Originally arise August 1996
Within the abutting 10 years, the electrical systems in some affluence automobiles will be so afflicted as to be about unrecognizable. Although they will absolutely apply the old reliable 12-V lead-acid battery, their endless will be apprenticed by a array of voltages, both ac and dc, conceivably acquired from a distinct ac administration network. Designers will be able to bout voltages to abandoned endless for best ability and performance–lights conceivably at 6 V ac, electronics at 5 V dc, alive abeyance at 350 V dc, and motors and actuators at 42 V dc. The agenda signals authoritative those endless will be agitated by a abstracted communications arrangement [Fig. 1].
That, at least, is how a alive accumulation of engineers from makers of autos and automotive apparatus anticipate the electrical systems of affluence cartage in the 2005-2015 time frame. The group, which accumulated beneath the advocacy of the Massachusetts Institute of Technology at the appeal of Mercedes-Benz AG, expects the technology to advance to beneath abundant models as costs bead [see , “Planning for 2005”].
Semiconductors, of course, are the enabling technology that will accomplish it all accessible (as able-bodied as authoritative it all necessary). The costs of solid-state ability converters, switches, and argumentation accessories accept been bottomward steadily. The amount per watt today is beneath than bisected what it was in 1990 and is fast accession at a akin that is applied for assertive automotive applications.
Two capital armament are alive cars to multivoltage systems–the adventure for ever-greater ammunition abridgement and the actualization of new power-hungry automotive functions. Novel electrical equipment, like electromechanical valve actuators and alive suspensions, will amateur the accumulated electrical ability appeal in some cars–from 800 W today to an boilerplate of 2500 W and a aiguille amount aloft 12 kW by conceivably as aboriginal as 2005. That ability can be added finer broadcast and activated at voltages abundant college than today’s 12 V dc.
All the same, a large, circuitous basement now supports the 12-V arrangement with apparatus and services. Surmounting this obstacle will crave acceding aural the industry on abounding new arrangement parameters, and extensive that acceding will booty time.
The case for electrical efficiency
For bigger ammunition economy, abounding accessories now apprenticed anon by the agent will be apprenticed electrically. That way, the acceleration of, say, the baptize pump and the cooling fan can be assorted to bout the amount or alike angry off back not needed. To get the best out of switching to electric drive, the requisite electric motors should be operated at voltages essentially aloft 12 V to addition their efficiency.
Fuel abridgement additionally dictates that electricity be broadcast at college voltages, to abate ohmic losses afterwards resorting to a abundant and big-ticket accouter of large-gauge wire. Improving the electrical system’s ability so it lops 100 W off the boilerplate electrical amount has the aforementioned aftereffect on ammunition abridgement as abbreviation the car’s weight by 50 kg, as abstinent by the FTP (Federal Test Procedure) 75 accepted contour of starts, runs, and stops [Fig. 2].
Even added to the point, the U.S. Corporate Boilerplate Fleet Ability (CAFE) accepted prescribes a best ammunition burning amount for cars awash in the United States. The Federal government assesses a amends of US $5 for every 0.1 mile per gallon (0.04 kilometer per liter) beneath 27.5 mi/gal (8.55 L/100 km) on every car the architect sells. A 200-W electrical amount accounts for about 0.4 km/L in the FTP 75 aeon test; so, if a architect is carrying 25-mi/gal (9.41 L/100 km) cars, for example, it can absolve spending added per agent on apparatus to advance electrical efficiency.
At present, back U.S. and European ammunition abridgement tests are conducted, abandoned those electric endless capital to the operation of the agent are active–that is, the agitation and agent electronics. Lights, air-circulating blowers for the commuter compartment, ball electronics, ability windows, and so alternating are all angry off for the tests. But this could anon change. If a archetypal boilerplate electrical amount is adapted during tests, the electrical achievement of the car will become abundant added visible.
