The Nature and Promise of 42 V Automotive Power: An Update P. T. Krein Grainger Center for Electric Machinery and Electromechanics Department of Electrical

The Nature and Promise of 42 V The Nature and Promise of 42 V Automotive Power: An UpdateAutomotive Power: An Update

P. T. KreinP. T. Krein

Grainger Center for Electric Machinery and ElectromechanicsGrainger Center for Electric Machinery and Electromechanics

Department of Electrical and Computer EngineeringDepartment of Electrical and Computer Engineering

University of Illinois at Urbana-ChampaignUniversity of Illinois at Urbana-Champaign

Power Area and CEME Seminar, December 2002Power Area and CEME Seminar, December 2002

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

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OutlineOutline

• Why 42 V? Safety and other reasons.Why 42 V? Safety and other reasons.• Target power levels.Target power levels.• Architectures.Architectures.• Points about engineering research needs.Points about engineering research needs.• Major applications: power steering, Major applications: power steering,

starter-alternators, etc.starter-alternators, etc.• ““Mild hybrid” designs based on 42 V.Mild hybrid” designs based on 42 V.• Research opportunities.Research opportunities.• Conclusion.Conclusion.


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Why 42 V?Why 42 V?

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

• Electrical applications are beneficial for the Electrical applications are beneficial for the same reasons as for systems in aircraft:same reasons as for systems in aircraft:– Better efficiencyBetter efficiency– More flexible controlMore flexible control– Ease of energy conversionEase of energy conversion

• Low-cost control and conversion of energy is Low-cost control and conversion of energy is a key point.a key point.

• Electric power is rising because of electric Electric power is rising because of electric auxiliaries as well as more features.auxiliaries as well as more features.


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Why 42 V?Why 42 V?

• When electricity is used to power various When electricity is used to power various components (steering, brakes, suspension, components (steering, brakes, suspension, air conditioning), the results are better air conditioning), the results are better efficiency and more flexible performance.efficiency and more flexible performance.

• Performance is decoupled from the engine.Performance is decoupled from the engine.• Many estimates have been made, such as Many estimates have been made, such as

10% fuel economy improvements by simple 10% fuel economy improvements by simple electrification of existing functions.electrification of existing functions.


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Why 42 V?Why 42 V?

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

enhance performance.enhance performance.– Regenerative braking.Regenerative braking.– ““Start on demand” arrangements to avoid idle Start on demand” arrangements to avoid idle

engines.engines.– Improved, more efficient power steering and other Improved, more efficient power steering and other

subsystems.subsystems.– Active suspensions.Active suspensions.– Electrical valves and engine elements -- ultimately Electrical valves and engine elements -- ultimately

the self-starting engine.the self-starting engine.


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Why 42 V?Why 42 V?

• The conventional car is rapidly becoming more The conventional car is rapidly becoming more electric.electric.– The total electric load is about 1500 W today, The total electric load is about 1500 W today,

and is increasing toward 5000 W.and is increasing toward 5000 W.– Conventional alternators cannot deliver more Conventional alternators cannot deliver more

than about 2000 W, and are not efficient.than about 2000 W, and are not efficient.– A higher voltage system supports lower A higher voltage system supports lower

current and loss.current and loss.


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Why 42 V?Why 42 V?

• Three alternatives:Three alternatives:– Stick with 12 V. This limits effective power levels.Stick with 12 V. This limits effective power levels.– Get the voltage as high as possible (>100 V). This Get the voltage as high as possible (>100 V). This

requires a major overhaul of safety systems and requires a major overhaul of safety systems and basic designs.basic designs.

– Push the voltage as high as possible before Push the voltage as high as possible before significant safety issues come into play.significant safety issues come into play.

• 42 V tries to do the last: get the voltage as 42 V tries to do the last: get the voltage as high as possible while avoiding severe safety high as possible while avoiding severe safety issues.issues.


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Safety IssuesSafety Issues

• A car’s electrical system is typically “open.”A car’s electrical system is typically “open.”• Complicated wiring harnesses with close Complicated wiring harnesses with close

contact and hundreds of connections.contact and hundreds of connections.• Regulatory agencies have set a level of about Regulatory agencies have set a level of about

60 V dc as the maximum reasonable level in 60 V dc as the maximum reasonable level in an “open” system.an “open” system.

• Headroom is required to stay below this level Headroom is required to stay below this level under all allowed conditions.under all allowed conditions.


