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Currently, the situation in the automotive in-dusty is such that the demands for higher fuel economy and more electric power are driving advanced vehicular power system volt-ages to higher levels. For example, the projected increase in total power demand is estimated to be about three to four times that of the current value. This means that the total future power De-and of a typical advanced vehicle could roughly reach a value as high as 10 k. In order to satisfy this huge vehicular load, the AP-approach is to integrate power electronics intensive solutions within advanced vehicular power systems.
In view of this fact, this paper aims at reviewing the present situation as well as projected future research and development work Of advanced vehicular electrical power systems including those of electric, hybrid electric, and fuel cell vehicles (Eves, Have, and OFFS). The paper Will first introduce the proposed power system architectures for Have and Offs and Will then go on to exhaustively discuss the specific applications Of dc}dc and dc/AC power electronic converters in advanced automat-dive power systems.
Index Terms-??Electric propulsion, electric vehicles (Eves), fuel cell vehicles (Offs), hybrid electric vehicles (Have), internal combustion engines, motor drives, power converters, semiconductor devices. L. INTRODUCTION BY THE time the centralization of the next-generation car comes around, advanced power electronics and motor drives will have already established themselves as prime comps-nets of advanced vehicular drive trains. Advanced power ILEC-tropic converters and traction motor drives will be responsible for a major part of the vehicle’s energy usage.
As of now, the automotive market is making rapid developments in case of the hybrid electric vehicles (HAVE)_ Commercially available Have include the Toyota Pries, Toyota Highlander Hybrid, Toyota Campy Hybrid, Lexus REXES h, Honda Insight, Honda Civic Hybrid, Honda Accord Hybrid, and Ford Escape Hybrid. In the case of future Have, power electronic converters and associated motor drives, Which control the flow Of electrical energy within the HAVE power system, promise to be the keys to making Have more fuel efficient and emit lower harmful pollutants.
Manuscript received March 15, 2005; revised October 26, 2005. Recon. Mended by Associate Editor J. Sheen. The authors are with Electric Power and Power Electronics Center, Illinois Institute of Technology, Chicago, IL 60616993 USA (e-mail: emadi@iit. Due). Digital Object Identifier 10. 1 109/DEPLETED. 872378 As is well known, in the first half of the past century, the 6-V electrical system in automobiles served the purpose of ignition, cranking, and a satisfying few lighting loads Since then, there has been a constant rise in vehicular power requirement. Reference loads, such as electric steering, that were tradition-ally driven by mechanical, pneumatic, and hydraulic systems, are now increasingly being replaced by the electrically driven systems, in order to increase the performance and efficiency of operation. Furthermore, luxury loads have also increased over time, imposing a higher demand Of electrical popover 13]. It must be pointed out here that the rate of increase of automotive loads is assumed to be about per year.
Thus, such load demands have resulted in the need to scale up the onboard vehicular power level. Considering these aspects, several decades ago, the voltage was raised from its earlier 6-V level to the present day 12. V level and, now with an ever-in-creasing demand forecasted into the future, there is a need to switch over to much higher voltage levels of 42 V, 300 V, or higher, as the ease may he Due to the high voltage levels being produced in Have, it becomes essential to have dc/dc converters to supply all the auxiliary loads on board the vehicle.
Although the dc/dc converter technology is well develop-opted for low-power applications at lower cost, much work needs to be done for high- power applications, It is an immense chalk-Lange to meet all the vehicle standards tort electromagnetic in-deterrence (MME) and electromagnetic compatibility (EMCEE) as well as specifications of reliability and packaging [41, In ad-edition, power electronic converters also dictate how and when fuel/electricity is used in Have. A suitable dc/AC inverter draws dc power from the batteries to drive the electric traction motor, which in turn provides power to the wheels.
The dc/AC inverter also performs the function of recharging the batteries during re-generative braking in Have. Based on this fundamental background, proving the criticality of power electronics for HAVE applications, this paper will review the role of power electronics and compare the associated advanced power system architectures for HAVE as well as electric vehicle (EVE) and fuel cell vehicle (FCC) applications. The vary-souse design issues for power electronics intensive HAVE and C.V. power yester and the current and future trends will be high-lighted.
