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Power Electronics Intensive Solutions Essay Abstract—There is a clear trend in the automotive industry to use more electrical systems in order to satisfy the ever-growing ve-hicular load demands. Thus, it is imperative that automotive elec-trical power systems will obviously undergo a drastic change in the next 10–20 years. Currently, the situation in the automotive in-dustry 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-mand of a typical advanced vehicle could roughly reach a value as high as 10 kW. In order to satisfy this huge vehicular load, the ap-proach 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 (EVs, HEVs, and FCVs). The paper will first introduce the proposed power system architectures for HEVs and FCVs and will then go on to exhaustively discuss the specific applications of dc/dc and dc/ac power electronic converters in advanced automo-tive power systems. Index Terms—Electric propulsion, electric vehicles (EVs), fuel cell vehicles (FCVs), hybrid electric vehicles (HEVs), internal com-bustion engines, motor drives, power converters, semiconductor devices. I. INTRODUCTION. BY THE time the commercialization of the next-generation car comes around, advanced power electronics and motor drives will have already established themselves as prime compo-nents of advanced vehicular drive trains. Advanced power elec-tronic 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 (HEVs). Commercially available HEVs include the Toyota Prius, Toyota Highlander Hybrid, Toyota Camry Hybrid, Lexus RX 400 h, Honda Insight, Honda Civic Hybrid, Honda Accord Hybrid, and Ford Escape Hybrid. In the case of future HEVs, power electronic converters and associated motor drives, which control the flow of electrical energy within the HEV power system, promise to be the keys to making HEVs more fuel efficient and emit lower harmful pollutants. Manuscript received March 15, 2005; revised October 26, 2005. Recom-mended by Associate Editor J. Shen. The authors are with Electric Power and Power Electronics Center, Illinois Institute of Technology, Chicago, IL 60616-3793 USA (e-mail: [emailprotected] edu). Digital Object Identifier 10. 1109/TPEL. 2006. 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 [1]–[5]. Since then, there has been a constant rise in vehicular power requirement. Performance 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 power [3]. It must be pointed out here that the rate of increase of automotive loads is assumed to be about 4% 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 case may be [3]–[5]. Due to the high voltage levels being produced in HEVs, 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 devel-oped for low-power applications at lower cost, much work needs to be done for high-power applications. It is an immense chal-lenge to meet all the vehicle standards for electromagnetic in-terference (EMI) and electromagnetic compatibility (EMC) as well as specifications of reliability and packaging [4], [5]. In ad-dition, power electronic converters also dictate how and when fuel/electricity is used in HEVs. 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 HEVs. Based on this fundamental background, proving the criticality of power electronics for HEV applications, this paper will re-view the role of power electronics and compare the associated advanced power system architectures for HEV as well as electric vehicle (EV) and fuel cell vehicle (FCV) applications. The var-ious design issues for power electronics intensive HEV and FCV power systems and the current and future trends will be high-lighted. In addition, the proposed 42-V PowerNet 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 0885-8993/$20. 00  © 2006 IEEE 568IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 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| Fig. 2. Typical representation of the more electric hybrid vehicle power system| | CONCEPT OF MORE ELECTRIC VEHICLES (MEV)| | || architecture. | | During the mid 1950s, the automotive industry decided to| | | opt for 12-V electrical power systems for vehicles, since the| | | then popular 6-V system was rapidly becoming plagued by the| and rear-wheel steering, which will be driven electrically in the| | increasing vehicular load demands. The battery became a six-| future. | | cell module instead of three cells, at approximately the same| As is well documented in related literature, most of the fu-| | energy rating. The electrical system demand had risen from the| ture advanced electric loads require power electronic controls. | | 100 W of the early 1900s to typically about 1 kW by the 1990s,| In advanced future vehicles, power electronics is forecasted to| | as more and more electrically powered devices were installed| perform three major tasks. First task is simple on/off switching| | [6]–[8]. | of