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

• This philosophy supports the option for This philosophy supports the option for evolutionary change of automotive electric evolutionary change of automotive electric power.power.


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• There are also “fully regulated” and “battery There are also “fully regulated” and “battery regulated” systems.regulated” systems.

• Battery-regulated system ultimately defer to Battery-regulated system ultimately defer to the battery to set the voltage level.the battery to set the voltage level.

• A battery-regulated system must allow forA battery-regulated system must allow for– Polarity reversalPolarity reversal– Disconnection: momentary or continuousDisconnection: momentary or continuous– Wide voltage swingsWide voltage swings

• Inductive spikes from corrosion or deliberate Inductive spikes from corrosion or deliberate disconnect are significant.disconnect are significant.


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• 12 V battery systems require undamaged 12 V battery systems require undamaged operation at –12 V or from short-term spikes operation at –12 V or from short-term spikes up to 75 V.up to 75 V.

• At higher battery voltages, surge suppressors At higher battery voltages, surge suppressors and other add-ons will be needed to limit and other add-ons will be needed to limit these extremes to present levels.these extremes to present levels.

• In a battery regulated system, 36 V is about In a battery regulated system, 36 V is about the highest possible level (but these are the highest possible level (but these are charged at 42 V) without excessive possibility charged at 42 V) without excessive possibility of damage and spikes much beyond 60 V.of damage and spikes much beyond 60 V.


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• In a fully regulated system, there is some In a fully regulated system, there is some buffering between the battery and the rest of buffering between the battery and the rest of the system.the system.

• With full regulation, the wide swings of a With full regulation, the wide swings of a battery system are not necessarily battery system are not necessarily encountered by the user.encountered by the user.

• 48 V batteries are possible within the 60 V 48 V batteries are possible within the 60 V limit, with such regulation.limit, with such regulation.

• The higher voltages also support extra The higher voltages also support extra efforts, such as anti-reversing diodes.efforts, such as anti-reversing diodes.


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• The term “42 V” refers to a range of choices The term “42 V” refers to a range of choices with nominal battery levels in the range ofwith nominal battery levels in the range of36 V to 48 V.36 V to 48 V.

• While there is incomplete consensus, the While there is incomplete consensus, the evolutionary approach would favor 36 V evolutionary approach would favor 36 V batteries (charging at 42 V).batteries (charging at 42 V).

• For comparison, we should take 42 V to For comparison, we should take 42 V to mean a tripling of present voltage, to give at mean a tripling of present voltage, to give at least triple the power.least triple the power.

• With better generation, power up to 5x is With better generation, power up to 5x is available.available.


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• We can also consider a “closed system,” in We can also consider a “closed system,” in which electrical contact is more protected.which electrical contact is more protected.

• Closed systems are used in today’s hybrid Closed systems are used in today’s hybrid and electric cars.and electric cars.

• The voltage levels there can exceed 300 V The voltage levels there can exceed 300 V dc.dc.


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Power LevelsPower Levels

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

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

VoltageVoltage Typical Typical power levelpower level

Maximum Maximum power levelpower level

12 V12 V 1200 W1200 W 2000 W2000 W

42 V42 V 5000 W5000 W 10 kW10 kW

300 V300 V 30 kW30 kW 100 kW100 kW


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ArchitecturesArchitectures

• Each automotive voltage level has Each automotive voltage level has advantages for some loads.advantages for some loads.

• 12 V or less for lamps, sensors,12 V or less for lamps, sensors,electronics, controls.electronics, controls.

• 42 V for motors, pumps, and fans.42 V for motors, pumps, and fans.• High voltage for electric tractionHigh voltage for electric traction

power.power.• Incandescent lamps, for example, are more Incandescent lamps, for example, are more

rugged and more reliable at low voltages (but rugged and more reliable at low voltages (but they are disappearing).they are disappearing).


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• Many possible architectures are possible.Many possible architectures are possible.• Most retain some 12 V capacity.Most retain some 12 V capacity.• They are typically divided into single-battery They are typically divided into single-battery

and dual-battery systems.and dual-battery systems.• There is no consensus on which to select, There is no consensus on which to select,

and we are likely to see several.and we are likely to see several.


