/motors/brushless_dc_motor.htm

• http://www.freescale.com/webapp/sps/site/application.jsp?nodeId=02nQXGrrlPY7r803B5