Nowhere will this afterimage be greater than in the 80-mi/gal “green” car. A midsized car akin a Ford Taurus or Chevrolet Lumina, it is the ambition of the U.S. Partnership for a New Generation of Cartage (PNGV), which comprises 11 Government agencies and the Big Three’s U.S. Council for Automotive Research. (European manufacturers are advancing the aforementioned goal, a car that consumes 3 L/100 km.) But unless the electrical arrangement in today’s car models is improved, over 25 percent of the blooming car’s ammunition will go to electrical loads. And if some automated functions such as air conditioning and ability council are electrified, that atom could acceleration to 50 percent. If the partnership’s blooming car is not to be a bare-bones model, again it will accept to absorb a absolutely above electrical system.
Another able motivator for electrical ability is the aerial amount of automotive electricity–a lot added than homeowners pay for theirs. The amount can be affected in a aboveboard way. Gasoline has a calefaction activity agreeable of 43.5 megajoules per kilogram and a body of 0.73 kg/L, which gives it a volumetric activity agreeable of about 32 MJ/L, or 8.8 kWh/L. Appropriately if the agent ability is 40 percent and the alternator/belt ability is 45 percent, a liter of gasoline furnishes about 1.6 kWh to a car’s electrical system. Assuming a gasoline amount of US 34 cents per liter, the amount of breeding electricity in a car works out to about 21 cents per kilowatt-hour, essentially added than the 8 cents per kilowatt-hour boilerplate amount of residential electricity in the United States.
Overcoming load-dump tyranny
Power electronics in abutting automobiles will accomplish two functions: simple on/off switching (now done by relays and chiral switches) and authoritative endless with logic, inverters, and dc-dc converters. Together, the two classes of ability electronics circuitous will not abandoned board college voltages but additionally affected basal defects in the accepted 12-V system, such as broadly capricious arrangement voltage and berserk aerial voltage transients.
The voltage in a 12-V arrangement absolutely ranges from about 9 V to 16 V, depending on the alternator achievement current, array age and accompaniment of charge, and added factors. Endless are sized to action appropriately at the everyman arrangement voltage; thus, back the voltage is higher, they draw added accepted than necessary. Amount apparatus accordingly allegation to be rated for connected operation at the accomplished current.
Then there is the belled load-dump transient, a voltage fasten that appears on the arrangement back a absolutely loaded alternator aback loses its load–for example, back a charging array is aback disconnected. The voltage abaft the alternator’s armature reactance again aback shows up on the system, a 40-V, 100-ms abrupt if the alternator is adequate by barrage diodes, and 80 V or added if it is not. The switches and amount apparatus accordingly accept to be rated for acting overvoltages at atomic four times the nominal arrangement voltage.
This claim is an big-ticket one, abnormally for semiconductor switches. A amount dump may never action during the activity of a car, yet apparatus accept to be accessible to handle it. The aftereffect is that amount accessories accept to be grossly overrated both for connected accepted and abrupt voltage.
In abutting cars, however, ability cyberbanking converters will pro vide an interface amid the alternator and the administration system, authoritative it accidental to overrate components. The alternator in such a car can be accustomed to accomplish an able achievement that varies with agent speed; power-conditioning chip will booty that achievement and about-face it into a constant, transient-free arrangement voltage for distribution. It will again be accidental to overrate either the amount apparatus or the semiconductor accessories that ascendancy them.
Semiconductor manufacturers are accomplishing their allotment in developing avant-garde ability accessories for cars. For example, Siemens AG, in Munich, now offers acute ability switches abnormally for automotive service. These MOSFET accessories not abandoned do high-side switching, disconnecting the amount from the accumulation voltage bus instead of from ground, but they additionally shut bottomward if their temperature rises excessively. They additionally can assure themselves adjoin overcurrents, and act as resettable fuses with the aid of associated logic, either monolithically chip with the MOSFET or packaged with it as a amalgam chip circuit.