In addition, the proposed 42-V Powered is also focused upon, emphasizing on the description of its key capabilities and requirements. Furthermore. The paper will also discuss the mild hybrid vehicle, wherein the major opportunities for automotive power electronics are outlined. Finally, few system-level issues 0885-8993620. 00 C 2006 IEEE 568 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOLVO. 21, NO. 3, MAY 2006 Fig. 1. Conventional 14-V dc power system architecture, that drive the relative power electronics size and cost functions will also be addressed.
II. CONVENTIONAL AUTOMOTIVE POWER SYSTEMS AND I Fig. 2. Typical representation of the more electric hybrid vehicle power system I CONCEPT OF MORE ELECTRIC VEHICLES (MEW architecture During the mid sass, the automotive industry decided to I opt for 12-V electrical power Systems for vehicles, since the I then popular 6-V system was rapidly becoming plagued by the and rear-wheel steering, which will be driven electrically in the I I increasing vehicular load demands.
The battery became a six- I future. I cell module instead of three cells, at approximately the same As is well documented in related literature, most Of the if-I energy rating. The electrical system demand had risen from the true advanced electric loads require power electronic controls. Sociopath early costs typically about 1 k by the sass, In advanced future vehicles, power electronics is forecasted tool I as more and more electrically powered devices were installed I perform three major tasks.
First task is simple on,’off switching | | of loads, which is performed by mechanical switches and relays I The conventional electrical system in an automobile can I in conventional cars The second task is to act as a suitable essentially be divided into he architectural elements of energy controller electric traction motors, I storage, generation, starting, and distribution.
The Finally, power electronics I distribution I intensive power systems will not only be used for the obvious I system of a conventional 14-V power system satisfies vehicular I task of changing system voltage levels, but also for converting I I loads such as, interior/exterior lighting, electric motor driven electrical power from one form to another, using dc/dc, dc}AC, I fans/pumps/compressors, and instrumentation subsystems 16]. And AC/dc converters. I A simple rendition f the conventional 14-V electric power I As mentioned earlier, due to the ever- increasing electrical system architecture is shown in Pig.
I. Loads, the automotive industry is opting for more electric powers I As is clear from Fig. 1, the conventional power system AR- systems. Due to this, Moves will need highly reliable and fault- arrangement has a single 14-V dc voltage level, with the vehicle- tolerant electrical power systems to deliver high quality power alular loads being controlled by manual switches and relays. As I from the source to the electrical loads. It is extremely important mentioned earlier, the resent average power demand in an AU- I that the voltage level/form in which power is distributed be taken I automobile is approximately 1 k.
The voltage in a 14-V system care of. A higher voltage will reduce the weight and volume I actually varies between 9 and 16 V at the battery terminals, De- I of the wiring harness, among several other advantages 171, | pending on the alternator output current, battery age, state of Fig. 2 shows the concept of a future hybrid MOVE, making use charge, and various other minor factors [7]. This results in thigh voltage (300 V) automotive power system architecture. I I overrating the loads at nominal system voltage.
In addition to Currently, the proposed Moves are at a transitional stage, in- I these disadvantages, the present 14-1/ system cannot handle if- I valuing different systems voltage levels It is expected that I true electrical loads to be introduced in the more electric nevi- the future MOVE power systems will most likely be comprised of I I ornament of the future cars, as it would be expensive and infix- I a single main voltage bus (high voltage) with a provision for why-l cent to do so.
I brie (dc and AC), multivariate level distribution and intelligent I In more electric vehicles (MOVE), there is a trend toward energy and load management. I I expanding electrical loads and replacement of mechanical I I and hydraulic systems With more electrical systems. These Ill. ADVANCED DRIVE ARRANGEMENTS FOR ELECTRIC, I I loads include lights, pumps, fans, and electric motors for vary- I HYBRID ELECTRIC, AND FUEL CELL VEHICLES souse functions.
In addition, they also include some advanced, electrically assisted vehicular loads, such as power steering, This section introduces the various drive train arrangements air conditioner/ compressor, electromechanical valve control, of pure battery electric vehicles EVE), series/parallel/series-par- active suspension,’vehicle dynamics, and catalytic converter allele/complex HAVE drive trains, and pure FCC/hybrid FCC | [6].
