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 Motor
1. 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
A C Hybrid
E lectricMoto r
DC
Induct ion S ynchronous CompoundPermanent
MagnetS eriesS hunt
B rushlessDC
V ariableFrequency
S teppersS ync hronousPhase Loc ked
Loop
Po lyphase S ingle Phase
W oundRotor
S quirrel Cage S haded Po le Capacito r
C a p a c it o r St a r t
P e r m a n e n t Sp litC a p a c it 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 Swit c h in g
A C- DC S plit Field
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 r uc t io n
InverterDriven
Elec t ronicCommunic at ion
S ynchronous Induct ion
W o un d R o t o r
P e r m a n e n t M a gn 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
ReluctancePermanent
MagnetS mall A ngle
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