Power Electronics and 42 V Automotive Power

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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

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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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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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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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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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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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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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Why 42 V?

• Three alternatives
• Stick with 12 V. This limits effective power
  levels.
• Get the voltage as high as possible (gt100 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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Safety Issues

• A cars 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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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 of36 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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Safety Issues

• We can also consider a closed system, in which
  electrical contact is more protected.
• Closed systems are used in todays hybrid and
  electric cars.
• The voltage levels there can exceed 300 V dc.

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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 cars electrical system rivals that of a house.

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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 tractionpower.
• Incandescent lamps, for example, are more rugged
  and more reliable at low voltages.

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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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Architectures

• Single battery at 42 V
• Problem jump starts?
• Problem charge balance.

www.hoppecke.com
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Architectures

• Dual battery
• The dc-dc converter mustbe bidirectional to
  supportstarting and reliability.

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Architectures

• 12 V battery
• Here a starter-alternatoris shown as well.

Source Mechanical Engineering Magazineonline,
April 2002.
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Architectures

• Distributed converters with 42 V battery.
• Here there are many dc-dcconverters at the
  variousloads.

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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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Issues

• Key off loads sensors, alarms, clocks, remote
  systems. All draw down power.
• Flat loads draw roughly fixed power, although
  the alternatoroutput can vary.
• Connectors, 150 A ?
• Fusing.
• Arcs much above 12 V,it becomes possible
  tosustain an arc.

Source Amp, Inc.
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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 systemuses electric motors withthe
  steering rack.
• In both cases, action canbe controlled
  independentof the engine.

Source Delphi Corp., Saginaw Steering Systems
Div.
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Major Applications

• Electric air conditioningor heat pumps.
• Remove the air conditioningsystem from engine
  belt drive.
• Provides much better controland flexibility.
• Easier cycling,possibleheat pump application.

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Major Applications

• Integrated starter-alternator (ISA).
• Build an electric machine intoor around the
  flywheel.
• Provides on-demand starts.
• Supports regenerative braking.
• One prototype was even usedto cancel engine
  torquepulsations with active motorcontrol.

Source Mechanical EngineeringMagazine online,
April 2002.
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Major Applications

• Electromechanical engine controls.
• Valves.
• Fuel.

Source FEV Engine Technology, Inc.
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Mild Hybrids

• A light hybrid or mild hybrid uses a small
  motor to manageperformance.
• The engine can beshut down at stops.
• Braking energycan be recovered.
• The car does not operate in anall-electric
  regime.
• The Honda Insight is a good example.

Source www.familycar.com
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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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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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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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The End
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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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Other Hybrids

• The Toyota Prius hybrid uses a 288 V battery
  system, and has a 30 kW motor.

Source www.familycar.com

• The major components are all electric.

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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!

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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-basedhybrid prototype.

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Electric and Hybrid Car Gallery

• This Ford Escort was the first true practical
  prototype hybrid a complete station wagon.
• Second-gendiesel hybrid.

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Electric and Hybrid Car Gallery
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Toyota Hybrid Specs

• Small NiMH battery set, 288 V.
• 40 HP motor, ac permanent magnet type.
• Continuously-variable transmission with
  sun-planet 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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Electric and Hybrid Car Gallery

• Toyota architecture ?
• Honda architecture