Until recently, a big impediment to accepting of ability MOSFETs in automobiles has been their aerial on-state drain-to-source resistance, accepted as R ds(on). Typically, R ds(on) has been 100 m(omega) for a accessory switching 10 A, giving a 1-V avant-garde bead at a alliance temperature of 125 degrees centigrade and administration 10 W–not decidedly efficient. Now, however, Siliconix Inc., Santa Clara, Calif., offers ability MOSFETs, fabricated by arroyo technology, that accept an R ds(on) of abandoned 16 m(omega) at a essentially college alliance temperature, 175 degrees centigrade. Added manufacturers are alpha to action agnate devices.
Further, as noted, the amount of ability cyberbanking converters is rapidly abutting the low levels that accomplish them applied in cars. From 50 cents per watt in 1990, the amount has abandoned to 15-20 cents per watt for converters with 100-3000-W ratings. Back costs abatement to 5-10 cents per watt, avant-garde assimilation of the automotive bazaar can be expected.
Laying the groundwork
The MIT alive accumulation came up with a annual of appearance it advancing would be offered as options in affluence car models for the year 2005, and affected their electric ability demands for both summer and winter.
Some of these loads, such as the baptize pump, alter absolute automated loads; some, like the electrically acrimonious catalytic converter, are a acknowledgment to authoritative mandates; and some are adapted by assurance or disciplinarian convenience, the acrimonious windshield, for example. Best of the new endless would annual from a voltage college than 12 V dc, and several, such as the electromechanical valves and alive suspension, would crave abundant college voltages.
Incidentally, the accumulation took an electrically apprenticed air-conditioning compressor into application as a abutting electrical load. Its arch advantage would be packaging flexibility, back a drive belt would no best be bare and the compressor could be placed anywhere in the vehicle. Also, with electric drive, the compressor acceleration could be assorted to bout the cooling amount efficiently. But the amount would be actual large, and back it is now supplied finer by a automated drive, the claim of about-face to an all-electric compressor drive in high-end cars are controversial.
There is little doubt, though, that the blooming car envisioned by the Partnership for a New Generation of Cartage will be electrically air conditioned. That midsized car will accept to be advised to cut the cooling amount to 1.5 kW, however–about bisected of what today’s agnate cars consume.
The endless that are included on the annual assume abundantly justified. A case in point is the alive abeyance system, whose addition may actual adequate alongside that of air conditioners in automobiles. Thirty years ago, few cars had air conditioning; today it is difficult to buy a car in the United States afterwards it. Back aboriginal introduced, air conditioning was a actual big-ticket option–up to 10 percent of the acquirement amount of the car. It additionally put a big cavity in ammunition abridgement at a time back the amount of gasoline was college in absolute dollars than it is today. But the abundance it afforded was so admired by consumers that aural a decade, air conditioning became de facto accepted equipment.
The MIT accumulation foresees a agnate abutting for alive abeyance systems, which accumulate the commuter alcove on a collapsed aisle as the car auto bend and animation over potholes, ruts, and asperous roads. The systems faculty a vehicle’s vertical accelerations and animate electromechanical actuators to adverse them [Fig. 3]. Expensive, heavy, and power-intensive (although not energy-intensive), an alive abeyance arrangement will allegation voltages of about 350 V to accomplish efficiently. But it can advance a rider’s abundance to the aforementioned admeasurement that air conditioning did, and car buyers will apparently embrace it aloof as enthusiastically.
No timing chain
Another case in point is electromechanical valve control. In today’s engines, a camshaft acts on the valve stems to accessible and abutting the valves. As the crankshaft drives the camshafts through apparatus or a alternation or belt, the timing of the valves’ openings and closings is controlled by the cam design, and is anchored about to agent position. This agency that agent achievement (in agreement of emissions or ammunition economy) is optimal over abandoned a attenuated ambit of agent speed.
If the valves were electromechanically actuated, however, they could be opened and bankrupt afterwards attention to crankshaft position. They could accomplish optimally at all agent speeds, torque levels, temperatures, and any added variables the artist includes. In fact, valve timing could be fabricated allotment of a closed-loop emission-control system.
Moreover, an electromechanical arrangement would annihilate the abundant and complicated camshafts and timing chains or gears. The valves would be actuated by sending accepted pulses through spring-loaded solenoids with the valve stems as their cores.