loads, which is performed by mechanical switches and relays| | The conventional electrical system in an automobile can| in conventional cars [7]. The second task is to act as a suitable| | essentially be divided into the architectural elements of energy| controller for electric traction motors. Finally, power electronics| | storage, generation, starting, and distribution. The distribution| intensive power systems will not only be used for the obvious| | system of a conventional 14-V power system satisfies vehicular| task of changing system voltage levels, but also for converting| | loads such as, interior/exterior lighting, electric motor driven| electrical power from one form to another, using dc/dc, dc/ac,| | fans/pumps/compressors, and instrumentation subsystems [6]. | and ac/dc converters. | | A simple rendition of the conventional 14-V electric power| As mentioned earlier, due to the ever-increasing electrical| | system architecture is shown in Fig. 1. | loads, the automotive industry is opting for more electric power| | As is clear from Fig. 1, the conventional power system ar-| systems. Due to this, MEVs will need highly reliable and fault-| | rangement has a single 14-V dc voltage level, with the vehic-| tolerant electrical power systems to deliver high quality power| | ular loads being controlled by manual switches and relays. As| from the source to the electrical loads. It is extremely important| | mentioned earlier, the present average power demand in an au-| that the voltage level/form in which power is distributed be taken| | tomobile is approximately 1 kW. The voltage in a 14-V system| care of. A higher voltage will reduce the weight and volume| | actually varies between 9 and 16 V at the battery terminals, de-| of the wiring harness, among several other advantages [7], [8]. | | pending on the alternator output current, battery age, state of| Fig. 2 shows the concept of a future hybrid MEV, making use| | charge, and various other minor factors [6], [7]. This results in| of high voltage (300 V) automotive power system architecture. | | overrating the loads at nominal system voltage. In addition to| Currently, the proposed MEVs are at a transitional stage, in-| | these disadvantages, the present 14-V system cannot handle fu-| volving different systems voltage levels [8]. It is expected that| | ture electrical loads to be introduced in the more electric envi-| the future MEV power systems will most likely be comprised of| | ronment of the future cars, as it would be expensive and ineffi-| a single main voltage bus (high voltage) with a provision for hy-| | cient to do so.| brid (dc and ac), multivoltage level distribution and intelligent| | In more electric vehicles (MEVs), there is a trend toward| energy and load management. | | expanding electrical loads and replacement of mechanical| | | and hydraulic systems with more electrical systems. These| III. ADVANCED DRIVE TRAIN ARRANGEMENTS FOR ELECTRIC,| | loads include lights, pumps, fans, and electric motors for var-| | | | HYBRID ELECTRIC, AND FUEL CELL VEHICLES| | ious 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 (EV), series/parallel/series-par-| | active suspension/vehicle dynamics, and catalytic converter| allel/complex HEV drive trains, and pure FCV/hybrid FCV| | [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| |. EMADI et al. : POWER ELECTRONICS INTENSIVE SOLUTIONS| 569| Fig. 3. Topological arrangement for an electric vehicle (EV) drive train. power system architectures for these advanced drive train arrangements. A. Battery Electric Vehicle (EV) Drive Train Topology A purely electric drive system principally replaces the internal combustion engine (ICE) and the various transmis-sion systems with an all-electric system. As is well known, rechargeable chemical batteries are the traditional option as en-ergy sources for EVs. 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 (Ni–MH), and nickel–cadmium (Ni–Cd), there are advanced technologies like lithium–polymer (Li-polymer) and lithium–ion (Li–ion) bat-teries. Despite the popularity that these advanced batteries have gained for portable electronic applications, they haven’t quite maintained the same reputation for use in EVs. Most practical EVs still use lead-acid batteries, with the more sophisticated ones using Ni–MH batteries [8], [9]. A basic overview of a battery electric vehicle (BEV) is as shown in Fig. 3. More recently, the automotive industry is cutting back on EV production, and has declared HEVs and FCVs to be the future of advanced vehicle technologies. This is because BEVs cost sig-nificantly more than gasoline vehicles, due to the fact that EV battery modules are currently being produced in very small vol-umes [9]–[11]. 