Furthermore, additional advanced vehicular loads include, drive trains. Based on the review done in this section, the anti-lock braking, throttle actuation, ride-height adjustment, ensuing sections will focus on the power electronics intensive MAID POWER ELECTRONICS INTENSIVE SOLUTIONS | 569 Pig. 3. Topological arrangement for an electric vehicle (EVE) drive train. Power system architectures for these advanced drive train arrangements, A.
Battery Electric Vehicle (EVE) Drive Train Topology A purely electric drive system principally replaces the internal combustion engine (ICE) and the various transmit-soon systems with an all-electric system. As is well known, rechargeable chemical batteries are the traditional option as en-erg; sources for Eves. But they tend to be heavy and expensive to replace over their limited lifetimes. In addition to traditional batteries like lead-acid, nickel metal- hydride (In-MM). ND nickel-cadmium (In-Cd), there are advanced technologies like lithium-polymer (Lie. Polymer) and lithium-ion (Lie-ion) bat. Rise. Despite the popularity that these advanced batteries have gained for portable electronic applications, they haven’t quite maintained the same reputation for use in Eves. Most practical Eves still use lead-acid batteries, with the more sophisticated ones using In-MM batteries [8], A basic overview of a battery electric vehicle (BEE) is as shown in Fig. 3.
More recently, the automotive industry is cutting back on EVE production, and has declared Have and Offs to be the future of advanced vehicle technologies. This is because Bees cost sis-munificently more than gasoline vehicles, due to the fact hat EVE battery modules are currently being produced in very small volt-mums [l I], Higher vehicle prices are partially offset by the fact that fuel costs for battery electrics are about one-third those of a gasoline-powered vehicle. In addition, Bees have fewer moving parts than gasoline cars, and hence, require less maintain- nuance.
The future of battery Eves is somewhat uncertain at this time, but their development has already made important contra-options to advancing electric drive train and storage technology-gees needed by both Have as well as Offs [10], [I I]. If further breakthroughs in battery technologies occur, Bees could yet prove o be the future of clean transportation. B. Series HAVE Drive Train Topology A series hybrid vehicle is basically an electric vehicle with an on-board battery charger.
An ICE is generally run at an optimal efficiency point to drive the generator and charge the propel-soon batteries on-hoard the vehicle, as shown in Fig. 4. When the state of charge (SOC) of the battery is tat predetermined minimum, the ICE is turned on to charge the battery The ICE turns off again when the battery has reached a desired-able maximum SOC. The engine/ generator set maintains the battery charge around It must he noted that, in a SE- Fig. 4. Typical layout off series HAVE drive train. Fig. 5. Schematic of a parallel HAVE drive train configuration. Sis HAVE, there is no mechanical connection between the ICE and the chassis. The advantage with the series HAVE configuration is that the ICE is running mostly at its optimal combination of speed and torque, thereby, having a low fuel consumption and high Effie-science. However, there are two energy conversion stages during the transformation of the energy between the ICE and the wheels (ICE/generator and generator/motor) [16], [17]. Some energy is lost because of the Vivo-stage power conversion process. A SE-rise hybrid vehicle is more applicable in city driving.
C. Parallel HAVE Drive Train Topology A hybrid vehicle with the parallel configuration has both the ICE and the traction motor mechanically connected to the trans-mission. A schematic figure of the parallel hybrid is shown in Fig. S. The vehicle can be driven with the ICE, or the electric motor, or both at the same time and, therefore, it is possible to choose the combination freely to feed the required amount of torque at any given time In parallel HAVE, there are many ways to configure the use of the ICE and the traction motor.
The most widely used strategy is to use the motor alone at low speeds, since it is more efficient than the ICE, and then let the ICE work alone at higher speeds. When only the ICE is in use, the traction motor can function as a generator and charge the battery. A parallel HAVE can also have a continuously variable transmission (C.V.) instead of a fixed step transmission [19], [20]. With this technique, it is POS-Siebel to choose the most efficient operating points for the 570 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOLVO. 21, NO. 3, MAY 2006 Fig. 6. Typical drive train configuration of a series-parallel combined HAVE.
Fig. 7. Schematic off complex HAVE drive train. At given torque demands freely and continuously. The result is lower fuel consumption due to the inherently more efficient fuel usage. Energy is also saved due to regenerative braking. The advantage with the parallel HAVE configuration is that there are fewer energy conversion stages compared to the series HAVE and, therefore, a lesser part of the energy is lost [19]. In fact, the parallel HAVE drive train depicts fairly lower losses compared to other HAVE topologies and, hence, has a compare-Tivoli higher overall drive train efficiency, D.
