Transcript ECE 364 - Power Electronics - CEME Logo Research Projects by Area

The Nature and Promise of 42 V
Automotive Power: An Update
Power Area and CEME Seminar, 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
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Why 42 V? Safety and other reasons.
Target power levels.
Architectures.
Points about engineering research needs.
Major applications: power steering,
starter-alternators, etc.
• “Mild hybrid” designs based on 42 V.
• Research opportunities.
• Conclusion.
Grainger Center for Electric Machines and Electromechanics
University of Illinois at Urbana-Champaign
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Why 42 V?
• The “electrification” of the automobile is a
major step in its evolution.
• Electrical applications are beneficial for the
same reasons as for systems in aircraft:
– Better efficiency
– More flexible control
– Ease of energy conversion
• Low-cost control and conversion of energy is
a key point.
• Electric power is rising because of electric
auxiliaries as well as more features.
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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.
• Performance is decoupled from the engine.
• Many estimates have been made, such as
10% fuel economy improvements by simple
electrification of existing functions.
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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 -ultimately the self-starting engine.
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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.
– The total electric load is about 1500 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?
• 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
• Industry premise: stay with an open electrical
system for the foreseeable future.
• This philosophy supports the option for
evolutionary change of automotive electric
power.
Grainger Center for Electric Machines and Electromechanics
University of Illinois at Urbana-Champaign
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Safety Issues
• There are also “fully regulated” and “battery
regulated” systems.
• Battery-regulated system ultimately defer to
the battery to set the voltage level.
• A battery-regulated system must allow for
– Polarity reversal
– Disconnection: momentary or continuous
– Wide voltage swings
• Inductive spikes from corrosion or deliberate
disconnect are significant.
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University of Illinois at Urbana-Champaign
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Safety Issues
• 12 V battery systems require undamaged
operation at –12 V or from short-term spikes
up to 75 V.
• At higher battery voltages, surge suppressors
and other add-ons will be needed to limit
these extremes to present levels.
• In a battery regulated system, 36 V is about
the highest possible level (but these are
charged at 42 V) without excessive possibility
of damage and spikes much beyond 60 V.
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University of Illinois at Urbana-Champaign
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Safety Issues
• In a fully regulated system, there is some
buffering between the battery and the rest of
the system.
• With full regulation, the wide swings of a
battery system are not necessarily
encountered by the user.
• 48 V batteries are possible within the 60 V
limit, with such regulation.
• The higher voltages also support extra efforts,
such as anti-reversing diodes.
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University of Illinois at Urbana-Champaign
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Safety Issues
• The term “42 V” refers to a range of choices
with nominal battery levels in the range of
36 V to 48 V.
• While there is incomplete consensus, the
evolutionary approach would favor 36 V
batteries (charging at 42 V).
• For comparison, we should take 42 V to
mean a tripling of present voltage, to give at
least triple the power.
• With better generation, power up to 5x is
available.
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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
• At 42 V, a car’s electrical system rivals that of
a house.
• But, 10 kW is not enough for traction power.
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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 or less 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 (but
they are disappearing).
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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.
– What about fuses? No central point is available.
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University of Illinois at Urbana-Champaign
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Architectures
• Costs would seem to dictate a single-battery
arrangement.
• However, this involves either a high-power
42V to 12V converter (bidirectional) or a
troublesome 42 V battery.
• Some researchers talk about a small dc-dc
converter just for jump starts.
• 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.
• Fusing.
• Arcs: much above 12 V, it becomes possible
to sustain an arc in close quarters.
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University of Illinois at Urbana-Champaign
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Connectors
• 150 A connector for 42 V (AMP, Inc.
prototype).
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University of Illinois at Urbana-Champaign
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Points About Research Needs
• Many of the new challenges of 42 V have
been addressed in other contexts:
– 48 V systems throughout the telephone network
(with battery regulation)
– Higher dc voltages in several aerospace
applications (with bigger arcing problems in lowpressure ambients)
• Methods need to be adapted to the low-cost
high-vibration automotive case.
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University of Illinois at Urbana-Champaign
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Points About Research Needs
• Motors are of keen interest.
– Dc motors are cheap to build because of the
convenient wound-rotor structure.
– The small machine design methods for cars do not
translate well to 42 V.
• At 42 V, ac motors make sense.
• But – small ac motors have been expensive
in most contexts.
• How to build cheap, small ac motors (with
electronic controls)?
