Transcript Background Lecture - IEEE Real World Engineering Projects

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Brushless DC Motor
Background Lecture
What is a motor?
A motor converts electric energy to rotating mechanical energy.
Electric Energy
Input
voltage and current
Energy
Converter
typical:
magnetic field
Rotating Mechanical
Energy Output
speed and torque
What are motors used for?
What are motors used for?
Rotating action moves
loads
• Material-movers
– Fans, pumps,
conveyors, robots
• People-movers
– Elevators, escalators,
moving walkways
– Hybrid cars, buses,
electric motorcycles,
personal transporters
(Segway)
What are motors used for?
Rotating action moves
loads
• Material-movers
– Fans, pumps,
conveyors, robots
• People-movers
– Elevators, escalators,
moving walkways
– Hybrid cars, buses,
electric motorcycles,
personal transporters
(Segway)
Personal Electric Vehicles
New Transportation Alternative
•
•
•
•
Single passenger
1-10km trips
Open to weather
Less-than-highway speeds
up to 50km/hr
• Purchase cost US$2000 up
to US$100,000
PEVs Potential Impact on Society
• Reduced greenhouse gas emission versus
cars
• Higher fuel efficiency versus cars
How much CO2 comes from one gallon
(6.3lbs) of automobile gasoline?
• When gasoline burns, the carbon
and hydrogen separate.
• The hydrogen combines with oxygen
to form water (H2O), and carbon
combines with oxygen to form
carbon dioxide (CO2).
• A carbon atom has a weight of 12,
and each oxygen atom has a weight
of 16, giving each single molecule of
CO2 an atomic weight of 44 (12 from
carbon and 32 from oxygen).
How much CO2 comes from one gallon
(6.3lbs) of automobile gasoline?
• To calculate the amount of CO2
produced from a gallon of gasoline, the
weight of the carbon in the gasoline is
multiplied by 44/12 or 3.7
• Since gasoline is about 87% carbon and
13% hydrogen by weight, the carbon in a
gallon of gasoline weighs 5.5 pounds (6.3
lbs. x .87).
• Multiply the weight of the carbon (5.5
pounds) by 3.7, which equals
20 pounds of CO2!
Since PEVs are electric, do they
produce CO2?
• Not directly. The CO2
produced by electric
power plants must be
accounted for.
• For the 2004 fuel mix
of US electricity
production, the
average CO2
produced is
1.55 lbs CO2 per kWh
What is CO2 production per
passenger mile?
• If an automobile gets 20 miles/gallon, then
calculate the CO2 produced per gallon.
• You will further explore this question in the
assignment
Barriers to PEV Adoption
• New technology
• Battery energy density and acquisition
cost
– Recent advances driven by cell phone market
• Production economies
• Local traffic laws
• Weather inconvenience
PEV Advantages Over Cars
• Significantly higher fuel efficiency on a perpassenger mile basis
• Significantly reduced greenhouse gas
emission
• Reduced congestion in high density urban
areas
– London, Manhattan per car entry fee
• Shorter trip times in high density urban areas
• Quieter
Does anyone have a motor with them?
What is it used for?
Can we see it?
Does it operate from a dc or ac power
source?
Motor names
• (Brushed) DC motors
• Brushless DC motors
• AC motors
– Induction motors
– Synchronous motors
(generators)
Types of voltage inputs
• DC (direct current)
– Voltage does not vary with time
• AC (alternating current)
– Voltage changes varies over time
– Typically a sinusoid, but maybe not
How do motors work?
One explanation:
Electric current interacts with magnetic field
to produce torque on a shaft
Another:
Two magnetic fields interact to produce
torque on a shaft
How does a (brushed) DC motor work?
(Brushed) DC Motor from RC Car
How does a brushless DC motor work?
N
Switch state:
If magnet near coil, ON
Else OFF
Why doesn’t rotor stop
when coil is off?
BLDC you will build
The components of an Aveox 36/30/1.5 brushless motor.
How does the switch know if
there is a magnet nearby?
• Use a switch that detects a magnetic field
Magnetic reed switch
• Use a sensor that detects a magnetic field
and commands another switch
Hall-effect sensor and transistor
• Use a sensor that optically detects the rotor
position and commands another switch
Optical encoder and transistor
How does the switch know if
there is a magnet nearby?
• Use a switch that detects a magnetic field
Magnetic reed switch
• Use a sensor that detects a magnetic field
and commands another switch
Hall-effect sensor and transistor
• Use a sensor that optically detects the rotor
position and commands another switch
Optical encoder and transistor
How does the switch know if
there is a magnet nearby?
• Use a switch that detects a magnetic field
Magnetic reed switch
• Use a sensor that detects a magnetic field
and commands another switch
Hall-effect sensor and transistor
• Use a sensor that optically detects the rotor
position and commands another switch
Optical encoder and transistor
Reed Switch BLDC Schematic
1.5V
1.5V
COIL
l
co i
ed h
re itc
sw
N
1.5V
Reed
switch
1.5V
Reed Switch Technology
Typical rating:
sw
8
10
failure
MTBF: mean time
between failure
How long will a typical reed switch last continuously operating a
four pole rotor BLDC at 1000rpm?
Reed Switch Technology
Typical rating:
sw
8
10
failure
How long will a typical reed switch last continuously operating a
four pole rotor BLDC at 1000rpm?
rev  sw 

