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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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the nature and promise of 42 v automotive power an update

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
Outline
  • 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.
why 42 v
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.
why 42 v1
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.
why 42 v2
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.
why 42 v3
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.
why 42 v4
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.
safety issues
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.
safety issues1
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.
safety issues2
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.
safety issues3
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.
safety issues4
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.
safety issues5
Safety Issues
  • The term “42 V” refers to a range of choices with nominal battery levels in the range of36 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.
safety issues6
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.
power levels
Power Levels
  • At 42 V, a car’s electrical system rivals that of a house.
  • But, 10 kW is not enough for traction power.
architectures
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 tractionpower.
  • Incandescent lamps, for example, are more rugged and more reliable at low voltages (but they are disappearing).
architectures1
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.
architectures2

42V

BATTERY

ENGINE

42V

ALTERNATOR

42V

LOADS

DC–DC

12V LOADS

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

www.hoppecke.com

architectures3

42V

BATTERY

ENGINE

42V

ALTERNATOR

42V

LOADS

BIDIRECTIONAL

DC–DC

12V

BATTERY

12V LOADS

Architectures
  • Dual battery:
  • The dc-dc converter mustbe bidirectional to supportstarting and reliability.
architectures4

REGULATOR

ENGINE

42V

STARTER/

ALTERNATOR

42V

LOADS

BIDIRECTIONAL

DC–DC

12V

BATTERY

12V LOADS

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

Source: Mechanical Engineering Magazineonline, April 2002.

architectures5

42V

BATTERY

ENGINE

42V

STARTER/

ALTERNATOR

42V

LOADS

LOCAL

DC/DC

LOADS

Architectures
  • Distributed converters with 42 V battery.
  • Here there are many dc-dcconverters at the variousloads.
architectures6
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.
architectures7
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).
issues
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.
connectors
Connectors
  • 150 A connector for 42 V (AMP, Inc. prototype).
points about research needs
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 low-pressure ambients)
  • Methods need to be adapted to the low-cost high-vibration automotive case.
points about research needs1
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)?
points about research needs2
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 cost-effective arc management suitable for automotive environments.
  • Fusing issues (among others) have slowed down the development of 42 V systems.
major applications
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.

major applications1
Major Applications
  • Electric air conditioning.
  • Remove the air conditioningsystem from engine belt drive.
  • Provides much better controland flexibility.
  • Easier cycling,possibleheat pump application.
major applications2
Major Applications
  • Integrated starter-alternator (ISA).
  • Build an electric machine intoor around the flywheel.
  • Both permanent magnet andinduction types are beingstudied.

Source: Mechanical EngineeringMagazine online, April 2002.

major applications3
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.
major applications4
Major Applications
  • Electromechanical engine controls.
  • Valves.
  • Fuel.

Source: FEV Engine Technology, Inc.

major applications5
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.
major applications6
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.
mild hybrids
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.
mild hybrids1
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 an“all-electric” regime.
  • The Honda Insight is a good example.

Source: www.familycar.com

mild hybrids2
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.
other hybrids
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.
other hybrids1
All key accessories are electric.

The Toyota hybrid system operates at 288 V, and reaches 30 kW.

Other Hybrids

Source: www.familycar.com

research opportunities
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.
conclusion
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.
why not just big batteries
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!
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.

Electric and Hybrid Gallery
electric and hybrid car gallery
Electric and Hybrid Car Gallery
  • This Ford Escort was the first “true practical” prototype hybrid – a complete station wagon.
  • Second-gendiesel hybrid.
toyota hybrid specs
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.
electric and hybrid car gallery2
Electric and Hybrid Car Gallery
  • Toyota architecture 
  • Honda architecture:
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