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ENGINE42V

ALTERNATOR

42VBATTERY

42VLOADS

12V LOADS

DC–DC


• Single battery at 42 V:Single battery at 42 V:

• Problem: jump starts?Problem: jump starts?• Problem: charge balance.Problem: charge balance.

www.hoppecke.com


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ENGINE42V

ALTERNATOR

BIDIRECTIONALDC–DC

42VBATTERY

42VLOADS

12V LOADS

12VBATTERY


• Dual battery:Dual battery:

• The dc-dc converter mustThe dc-dc converter mustbe bidirectional to supportbe bidirectional to supportstarting and reliability.starting and reliability.


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ENGINE42V

STARTER/ALTERNATOR

REGULATOR

42VLOADS

12V LOADS

12VBATTERY

BIDIRECTIONALDC–DC


• 12 V battery12 V battery

• Here a starter-alternatorHere a starter-alternatoris shown as well.is shown as well.

Source: Mechanical Engineering Magazineonline, April 2002.


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ENGINE42V

STARTER/ALTERNATOR

42VLOADS

LOADS

LOCALDC/DC

42VBATTERY


• Distributed converters with 42 V battery.Distributed converters with 42 V battery.

• Here there are many dc-dcHere there are many dc-dcconverters at the variousconverters at the variousloads.loads.


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• The ultimate is a true multiplexed system:The ultimate is a true multiplexed system:– Deliver a single 42 V power bus throughout the Deliver a single 42 V power bus throughout the

vehicle, with a network protocol overlaid on it.vehicle, with a network protocol overlaid on it.– Local dc-dc converters provide complete local Local dc-dc converters provide complete local

operation and protection.operation and protection.– A ring bus or redundant bus structure could be A ring bus or redundant bus structure could be

used to enhance reliability.used to enhance reliability.– What about fuses? No central point is available.What about fuses? No central point is available.


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• Costs would seem to dictate a single-battery Costs would seem to dictate a single-battery arrangement.arrangement.

• However, this involves either a high-power However, this involves either a high-power 42V to 12V converter (bidirectional) or a 42V to 12V converter (bidirectional) or a troublesome 42 V battery.troublesome 42 V battery.

• Some researchers talk about a small dc-dc Some researchers talk about a small dc-dc converter just for jump starts.converter just for jump starts.

• Most systems are partially multiplexed (power Most systems are partially multiplexed (power and network distribution rather than individual and network distribution rather than individual loads).loads).


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IssuesIssues

• ““Key off” loads: sensors, alarms, clocks, Key off” loads: sensors, alarms, clocks, remote systems. All draw down power.remote systems. All draw down power.

• ““Flat” loads draw roughly fixed power, Flat” loads draw roughly fixed power, although the alternator output can vary.although the alternator output can vary.

• Connectors.Connectors.• Fusing.Fusing.• Arcs: much above 12 V, it becomes possible Arcs: much above 12 V, it becomes possible

to sustain an arc in close quarters.to sustain an arc in close quarters.


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ConnectorsConnectors

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


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Points About Research NeedsPoints About Research Needs

• Many of the new challenges of 42 V have Many of the new challenges of 42 V have been addressed in other contexts:been addressed in other contexts:– 48 V systems throughout the telephone network 48 V systems throughout the telephone network

(with battery regulation)(with battery regulation)– Higher dc voltages in several aerospace Higher dc voltages in several aerospace

applications (with bigger arcing problems in low-applications (with bigger arcing problems in low-pressure ambients)pressure ambients)

• Methods need to be adapted to the low-cost Methods need to be adapted to the low-cost high-vibration automotive case.high-vibration automotive case.


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• Motors are of keen interest.Motors are of keen interest.– Dc motors are cheap to build because of the Dc motors are cheap to build because of the

convenient wound-rotor structure.convenient wound-rotor structure.– The small machine design methods for cars do not The small machine design methods for cars do not

translate well to 42 V.translate well to 42 V.

• At 42 V, ac motors make sense.At 42 V, ac motors make sense.• But – small ac motors have been expensive But – small ac motors have been expensive

in most contexts.in most contexts.• How to build cheap, small ac motors (with How to build cheap, small ac motors (with

electronic controls)?electronic controls)?


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• Fusing is critical.Fusing is critical.• Power semiconductor circuits capable of Power semiconductor circuits capable of

acting as “self fuses” – active devices used acting as “self fuses” – active devices used as circuit breakers based on local sensing.as circuit breakers based on local sensing.