Series-parallel HAVE Drive Train Topology The series-parallel HAVE is a combination of the series and parallel hybrids. There is an additional mechanical link between the generator and the electric motor, compared to the series con-figuration, and an additional generator compared to the parallel hybrid, as shown in Pig. With this design, it is possible to com- bins the advantages of both the series and parallel HAVE confining-orations [201. It must be highlighted here that the series-parallel HAVE is also relatively more complicated and expensive.
There are many possible combinations of the ICE and traction motor. Two major classifications can be identified as electric-in-tensile and engine-intensive. The electric-intensive series-par-allele HAVE configuration indicates that the electric motor is more active than the ICE for propulsion, whereas, in the engine-intent. Sieve case, the ICE is more active [201, [211. A common opera-dive characteristic for both types of series-parallel HAVE systems is that the electric motor is used alone at start with ICE turned off, During normal driving, the ICE alone propels the vehicle in the engine-intensive case.
On the other hand, the ICE and electric tutor propel the vehicle in the electric-intensive case 120], When acceleration is needed, the electric traction motor is used in combination with the ICE to give extra power in both of the configurations. During braking or deceleration, the tract-Zion motor is used as a generator to charge the battery and, in stand still, the ICE can continue to run and drive the generator to charge the battery, if needed, Another form of series-hybrid configuration is shown in Fig, 7, which is a power split HAVE topology.
This topology includes a planetary gearbox, which connects the ICE, traction motor, and generator. Varying the speed from the two planetary gear pinions, connected to the electric motor and the generator, can control the ICE speed. When the ICE turns Off, the vehicle is propelled in the pure electric mode. However, at most Of the operating points, the energy flows in a similar fashion to either that of a parallel HAVE or to that Of a series HAVE- In parallel HAVE mode, energy flows from ICE via the gearbox to the wheels. Whereas, in the series HAVE mode of operation, the energy flows from generator and motor to the wheels [21].
The proportion between these two energy flows depends on the overall vehicle speed. Under most operating conditions, this configuration is a combination of series and parallel hybrid vehicle, It is also possible to operate this in parallel mode for some operating conditions. One of the motivating factors for use of the power split HAVE topology is to increase the vehicle power capability for a given transmission, This in turn enables the usage to continuously variable transmission concept for light duty HAVE propulsion AP-applications, such as pick up trucks and small buses, E.
FCC Drive Train Topology The potential for superior efficiency and zero (or near zero) emissions has long attracted interest to fuel cells as the potential automotive engine of the future. However, systematic efforts to realize the efficiency and emissions benefits of fuel cells in the transportation sector have materialized only in the last 10 years. The overall goal of ongoing fuel cell research and development programs is to develop a fuel cell engine that will give vehicles the range of conventional cars, while attaining environmental benefits comparable to those Of battery-powered electric viii-clues.
Although the technology is currently quite expensive, fuel cells Offer benefits including high overall efficiency and quiet operation due to few moving parts. A typical fuel cell based propulsion system is shown in Fig. 8. The hydrocarbon fuel such as gasoline, natural gas, methanol, or ethanol is first reformed to obtain the required hydrogen using a reformer (or fuel processor) [221. This hydrogen rich gas from the reformer is fed to the anode of the fuel cell. It is also possible to store the on-board the vehicle using a pressurized cylinder, instead of using the reformer for con-verging the fuel to -rich gas.
The oxygen (or air) is Ted in to the cathode fuel cell. Depending on the fuel cell stack counting- ration, and the flow of hydrogen and oxygen, the fuel cell stack produces the dc output voltage [22], [23]. The fuel cell stack MAID teal. : POWER ELECTRONICS INTENSIVE SOLUTIONS | 571 Fig. 8. Typical topological arrangement off hybrid fuel cell vehicle drive train. Output is fed to the power conditioner (power electronic con-vertex) to obtain the required output voltage and current. Did-ally, the popover conditioner must have minimal losses leading to a higher efficiency.