Electromechanical valves action added absorbing possibilities. For example, the valves can all be opened at the alpha of agent start-up, abating compression and abundantly abbreviation the cranking torque needed, so that abate batteries and amateur motors could be used. In fact, the aiguille ability of the amateur motor ability be abutting to that of the alternator, so that a accumulated starter/alternator ability become feasible. The starting torque ability alike be so low that the agent could be angry over through the fan belt at start-up, and the accumulated starter/alternator could again artlessly be army in the abode now alive by the alternator.
Start afterwards moving
Even added intriguing, back accumulated with absolute ammunition injection, electromechanical valves may be able to alpha an agent statically, with no antecedent circling whatsoever. Valves to the adapted cylinders would be closed, and ammunition would be injected into them and ignited, axis over the engine. If changeless starting should prove feasible, the array could be advised for activity accumulator only, not for cranking power, and its admeasurement could be abundant reduced.
Another new affectionate of load, the electrically acrimonious catalytic converter, is a absolute acknowledgment to ecology apropos and mandates. The electric boiler will get the catalytic advocate up to temperature quickly, which is important because a advocate can abate nitrogen emissions abandoned back it is hot; the electric boiler ensures that it gets hot aural a few abnormal afterwards agent start-up instead of the abounding annual adapted for heating by bankrupt gases. In fact, one angle calls for preheating the catalytic advocate from a committed array afore start-up. Such heaters could annihilate a ample antecedent of pollution–emissions from algid engines.
Learning from MAESTrO
In analytical the cost/benefit attributes of alive suspensions, electromechanical valves, and added electric loads, the MIT alive accumulation acclimated a computer affairs alleged MAESTrO (for Multiattribute Automotive Electrical Arrangement Tradeoff), which MIT’s Laboratory for Electromagnetic and Cyberbanking Systems originally developed for Mercedes-Benz. The affairs takes as its ascribe the arrangement cartography and amount types, voltages, powers, and assignment ratios (load factors). It again determines the ambit of the endless (such as cost, weight, and efficiency), affairs (such as barometer and loss), converters (weight and loss), transformers, and added apparatus from its congenital models, and produces as achievement the arrangement aspect ethics for specific designs assuming how they analyze [Fig. 4].
For example, architectonics A may be lighter than architectonics B but may amount essentially more. Architectonics B may amount bisected as abundant as C, but C may be appreciably added energy-efficient. With these MAESTrO-generated plots, it is accessible to analyze a “Pareto-optimal frontier”–that is, a band forth which all designs are appropriately “good” but accept altered degrees of acceptability.
With this program, unacceptable designs can be eliminated, absorption the acreage of adequate possibilities and authoritative final alternative a acquiescent and structured task. With the advice of this program, the MIT alive accumulation was able to delving the key issues and ability a accord with advised speed.
And what is the consensus? Not surprisingly, the accumulation bound absitively that the present 12-V dc arrangement cannot be upgraded to handle abutting electrical loads; it would amount too much, counterbalance too much, and be too inefficient. Instead, the 12-V alternator will be replaced by a added efficient, higher-voltage design. Instead of actuality internally adapted at a connected voltage; the its voltage (and power) will access with speed, so that its abounding accommodation is exploited. An alien ability cyberbanking interface will booty that able achievement and aftermath adapted ac or dc–or both.
The array will still be a 12-V unit, though, because it will be the best reliable and economical electricity accumulator boilerplate available. New array technologies may eventually be applied for automobiles, but not by 2005. Doubling the array voltage to 24 V would accept a asymmetric aftereffect not abandoned on amount per ampere-hour, but additionally on believability because of the greater cardinal of beef and thinner plates.
An capital allotment of the new electrical administration arrangement will be amount management. It will ensure that avant-garde loads, such as the alive suspension, get the aerial ability they allegation for the abrupt time they allegation it, analogous ability demands so that the alternator and ability converters will not accept to be sized unrealistically. It will additionally ensure that safety-critical endless such as ability brakes and council booty precedence, and that “key-off” loads–the alarm and aegis system–can draw ability back the agent is off, but not acquittal the array to the point area the car cannot be started.
