Power Electronics and 42 V Automotive Power P. T. Krein Grainger Center for Electric Machinery and Electromechanics Department of Electrical and Computer

Power Electronics and 42 V Power Electronics and 42 V Automotive PowerAutomotive Power

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

US-Jordan Workshop, December 2002US-Jordan Workshop, 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

• The growth of automotive power The growth of automotive power electronics.electronics.

• Why 42 V? Power levels, accessories, Why 42 V? Power levels, accessories, safety, and other reasons.safety, and other reasons.

• Single and two-battery architectures.Single and two-battery architectures.• Multiplexed power.Multiplexed power.• 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.• Conclusion.Conclusion.


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The Growth of Auto Power ElectronicsThe Growth of Auto Power Electronics

• Power electronics for transportation is a Power electronics for transportation is a major growth area.major growth area.– Management of 12 V powerManagement of 12 V power– Audio systemsAudio systems– Motor controlsMotor controls

• The move to higher voltages extends the The move to higher voltages extends the reach in many ways.reach in many ways.

• The ultimate application is electric traction The ultimate application is electric traction (but it is not really the most important!).(but it is not really the most important!).


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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.

• Many estimates have been made, such as Many estimates have been made, such as 10% fuel economy improvements just be 10% fuel economy improvements just be using a higher voltage.using a higher voltage.


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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.Electrical valves and engine elements.


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Why 42 V?Why 42 V?

• The conventional car is rapidly becoming The conventional car is rapidly becoming more electric.more electric.– A new car can contain up to 100 motors.A new car can contain up to 100 motors.– The total electric load is about 1000 W today, and The total electric load is about 1000 W today, and

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

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

and loss.and loss.


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Why 42 V?Why 42 V?

Car motor usage is growing fast.Car motor usage is growing fast.It will soon rise to 200 electric motors per car.It will soon rise to 200 electric motors per car.Source: Johnson Electric, 1999.Source: Johnson Electric, 1999.


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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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• When there is no special electrical regulation, When there is no special electrical regulation, 36 V batteries are the maximum.36 V batteries are the maximum.

• In a fully regulated system, 48 V batteries are In a fully regulated system, 48 V batteries are possible within the 60 V limit.possible within the 60 V limit.

• 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.

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


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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

• A car’s electrical system rivals that of a A car’s electrical system rivals that of a house.house.

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 for lamps, sensors, electronics,12 V for lamps, sensors, electronics,controls.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.rugged and more reliable at low voltages.


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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.– Fuse coordination is important.Fuse coordination is important.

• 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 alternatoralthough the alternatoroutput can vary.output can vary.

• Connectors, 150 A Connectors, 150 A • Fusing.Fusing.• Arcs: much above 12 V,Arcs: much above 12 V,

it becomes possible toit becomes possible tosustain an arc.sustain an arc.

Source: Amp, Inc.


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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 conditioningElectric air conditioningor heat pumps.or heat pumps.

• Remove the air conditioningRemove the air conditioningsystem from engine belt drive.system from engine belt drive.

• Provides much better controlProvides much better controland flexibility.and flexibility.

• Easier cycling,possibleEasier cycling,possibleheat 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.• Provides on-demand starts.Provides on-demand starts.• Supports regenerative braking.Supports regenerative braking.• One prototype was even usedOne prototype was even used

to cancel engine torqueto cancel engine torquepulsations with active motorpulsations with active motorcontrol.control. Source: Mechanical Engineering

Magazine online, April 2002.


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

Source: FEV Engine Technology, Inc.


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Mild HybridsMild Hybrids

• 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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Mild HybridsMild Hybrids

• For a mild hybrid approach, about 5 kW or so For a mild hybrid approach, about 5 kW or so is the minimum “traction” power.is the minimum “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.

• One hesitation for 42 V is the marginal ability One hesitation for 42 V is the marginal ability to support traction power and hybrid designs.to support traction power and hybrid designs.

• A 42 V ISA has substantial promise for fuel A 42 V ISA has substantial promise for fuel economy improvements.economy improvements.


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Key Power Electronics NeedsKey Power Electronics Needs

• Low-cost dc-dc converters.Low-cost dc-dc converters.• High-power bidirectional dc-dc converters.High-power bidirectional dc-dc converters.• Low-cost 42 V inverters for small ac drives.Low-cost 42 V inverters for small ac drives.• Small ac motor designs, 100 W and below.Small ac motor designs, 100 W and below.• ““Semiconductor fuse” automatic protection Semiconductor fuse” automatic protection

circuits.circuits.• Improved battery and system management.Improved battery and system management.• High momentary power drivers for engine High momentary power drivers for engine

electromechanics.electromechanics.


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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.

Documents

Power Electronics and 42 V Automotive Power P. T. Krein Grainger Center for Electric Machinery and Electromechanics Department of Electrical and Computer