Transcript ECE 364 - Power Electronics

Power Electronics and 42 V
Automotive Power
US-Jordan Workshop, December 2002
P. T. Krein
Grainger Center for Electric Machinery and Electromechanics
Department of Electrical and Computer Engineering
University of Illinois at Urbana-Champaign
Outline
• The growth of automotive power
electronics.
• Why 42 V? Power levels, accessories,
safety, and other reasons.
• Single and two-battery architectures.
• Multiplexed power.
• Major applications: power steering,
starter-alternators, etc.
• “Mild hybrid” designs based on 42 V.
• Conclusion.
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University of Illinois at Urbana-Champaign
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The Growth of Auto Power Electronics
• Power electronics for transportation is a
major growth area.
– Management of 12 V power
– Audio systems
– Motor controls
• The move to higher voltages extends the
reach in many ways.
• The ultimate application is electric traction
(but it is not really the most important!).
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University of Illinois at Urbana-Champaign
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Why 42 V?
• When electricity is used to power various
components (steering, brakes, suspension,
air conditioning), the results are better
efficiency and more flexible performance.
• Many estimates have been made, such as
10% fuel economy improvements just be
using a higher voltage.
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University of Illinois at Urbana-Champaign
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Why 42 V?
• Possible new features:
– Combined starter-alternator to reduce costs and
enhance performance.
– Regenerative braking.
– “Start on demand” arrangements to avoid idle
engines.
– Improved, more efficient power steering and other
subsystems.
– Active suspensions.
– Electrical valves and engine elements.
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University of Illinois at Urbana-Champaign
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Why 42 V?
• The conventional car is rapidly becoming
more electric.
– A new car can contain up to 100 motors.
– The total electric load is about 1000 W today, and
is increasing toward 5000 W.
– Conventional alternators cannot deliver more than
about 2000 W, and are not efficient.
– A higher voltage system supports lower current
and loss.
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University of Illinois at Urbana-Champaign
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Why 42 V?
Car motor usage is growing fast.
It will soon rise to 200 electric motors per car.
Source: Johnson Electric, 1999.
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University of Illinois at Urbana-Champaign
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Why 42 V?
• Three alternatives:
– Stick with 12 V. This limits effective power levels.
– Get the voltage as high as possible (>100 V). This
requires a major overhaul of safety systems and
basic designs.
– Push the voltage as high as possible before
significant safety issues come into play.
• 42 V tries to do the last: get the voltage as
high as possible while avoiding severe safety
issues.
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University of Illinois at Urbana-Champaign
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Safety Issues
• A car’s electrical system is typically “open.”
• Complicated wiring harnesses with close
contact and hundreds of connections.
• Regulatory agencies have set a level of about
60 V dc as the maximum reasonable level in
an “open” system.
• Headroom is required to stay below this level
under all allowed conditions.
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University of Illinois at Urbana-Champaign
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Safety Issues
• When there is no special electrical regulation,
36 V batteries are the maximum.
• In a fully regulated system, 48 V batteries are
possible within the 60 V limit.
• The term “42 V” refers to a range of choices
with nominal battery levels in the range of
36 V to 48 V.
• For comparison, we should take 42 V to
mean a tripling of voltage, to give about triple
the power.
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University of Illinois at Urbana-Champaign
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Safety Issues
• We can also consider a “closed system,” in
which electrical contact is more protected.
• Closed systems are used in today’s hybrid
and electric cars.
• The voltage levels there can exceed 300 V
dc.
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University of Illinois at Urbana-Champaign
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Power Levels
Voltage
Typical
power level
Maximum
power level
12 V
1200 W
2000 W
42 V
5000 W
10 kW
300 V
30 kW
100 kW
• A car’s electrical system rivals that of a
house.
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University of Illinois at Urbana-Champaign
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Architectures
• Each automotive voltage level has
advantages for some loads.
• 12 V for lamps, sensors, electronics,
controls.
• 42 V for motors, pumps, and fans.
• High voltage for electric traction
power.
• Incandescent lamps, for example, are more
rugged and more reliable at low voltages.
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University of Illinois at Urbana-Champaign
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Architectures
• Many possible architectures are possible.
• Most retain some 12 V capacity.
• They are typically divided into single-battery
and dual-battery systems.
• There is no consensus on which to select,
and we are likely to see several.
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University of Illinois at Urbana-Champaign
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Architectures
• Single battery at 42 V:
ENGINE
42V
BATTERY
42V
LOADS
42V
ALTERNATOR
• Problem: jump starts?
• Problem: charge balance.