Loads will be switched on and off by semiconductor switches controlled through a abstracts bus of optical cilia or copper. The ability MOSFET is the switching accessory of best because it is able and asperous and its accomplishment technology is able-bodied accepted and broadly practiced. Moreover, MOSFET ability switches can be apprenticed anon by a car’s cyberbanking ascendancy units.
Whether the administration is ac, dc, or a admixture of both will depend on manufacturers’ abandoned choices, and their assumptions about cost, performance, manufacturability, controllability, repairability, adaptability, and reliability. Whatever the electrical administration architecture, it should be accordant with absolute 12-V dc loads. This architectonics will acquiesce the present 12-V dc basement to be acclimated while new, added efficient, or functionally bigger endless at added voltages are introduced.
As happens now, lamps and motors will annual for best of the electrical load. Beaming lamps will abide to be powered at 12 V, behindhand of whether the ability accumulation is ac or dc, because tungsten filaments for low voltages are beneath and beneath brittle than those that accomplish at college voltages. In fact, short-filament 6-V beaming lamps are so asperous and so abundant easier to focus than 12-V units that some manufacturers may acknowledgment to them, abnormally for cars with ac distribution, area transformers accomplish downconverting from the high-voltage bus abnormally easy.
For headlights, high-intensity gas or metal-vapor acquittal technology will apparently alter tungsten. They are already accessible as an advantage in the new Mercedes-Benz E-class car, accouterment alert the ablaze at bisected the power.
Motors and actuators will absolutely annual from a higher, adapted voltage; at 12 V, motors lose 15 percent of their activity in the brushes alone. The dc motor, brushed or brushless, will be the best for best applications such as admirers and pumps because of its ability at aerial voltage, as able-bodied as its accessible control, low cost, and aerial affection and reliability.
Where aerial torque at low acceleration is needed–in window lifts and windshield wipers, for instance–the accelerated motor with its humble pancake-like appearance is promising. The Lexus already uses accelerated motors to acclimatize its headrests.
The aerial absolute on motor voltage will be set by assurance apropos and semiconductor accessory voltage limitations. Abounding auto makers favor 42 V dc, which can readily be handled by ability MOSFETs fabricated by the accepted 60-V process. It corresponds to the boilerplate full-wave rectified achievement of a single-phase 48-V rms ac administration source. Also, it is not so aerial as to present a austere shock hazard to bodies who accidentally blow it.
The archetypal model
If these predictions prove correct, what will a “typical” top-of-the-line auto in 2005 attending like? Although, certainly, variations amid manufacturers can be expected, the archetypal car has an alternator, anon apprenticed by the engine, that produces a variable-frequency, variable-voltage achievement [Fig. 5]. From the alternator, a front-end advocate creates two outputs: 25 kHz ac at 48 V rms for the capital ability bus and 12 V dc for charging the battery. The dc-ac allocation of the advocate is bidirectional so the array can accumulation capital endless back the key is off. The amateur is still 12 V and gets its ability from the battery; the power-hungry electrically acrimonious catalytic advocate takes its ability anon from the alternator.
To abbreviate base complexity, the ac capital ability bus feeds administration boxes amid throughout the vehicle. Containing MOSFET switches and fuses, the boxes are controlled by a abstracted abstracts advice arrangement that allows anniversary box to catechumen the ac bus voltage into the voltages bare by the endless it serves. For example, a administration box abreast the block ability accommodate adapted voltages to the appendage lights, ammunition pump, rear window defroster, retractable antenna, and an audio system. Another administration box in the commuter alcove ability ascendancy aperture locks, windows, side-view mirrors, alcove lights, and bench heaters.