• Actual fuses and circuit breakers with cost-Actual fuses and circuit breakers with cost-effective arc management suitable for effective arc management suitable for automotive environments.automotive environments.

• Fusing issues (among others) have slowed Fusing issues (among others) have slowed down the development of 42 V systems.down the development of 42 V systems.


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Major ApplicationsMajor Applications

• Electric power steering.Electric power steering.• Two forms: assist pump and direct electric.Two forms: assist pump and direct electric.• The assist pump uses an electric motor to The assist pump uses an electric motor to

drive a conventional hydraulic unit.drive a conventional hydraulic unit.• The direct systemThe direct system

uses electric motors withuses electric motors withthe steering rack.the steering rack.

• In both cases, action canIn both cases, action canbe controlled independentbe controlled independentof the engine.of the engine.

Source: Delphi Corp., Saginaw Steering Systems Div.


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• Electric air conditioning.Electric air conditioning.• Remove the air conditioningRemove the air conditioning

system from engine belt drive.system from engine belt drive.• Provides much better controlProvides much better control

and flexibility.and flexibility.• Easier cycling,possibleEasier cycling,possible

heat pump application.heat pump application.


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• Integrated starter-alternator (ISA).Integrated starter-alternator (ISA).• Build an electric machine intoBuild an electric machine into

or around the flywheel.or around the flywheel.• Both permanent magnet andBoth permanent magnet and

induction types are beinginduction types are beingstudied.studied.

Source: Mechanical EngineeringMagazine online, April 2002.


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• Provides on-demand starts.Provides on-demand starts.• Supports regenerative braking.Supports regenerative braking.• The very fast dynamics of an ac machine The very fast dynamics of an ac machine

allows even active torque ripple cancellation.allows even active torque ripple cancellation.• If ripple can be cancelled, there is promise for If ripple can be cancelled, there is promise for

much quieter engines and much lower much quieter engines and much lower vibration levels.vibration levels.


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• Electromechanical engine controls.Electromechanical engine controls.• Valves.Valves.• Fuel.Fuel.

Source: FEV Engine Technology, Inc.


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• Active suspensions.Active suspensions.• Use electromechanical actuators in Use electromechanical actuators in

conjunction with mechanical suspension conjunction with mechanical suspension members.members.

• With enough actuator power, road bumps With enough actuator power, road bumps (large and small) can be cancelled with an (large and small) can be cancelled with an active suspension.active suspension.


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• Catalyst management systems and exhaust Catalyst management systems and exhaust treatment.treatment.

• Today, most automotive emissions occur in Today, most automotive emissions occur in the first few minutes of operation, when the the first few minutes of operation, when the catalyst is too cold to be effective.catalyst is too cold to be effective.

• Catalyst heaters or short-term exhaust Catalyst heaters or short-term exhaust management systems can drastically reduce management systems can drastically reduce tailpipe emissions in modern cars and trucks.tailpipe emissions in modern cars and trucks.

• Electrostatic precipitator methods can be of Electrostatic precipitator methods can be of value with diesel particulate exhaust.value with diesel particulate exhaust.


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Additional ApplicationsAdditional Applications

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


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Mild HybridsMild Hybrids

• The key limitation of 42 V is that it really does The key limitation of 42 V is that it really does not support electric traction power levels.not support electric traction power levels.

• As the promise of electric and hybrid vehicles As the promise of electric and hybrid vehicles becomes clearer, engineers push for higher becomes clearer, engineers push for higher power levels – beyond the reach of 42 V.power levels – beyond the reach of 42 V.

• A compromise is possible: the “mild hybrid” A compromise is possible: the “mild hybrid” vehicle.vehicle.


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• A “light” hybrid or “mild” hybrid uses a small A “light” hybrid or “mild” hybrid uses a small motor to managemotor to manageperformance.performance.

• The engine can beThe engine can beshut down at stops.shut down at stops.

• Braking energyBraking energycan be recovered.can be recovered.

• The car does not operate in anThe car does not operate in an“all-electric” regime.“all-electric” regime.

• The Honda Insight is a good example.The Honda Insight is a good example.