Power conditioning efficiencies can type-call/ be higher than [24]. Lb. POWER ELECTRONICS INTENSIVE POWER SYSTEM ARCHITECTURES FOR HAVE A. Advanced Electrical Features in Future HAVE Technologies As mentioned earlier, there is a trend in the automotive in-dusty to replace more engine driven mechanical and hydraulic loads with electrical loads, due to higher efficiency, safety re-acquirement, and drivers comfort. All of these new functions re-quire the application of power electronics. In most of the cases, the cost to the power electronics dominates the argument to in-traducing such functions.
Many of these functions will only AP-pear in concept vehicles in the projected future. Some of these include luxury loads, such as information and entertainment that have received lots of hype recently The other class of features is -by wire, where stands for an advanced function such as, “steer or “brake. ” Another class of advanced electrical features includes power steering pump, electric AC-dive suspension system, electromechanical valve control, ILEC-tribally heated catalytic converter, air-conditioning systems, and water/oil/fuel pumps [25].
There are also other loads such as throttle actuation, ride-height adjustment, rear-wheel steering, Which are proposed to be driven electrically in the future. F-gig_ g depicts a summary of some of the future electrical features emotive power systems. It is virtually mandatory that most Of the proposed future electric loads Will indeed require power ILEC-tropic controls of some sort. B. Advanced HAVE Topology Using SIS System In view of research and development work for Moves, it must be pointed out that one of the leading breakthroughs in the AU. Emotive industry is the introduction of the integrated starter-generator (SIS) system for mild Have [261. The SIS is primarily an electric machine with a rotor instead of a flywheel mounted on the rankest between the ICE and transmission, A schematic diagram of an SIS system used in conjunction with a high-voltage vehicular power system is shown in Fig. 10, The Fig. 9. Future electrical features in more electric vehicle power systems. Fig. 10. Integrated starter-alternator (SIS) based HAVE drive train.
SIS provides the functions of an electric starter and an alternator [26], [27]. By using suitable advanced power electronic con-vertex systems, it is possible for the SIS to compensate the drive train Oscillations to provide more comfort. The power electronic converter system controls the SIS operating state, depending n the load Status and the battery charge Status. Improved fuel economy and reduced emissions are NON prime advantages Of an SIS system. Using a start/stop cycle, the ICE is turned off during deceleration or after the vehicle comes to a complete stop.
The SIS can be used to propel the vehicle from a stop condition (and/or at a set speed), to restart the ICE. The SIS will also be able to route power produced by regenerative braking into the energy storage devices (batteries or ultra-caps-traitors) [26], [27]. It can also be used to provide power enhance-meet, when taking off from a stop, or in added acceleration for passing. C. 42-V/12-V Dual-Voltage Vehicular Electrical Systems The 42-V,’1 2-V dual-voltage architecture is being popularly touted as one of the solutions for the ever-increasing in-vehicle load demand.
The operating voltage criteria being considered for 42-V systems are shown in Fig, I I _ The maximum dynamic over voltage is limited to 58 V, including the transient voltages 572 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOLVO. 21, NO. 3, MAY 2006 Pig. I l. Typical operating voltage criteria for 42-V HAVE power systems, Pig. 13. Schematic of a dual voltage (14 V and 42 V) architecture using one battery. Fig. 12. Schematic of a dual voltage (14 V and 42 V) architecture using two batteries. [28]. In this case, the system charging voltage is set at 42 V.
The entire electrical system in the vehicle is run at a nominal value of 42 V, whenever the engine is running. Some of the advantages of such a system include, high efficiency and performance, less expensive operational procedures, reduced total installed power due to the integration of the mechanical and hydraulic power into the electrical power system, and reduction in the overall design complexity, The transition to an entirely 42-V dominated architecture cannot be done immediately. Therefore, it is assumed that a dual voltage automotive power system will exist at least for a while.
There are various ways to implement a power electronics intensive dual voltage power system. The schematic used in Fig. 12 illustrates a dual (42 V-??14 V) battery system. Fig. 13 shows a schematic using only one single 42-V battery, and Fig. 14 illustrates a structure in which the dual voltage is generated by a single alternator, which has two output voltages. In the dual battery system, the first (36-V) battery is optimized for high power delivery, while the second (12-V) battery is optimized for low powers to purport key-off loads plus hazard lamp operation [28], [29].