DC–DC
12V LOADS
www.hoppecke.com
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University of Illinois at Urbana-Champaign
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Architectures
• Dual battery:
ENGINE
42V
BATTERY
42V
LOADS
42V
ALTERNATOR
• The dc-dc converter must
be bidirectional to support
starting and reliability.
BIDIRECTIONAL
DC–DC
12V
BATTERY
12V LOADS
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University of Illinois at Urbana-Champaign
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Architectures
• 12 V battery
ENGINE
REGULATOR
42V
STARTER/
ALTERNATOR
• Here a starter-alternator
is shown as well.
42V
LOADS
BIDIRECTIONAL
DC–DC
12V
BATTERY
12V LOADS
Source: Mechanical
Engineering Magazine
online, April 2002.
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University of Illinois at Urbana-Champaign
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Architectures
• Distributed converters with 42 V battery.
ENGINE
42V
BATTERY
42V
STARTER/
ALTERNATOR
42V
LOADS
• Here there are many dc-dc
converters at the various
loads.
LOCAL
DC/DC
LOADS
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University of Illinois at Urbana-Champaign
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Architectures
• The ultimate is a true multiplexed system:
– Deliver a single 42 V power bus throughout the
vehicle, with a network protocol overlaid on it.
– Local dc-dc converters provide complete local
operation and protection.
– A ring bus or redundant bus structure could be
used to enhance reliability.
– Fuse coordination is important.
• Most systems are partially multiplexed (power
and network distribution rather than individual
loads).
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University of Illinois at Urbana-Champaign
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Issues
• “Key off” loads: sensors, alarms, clocks,
remote systems. All draw down power.
• “Flat” loads draw roughly fixed power,
although the alternator
output can vary.
• Connectors, 150 A 
• Fusing.
• Arcs: much above 12 V,
it becomes possible to
sustain an arc.
Source: Amp, Inc.
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University of Illinois at Urbana-Champaign
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Major Applications
• Electric power steering.
• Two forms: assist pump and direct electric.
• The assist pump uses an electric motor to
drive a conventional hydraulic unit.
• The direct system
uses electric motors with
the steering rack.
• In both cases, action can
be controlled independent
of the engine.
Source: Delphi Corp., Saginaw Steering Systems Div.
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University of Illinois at Urbana-Champaign
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Major Applications
• Electric air conditioning
or heat pumps.
• Remove the air conditioning
system from engine belt drive.
• Provides much better control
and flexibility.
• Easier cycling,possible
heat pump application.
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University of Illinois at Urbana-Champaign
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Major Applications
• Integrated starter-alternator (ISA).
• Build an electric machine into
or around the flywheel.
• Provides on-demand starts.
• Supports regenerative braking.
• One prototype was even used
to cancel engine torque
pulsations with active motor
control.
Source: Mechanical Engineering
Magazine online, April 2002.
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University of Illinois at Urbana-Champaign
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Major Applications
• Electromechanical engine controls.
• Valves.
Source: FEV Engine Technology, Inc.
• Fuel.
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University of Illinois at Urbana-Champaign
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Mild Hybrids
• A “light” hybrid or “mild” hybrid uses a small
motor to manage
performance.
• The engine can be
shut down at stops.
• Braking energy
can be recovered.
Source: www.familycar.com
• The car does not operate in an
“all-electric” regime.
• The Honda Insight is a good example.
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University of Illinois at Urbana-Champaign
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Mild Hybrids
• For a mild hybrid approach, about 5 kW or so
is the minimum “traction” power.
• The technique is accessible in a 42 V system,
although higher voltage (144 V in the Insight)
is beneficial.
• One hesitation for 42 V is the marginal ability
to support traction power and hybrid designs.
• A 42 V ISA has substantial promise for fuel
economy improvements.
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University of Illinois at Urbana-Champaign
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Key Power Electronics Needs
•
•
•
•
•
Low-cost dc-dc converters.
High-power bidirectional dc-dc converters.
Low-cost 42 V inverters for small ac drives.
Small ac motor designs, 100 W and below.
“Semiconductor fuse” automatic protection
circuits.
• Improved battery and system management.
• High momentary power drivers for engine
electromechanics.
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University of Illinois at Urbana-Champaign
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Conclusion
• The continuing increase in electric power
levels in automobiles will require higher
voltages.
• 42 V systems (batteries at 36 V or 48 V) are
the highest possible in an “open” electrical
system.
• There are fuel economy improvements just at
this level, but the extension to “mild hybrids”
offers much more.
• While the industry is now is a “go slow” mode
for 42 V, no one doubts its eventual use.
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University of Illinois at Urbana-Champaign
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