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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: