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 • 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? • 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 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 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 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 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 • 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 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 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 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 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 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 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 • At 42 V, a car’s electrical system rivals that of a house. • But, 10 kW is not enough for traction power.
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).
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.
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
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.
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.
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.
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.
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 • “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 • 150 A connector for 42 V (AMP, Inc. prototype).
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 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 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 • 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 Applications • Electric air conditioning. • Remove the air conditioningsystem from engine belt drive. • Provides much better controland flexibility. • Easier cycling,possibleheat pump application.
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 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 Applications • Electromechanical engine controls. • Valves. • Fuel. Source: FEV Engine Technology, Inc.
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 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 • 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 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 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 • 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.
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 • 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 • 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? • 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!
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 • This Ford Escort was the first “true practical” prototype hybrid – a complete station wagon. • Second-gendiesel hybrid.
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 Gallery • Toyota architecture • Honda architecture: