Power Electronics and 42 V Automotive Power US-Jordan Workshop, 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 • The growth of automotive power electronics. • Why 42 V? Power levels, accessories, safety, and other reasons. • Single and two-battery architectures. • Multiplexed power. • Major applications: power steering, starter-alternators, etc. • “Mild hybrid” designs based on 42 V. • Conclusion.
The Growth of Auto Power Electronics • Power electronics for transportation is a major growth area. • Management of 12 V power • Audio systems • Motor controls • The move to higher voltages extends the reach in many ways. • The ultimate application is electric traction (but it is not really the most important!).
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. • Many estimates have been made, such as 10% fuel economy improvements just be using a higher voltage.
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.
Why 42 V? • The conventional car is rapidly becoming more electric. • A new car can contain up to 100 motors. • The total electric load is about 1000 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? Car motor usage is growing fast. It will soon rise to 200 electric motors per car. Source: Johnson Electric, 1999.
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 • When there is no special electrical regulation, 36 V batteries are the maximum. • In a fully regulated system, 48 V batteries are possible within the 60 V limit. • The term “42 V” refers to a range of choices with nominal battery levels in the range of36 V to 48 V. • For comparison, we should take 42 V to mean a tripling of voltage, to give about triple the power.
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 • A car’s electrical system rivals that of a house.
Architectures • Each automotive voltage level has advantages for some loads. • 12 V 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.
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. • Fuse coordination is important. • 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 alternatoroutput can vary. • Connectors, 150 A • Fusing. • Arcs: much above 12 V,it becomes possible tosustain an arc. Source: Amp, Inc.
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 conditioningor heat pumps. • 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. • Provides on-demand starts. • Supports regenerative braking. • One prototype was even usedto cancel engine torquepulsations with active motorcontrol. Source: Mechanical EngineeringMagazine online, April 2002.
Major Applications • Electromechanical engine controls. • Valves. • Fuel. Source: FEV Engine Technology, Inc.
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 is the minimum “traction” power. • The technique is accessible in a 42 V system, although higher voltage (144 V in the Insight) is beneficial. • One hesitation for 42 V is the marginal ability to support traction power and hybrid designs. • A 42 V ISA has substantial promise for fuel economy improvements.
Key Power Electronics Needs • Low-cost dc-dc converters. • High-power bidirectional dc-dc converters. • Low-cost 42 V inverters for small ac drives. • Small ac motor designs, 100 W and below. • “Semiconductor fuse” automatic protection circuits. • Improved battery and system management. • High momentary power drivers for engine electromechanics.
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.