Why 42V bus 09 07 2013

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The Nature and Promise of 42 V

Automotive Power: An Update

P. T. Krein

Grainger Center for Electric Machinery and Electromechanics

Department of Electrical and Computer Engineering

University of Illinois at Urbana-Champaign

Power Area and CEME Seminar, December 2002

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Grainger Center for Electric Machines and Electromechanics University of Illinois at Urbana-Champaign

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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.

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Why 42 V?

• The “electrification” of the automobile is amajor step in its evolution.

• Electrical applications are beneficial for thesame 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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Why 42 V?

• Possible new features: – Combined starter-alternator to reduce costs and

enhance performance.

– Regenerative braking.

– “Start on demand” arrangements to avoid idleengines.

– Improved, more efficient power steering and other

subsystems.

– Active suspensions.

– Electrical valves and engine elements --

ultimately the self-starting engine.

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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 morethan about 2000 W, and are not efficient.

– A higher voltage system supports lower

current and loss.

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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 safetyissues.

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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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Safety Issues

• Industry premise: stay with an open electricalsystem for the foreseeable future.

• This philosophy supports the option for

evolutionary change of automotive electric

power.

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Safety Issues

• There are also “fully regulated” and “batteryregulated” 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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Safety Issues

• 12 V battery systems require undamagedoperation 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 arecharged at 42 V) without excessive possibility

of damage and spikes much beyond 60 V.

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Safety Issues

• In a fully regulated system, there is somebuffering between the battery and the rest of

the system.

• With full regulation, the wide swings of a

battery system are not necessarilyencountered 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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Safety Issues

• The term “42 V” refers to a range of choiceswith nominal battery levels in the range of

36 V to 48 V.

• While there is incomplete consensus, the

evolutionary approach would favor 36 Vbatteries (charging at 42 V).

• For comparison, we should take 42 V to

mean a tripling of present voltage, to give atleast triple the power.

• With better generation, power up to 5x is

available.

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Safety Issues

• We can also consider a “closed system,” inwhich 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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Power Levels

• At 42 V, a car’s electrical system rivals that ofa house.

• But, 10 kW is not enough for traction power.

Voltage Typicalpower level

Maximumpower level

12 V 1200 W 2000 W

42 V 5000 W 10 kW

300 V 30 kW 100 kW

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Architectures

• Each automotive voltage level hasadvantages 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 morerugged and more reliable at low voltages (but

they are disappearing).

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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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ENGINE42V

ALTERNATOR

42V

BATTERY

42V

LOADS

12V LOADS

DC – DC

Architectures

• Single battery at 42 V:

• Problem: jump starts?

• Problem: charge balance.

www.hoppecke.com

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ENGINE42V

ALTERNATOR

BIDIRECTIONAL

DC – DC

42V

BATTERY

42V

LOADS

12V LOADS

12V

BATTERY

Architectures

• Dual battery:

• The dc-dc converter mustbe bidirectional to support

starting and reliability.

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Grainger Center for Electric Machines and Electromechanics University of Illinois at Urbana-Champaign20

ENGINE

42V

STARTER/

ALTERNATOR

REGULATOR

42V

LOADS

12V LOADS

12V

BATTERY

BIDIRECTIONAL

DC – DC

Architectures

• 12 V battery

• Here a starter-alternatoris shown as well.

Source: Mechanical

Engineering Magazine

online, April 2002.

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ENGINE

42V

STARTER/

ALTERNATOR

42V

LOADS

LOADS

LOCAL

DC/DC

42V

BATTERY

Architectures

• Distributed converters with 42 V battery.

• Here there are many dc-dc

converters at the various

loads.

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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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Architectures

• Costs would seem to dictate a single-batteryarrangement.

• 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 (powerand 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 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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Connectors

• 150 A connector for 42 V (AMP, Inc.prototype).

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Points About Research Needs

• Many of the new challenges of 42 V havebeen addressed in other contexts:

– 48 V systems throughout the telephone network

(with battery regulation)

– Higher dc voltages in several aerospaceapplications (with bigger arcing problems in low-

pressure ambients)

• Methods need to be adapted to the low-cost

high-vibration automotive case.

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• 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)?

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• 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 sloweddown the development of 42 V systems.

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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 canbe controlled independent

of the engine.Source: Delphi Corp., Saginaw Steering Systems Div.

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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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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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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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Major Applications

• Electromechanical engine controls.• Valves.

• Fuel.Source: FEV Engine Technology, Inc.

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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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Major Applications

• Catalyst management systems and exhausttreatment.

• 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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Additional Applications

http://auto.mit.edu/consortia_dis.nsf/DocId/DA54330A7588430F852569CF00763577/$file/autot1.gif

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Mild Hybrids

• The key limitation of 42 V is that it really doesnot 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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Mild Hybrids

• A “light” hybrid or “mild” hybrid uses a smallmotor to manage

performance.

• The engine can be

shut down at stops.

• Braking energy

can be recovered.

• The car does not operate in an“all-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 socan 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 anISA and a mild hybrid.

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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

• All key

accessories areelectric.

• The Toyota hybridsystem operates at

288 V, and reaches

30 kW.

Source: www.familycar.com

http://www.familycar.com/RoadTests/ToyotaPrius/Images/HybridSystem.jpg

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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 andcontrols.

• Protection and semiconductor “fusing.”

• System-level analysis.

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Conclusion

• The continuing increase in electric powerlevels in automobiles will require highervoltages.

• 42 V systems (batteries at 36 V or 48 V) are

the highest possible in an “open” electricalsystem.

• There are fuel economy improvements just atthis 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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Why Not Just Big Batteries?

• Lead-acid battery energy density is onlyabout 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-based

hybrid 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-gen

diesel hybrid.

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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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• Toyota architecture

• Honda architecture:

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