3 sw
1000
4

4

10

 rev 
min
min



 8 sw  min 
3 min
 10 failure  4  103 sw   25  10 failure



(416 hours or 1.14 years)
What if we want to continuously
operate for more than one year?
ed h
re itc
sw
N
l
co i
1.5V
COIL
1.5V
1.5V
Reed
switch
1.5V
What if we want to continuously
operate for more than one year?
Solution:
replace the reed switch with a transistor
Typical transistor MTBF is >100,000’s hours
(e.g., 200,000 hours or 23 years)
TIP106
What are the terminals on a
transistor?
emitter
base
collector
The switch is between emitter and collector.
The base controls the state of the switch.
Use transistor as a switch
1.5V
COIL
N
1.5V
co i
l
1.5V
1.5V
TIP106
base
What’s missing?
Add magnetic sensor to command
transistor to switch
Hall-effect sensor
X
3121E
Where are Hall-effect sensors used
(besides) BLDCs?
Add magnetic sensor to command
transistor to switch
Hall-effect sensor
X
3121E
Where are Hall-effect sensors used
(besides) BLDCs?
Speedometers on bicycles.
Why not build this circuit?
1.5V
COIL
Coil resistance about 4 ohms.
1.5V
1.5V
1.5V
X
3121E
Why not build this circuit?
COIL
1.5V
1.5V
1.5V
1.5V
X
3121E
Coil resistance about 4 ohms.
coil current 
V 6
  1.5A
R 4
Power Transistor Amplifies
COIL
1.5V
1.5V
10 kW
Coil circuit switched by
power transistor with Hall
effect sensor
1.5V
TIP106
1.5V
X
3121E
Precision BLDC using optical
encoder
Optical Switch
What should be the
angle between one
encoder tab and a
rotor magnet?
Optek OPB870
Optical Encoder BLDC Schematic
COIL
1.5V
1.5V
10 kW
Coil circuit switched by
power transistor with
slotted optical sensor
270 W
1.5V
TIP106
1.5V
OPB800
Optical switch
How does a BLDC motor make a
difference in PEV’s?
• Higher power to weight ratio
– BLDC: 2000 W/kg
– Brushed DC: 1000 W/kg
• Higher efficiency in converting electric energy to rotating
mechanical energy
– BLDC: >90%
– Brushed DC: 75%
• Lower maintenance
– BLDC: no regular maintenance
– Brushed DC: replace brushes
• Lower gear-ratio transmission
– BLDC: 5:1@2500rpm, typically single-stage
– Brushed DC: 20:1 @10,000rpm, typically two-stage
Drawbacks to BLDC versus
Brushed DC
• Higher acquisition cost
– BLDC with electronic controller about 50%
higher for 1.5hp
• High magnetic field strength permanent
magnets on rotor
Your assignment
• Build your own BLDC
• Read articles:
– Ulrich, “Estimating the Technology Frontier for
Personal Electric Vehicles”
– Heinzmann and Taylor, “The Role of the Segway
Personal Transporter in Emissions Reduction and
Energy Efficiency”
• Discover the potential impact of PEVs on
greenhouse gas emissions and fuel usage
• Write a 2-3 page report on your BLDC and
your discoveries