Grainger Center for Electric Machines and Electromechanics
University of Illinois at Urbana-Champaign
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Points About Research Needs
• Fusing is critical.
• Power semiconductor circuits capable of
acting as “self fuses” – active devices used as
circuit breakers based on local sensing.
• Actual fuses and circuit breakers with costeffective arc management suitable for
automotive environments.
• Fusing issues (among others) have slowed
down the development of 42 V systems.
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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.
• 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.
• Both permanent magnet and
induction types are being
studied.
Source: Mechanical Engineering
Magazine online, April 2002.
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University of Illinois at Urbana-Champaign
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Major Applications
• Provides on-demand starts.
• Supports regenerative braking.
• The very fast dynamics of an ac machine
allows even active torque ripple cancellation.
• If ripple can be cancelled, there is promise for
much quieter engines and much lower
vibration levels.
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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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Major Applications
• Active suspensions.
• Use electromechanical actuators in
conjunction with mechanical suspension
members.
• With enough actuator power, road bumps
(large and small) can be cancelled with an
active suspension.
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University of Illinois at Urbana-Champaign
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Major Applications
• Catalyst management systems and exhaust
treatment.
• Today, most automotive emissions occur in
the first few minutes of operation, when the
catalyst is too cold to be effective.
• Catalyst heaters or short-term exhaust
management systems can drastically reduce
tailpipe emissions in modern cars and trucks.
• Electrostatic precipitator methods can be of
value with diesel particulate exhaust.
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University of Illinois at Urbana-Champaign
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Additional Applications
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University of Illinois at Urbana-Champaign
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Mild Hybrids
• The key limitation of 42 V is that it really does
not support electric traction power levels.
• As the promise of electric and hybrid vehicles
becomes clearer, engineers push for higher
power levels – beyond the reach of 42 V.
• A compromise is possible: the “mild hybrid”
vehicle.
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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
can provide a useful level of “traction” power.
• The technique is accessible in a 42 V system,
although higher voltage (144 V in the Insight)
is beneficial.
• A 42 V ISA has substantial promise for fuel
economy improvements, and straddles the
boundary between a conventional car with an
ISA and a mild hybrid.
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University of Illinois at Urbana-Champaign
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Other Hybrids
• Higher-power hybrids require high voltage
(240 V and up) for traction power.
• Electrical accessories are essential.
• Such cars can benefit from 42 V systems.
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University of Illinois at Urbana-Champaign
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Other Hybrids
Source: www.familycar.com
• The Toyota hybrid
system operates at
288 V, and reaches
30 kW.
• All key
accessories are
electric.
Grainger Center for Electric Machines and Electromechanics
University of Illinois at Urbana-Champaign
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Research Opportunities
• Low-cost small ac motor systems:
– 42 V dc bus
– Cheap inverters
– Small ac motors that can be manufactured easily
• Engine electromechanical devices and
controls.
• Protection and semiconductor “fusing.”
• System-level analysis.
Grainger Center for Electric Machines and Electromechanics
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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The End!
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University of Illinois at Urbana-Champaign
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Why Not Just Big Batteries?
• Lead-acid battery energy density is only
about 1% of that in gasoline.
• Our test car: 600 lb battery pack 
equivalent to one gallon of gas!
Grainger Center for Electric Machines and Electromechanics
University of Illinois at Urbana-Champaign
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Electric and Hybrid Gallery
• General Motors EV1.
• 1300 lb battery pack at
312 V, 102 kW motor.
• 0-60 mph in less than 9 s.
• Volvo turbine-based
hybrid prototype.
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University of Illinois at Urbana-Champaign
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Electric and Hybrid Car Gallery
• This Ford Escort was the first “true practical”
prototype hybrid – a complete station wagon.
• Second-gen
diesel hybrid.
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University of Illinois at Urbana-Champaign
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Electric and Hybrid Car Gallery
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University of Illinois at Urbana-Champaign
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Toyota Hybrid Specs
• Small NiMH battery set, 288 V.
• 40 HP motor, ac permanent magnet type.
• Continuously-variable transmission with sunplanet gear set for energy control.
• 0-60 mph in about 17 s.
• 1500 cc engine can hold 75 mph indefinitely.
• Atkinson cycle engine (“5-stroke”) gets better
thermal efficiency but lower output torque.
• Rated 54 mpg city, 48 highway.
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University of Illinois at Urbana-Champaign
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Electric and Hybrid Car Gallery
• Toyota architecture 
• Honda architecture:
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University of Illinois at Urbana-Champaign
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