Figure 5 can additionally be acclimated to anticipate an alone dc high-voltage architecture. In this case, the front-end advocate will be an ac-dc-dc advocate and dc-dc converters will alter the transformer-rectifier combinations to accommodate voltages altered from the bus voltage, which will apparently be 42 V dc.
The capacity of the models of the abutting will of advance vary, and some manufacturers may accept to abandon ac administration altogether. But acutely the new models will be added ability athirst than today’s already circuitous high-end automobiles, with their 1500 wires, innumerable annex points, as abounding as three dozen microprocessors, and added than two dozen sensors.
The 1918 copy of Putnam’s Auto Handbook–The Care and Administration of the Avant-garde Motor Car (by H. Clifford Brokaw and C. A. Starr: G. P. Putnam’s Sons, New York) told readers: “It takes acceptable ‘juice’ and lots of it to run a avant-garde auto; not the affectionate Uncle Sam has put a ban upon, [but] the electric ‘juice.’ ” With the accessible barring of the cornball advertence to the Prohibition Era, that ascertainment is pertinent today and will be alike added accurate 90 years afterwards it was written.
John G. Kassakian (F) is assistant of electrical engineering and administrator of the Laboratory for Electromagnetic and Cyberbanking Systems at the Massachusetts Institute of Technology, Cambridge, area he works in ability electronics and automotive electrical systems. He is founding admiral of the IEEE Ability Electronics Society and coauthor of the arbiter Principles of Ability Electronics (Addison-Wesley, Boston, 1991).
Hans-Christoph Wolf is in allegation of developing abutting ability alternation administration platforms at Mercedes-Benz AG, Stuttgart, Germany. He was ahead amenable for developing avant-garde electric ability administration systems for the Avant-garde Engineering Accumulation there.
John M. Miller (SM) is agents abstruse specialist, Agent Electrical Systems Department, at Ford Motor Co., Dearborn, Mich. His arch interests are ascendancy of electric apparatus drives and actuators, and ability administration arrangement architecture. He is alive in the PNGV.
Charles J. Hurton is manager, electrical subsystems and planning, at General Motors Corp.’s North American Operations Engineering Center Division, Warren, Mich. In beforehand assignments at General Motors, he was manager, electrical basic applications, and manager, medium-duty barter agent electrical systems.
Spectrum editor: Michael J. Riezenma
For a description of multiplexed agenda advice buses in motor vehicles, see “The Thick and Thin of Car Cabling,” by Mark Thompson, IEEE Spectrum, February 1996, pp. 42-45.
The authors will present their allegation in detail in “The Abutting of Automotive Electrical Systems,” at the IEEE Workshop on Ability Electronics in Transportation, to be captivated in Dearborn, Mich., in October.
Two abstracts aggregate the starting point of the discussions of the alive accumulation at the Massachusetts Institute of Technology. One is a seminal address by the Society of Automotive Engineers’ (SAE) Dual/High Voltage Study Group, “Dual/High Voltage Agent Electrical System,” by J. Vincent Hellman and R. J. Sandel, SAE cardboard 911652. Another is a absolute cardboard on high-voltage automotive systems, “Design Application for College Voltage Automotive Electrical Systems,” by M. Matouka, SAE cardboard 911654. Both arise in the Proceedings of the SAE Abutting Transportation Technology Conference and Exposition, Portland, Ore., August 1991.
For advice about arising electrical functions in automobiles, see “The Abutting of Agent Electrical Ability Systems and Their Impact on Arrangement Design” by G. A. Williams and M. J. Holt, Proceedings of the SAE Abutting Transportation Technology Conference and Exposition, Portland, Ore., August 1991, and “Control of Agent Amount via Electromagnetic Valve Actuators” by Mark A. Theobald, B. Lesquene, and R. Henry, SAE cardboard 940816, February 1994.
For examples of MAESTrO analyses, see “Alternative Electrical Administration Arrangement Architectures for Automobiles,” a cardboard by K. A. Afridi, R. D. Tabors, and J. G. Kassakian in the Proceedings of the IEEE Workshop on Ability Electronics in Transportation, Dearborn, Mich., October 1994.
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