Source: www.familycar.com


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• For a mild hybrid approach, about 5 kW or so For a mild hybrid approach, about 5 kW or so can provide a useful level of “traction” power.can provide a useful level of “traction” power.

• The technique is accessible in a 42 V system, The technique is accessible in a 42 V system, although higher voltage (144 V in the Insight) although higher voltage (144 V in the Insight) is beneficial.is beneficial.

• A 42 V ISA has substantial promise for fuel A 42 V ISA has substantial promise for fuel economy improvements, and straddles the economy improvements, and straddles the boundary between a conventional car with an boundary between a conventional car with an ISA and a mild hybrid.ISA and a mild hybrid.


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Other HybridsOther Hybrids

• Higher-power hybrids require high voltage Higher-power hybrids require high voltage (240 V and up) for traction power.(240 V and up) for traction power.

• Electrical accessories are essential.Electrical accessories are essential.• Such cars can benefit from 42 V systems.Such cars can benefit from 42 V systems.


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Other HybridsOther Hybrids

• All key All key accessories are accessories are electric.electric.

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

Source: www.familycar.com

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


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Research OpportunitiesResearch Opportunities

• Low-cost small ac motor systems:Low-cost small ac motor systems:– 42 V dc bus42 V dc bus– Cheap invertersCheap inverters– Small ac motors that can be manufactured easilySmall ac motors that can be manufactured easily

• Engine electromechanical devices and Engine electromechanical devices and controls.controls.

• Protection and semiconductor “fusing.”Protection and semiconductor “fusing.”• System-level analysis.System-level analysis.


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ConclusionConclusion

• The continuing increase in electric power The continuing increase in electric power levels in automobiles will require higher levels in automobiles will require higher voltages.voltages.

• 42 V systems (batteries at 36 V or 48 V) are 42 V systems (batteries at 36 V or 48 V) are the highest possible in an “open” electrical the highest possible in an “open” electrical system.system.

• There are fuel economy improvements just at There are fuel economy improvements just at this level, but the extension to “mild hybrids” this level, but the extension to “mild hybrids” offers much more.offers much more.

• While the industry is now is a “go slow” mode While the industry is now is a “go slow” mode for 42 V, no one doubts its eventual use.for 42 V, no one doubts its eventual use.


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The End!The End!


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Why Not Just Big Batteries?Why Not Just Big Batteries?

• Lead-acid battery energy density is only Lead-acid battery energy density is only about 1% of that in gasoline.about 1% of that in gasoline.

• Our test car: 600 lb battery pack Our test car: 600 lb battery pack equivalent to one gallon of gas!equivalent to one gallon of gas!


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Electric and Hybrid GalleryElectric and Hybrid Gallery

• General Motors EV1.General Motors EV1.• 1300 lb battery pack at 1300 lb battery pack at

312 V, 102 kW motor.312 V, 102 kW motor.• 0-60 mph in less than 9 s.0-60 mph in less than 9 s.

• Volvo turbine-basedVolvo turbine-basedhybrid prototype.hybrid prototype.


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Electric and Hybrid Car GalleryElectric and Hybrid Car Gallery

• This Ford Escort was the first “true practical” This Ford Escort was the first “true practical” prototype hybrid – a complete station wagon.prototype hybrid – a complete station wagon.

• Second-genSecond-gendiesel hybrid.diesel hybrid.


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Toyota Hybrid SpecsToyota Hybrid Specs

• Small NiMH battery set, 288 V.Small NiMH battery set, 288 V.• 40 HP motor, ac permanent magnet type.40 HP motor, ac permanent magnet type.• Continuously-variable transmission with sun-Continuously-variable transmission with sun-

planet gear set for energy control.planet gear set for energy control.• 0-60 mph in about 17 s.0-60 mph in about 17 s.• 1500 cc engine can hold 75 mph indefinitely.1500 cc engine can hold 75 mph indefinitely.• Atkinson cycle engine (“5-stroke”) gets better Atkinson cycle engine (“5-stroke”) gets better

thermal efficiency but lower output torque.thermal efficiency but lower output torque.• Rated 54 mpg city, 48 highway.Rated 54 mpg city, 48 highway.


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• Toyota architecture Toyota architecture

• Honda architecture:Honda architecture:

Documents

The Nature and Promise of 42 V Automotive Power: An Update P. T. Krein Grainger Center for Electric Machinery and Electromechanics Department of Electrical