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, BEVs have fewer moving parts than gasoline cars, and hence, require less mainte-nance. The future of battery EVs is somewhat uncertain at this time, but their development has already made important contri-butions to advancing electric drive train and storage technolo-gies needed by both HEVs as well as FCVs [10], [11]. If further breakthroughs in battery technologies occur, BEVs could yet prove to be the future of clean transportation. B. Series HEV 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 propul-sion batteries on-board the vehicle, as shown in Fig. 4. When the state of charge (SOC) of the battery is at a predetermined minimum, the ICE is turned on to charge the battery [12]–[15]. The ICE turns off again when the battery has reached a desir-able maximum SOC. The engine/generator set maintains the battery charge around 65%–75%. It must be noted that, in a se- Fig. 4. Typical layout of a series HEV drive train. Fig. 5. Schematic of a parallel HEV drive train configuration. ries HEV, there is no mechanical connection between the ICE and the chassis. The advantage with the series HEV configuration is that the ICE is running mostly at its optimal combination of speed and torque, thereby, having a low fuel consumption and high effi-ciency. 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 two-stage power conversion process. A se-ries hybrid vehicle is more applicable in city driving. C. Parallel HEV 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. 5. 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 [18]–[20]. In parallel HEV, 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 HEV can also have a continuously variable transmission (CVT) instead of a fixed step transmission [19], [20]. With this technique, it is pos-sible to choose the most efficient operating points for the ICE 570IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 21, NO. 3, MAY 2006 Fig. 6. Typical drive train configuration of a series-parallel combined HEV. Fig. 7. Schematic of a complex HEV 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 HEV configuration is that there are fewer energy conversion stages compared to the se-ries HEV and, therefore, a lesser part of the energy is lost [19]. In fact, the parallel HEV drive train depicts fairly lower losses compared to other HEV topologies and, hence, has a compara-tively higher overall drive train efficiency. D. Series-Parallel HEV Drive Train Topology The series-parallel HEV 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 Fig. 6. With this design, it is possible to com-bine the advantages of both the series and parallel HEV config-urations [20]. It must be highlighted here that the series-parallel HEV 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-tensive and engine-intensive. The electric-intensive series-par-allel HEV configuration indicates that the electric motor is more active than the ICE for propulsion, whereas, in the engine-inten-sive case, the ICE is more active [20], [21]. A common opera-tive characteristic for both types of series-parallel HEV 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 motor propel the vehicle in the electric-intensive case [20]. 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 trac-tion 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 HEV 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 HEV or to that of a series HEV. In parallel HEV mode, energy flows from ICE via the gearbox to the wheels, whereas, in the series HEV 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 HEV topology is to increase the vehicle power capability for a given transmission. This in turn enables the usage of continuously variable transmission concept for light duty HEV propulsion ap-plications, such as pick up trucks and small buses. E. FCV 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 vehi-cles. 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) [22]. 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-verting the fuel to -rich gas. The oxygen (or air) is fed in to the cathode fuel cell. Depending on the fuel cell stack configu-ration, and the flow of hydrogen and oxygen, the fuel cell stack produces the dc output voltage [22], [23]. The fuel cell stack EMADI et al. : POWER ELECTRONICS INTENSIVE SOLUTIONS| 571| Fig. 8. Typical topological arrangement of a hybrid fuel cell vehicle drive train. output is fed to the power conditioner (power electronic con-verter) to obtain the required output voltage and current. Ide-ally, the power conditioner must have minimal losses leading to a higher efficiency. Power conditioning efficiencies can typ-ically be higher than 90% [24]. IV. POWER ELECTRONICS INTENSIVE POWER SYSTEM ARCHITECTURES FOR HEVS A. Advanced Electrical Features in Future HEV Technologies As mentioned earlier, there is a trend in the automotive in-dustry to replace more engine driven mechanical and hydraulic loads with electrical loads, due to higher efficiency, safety re-quirements, and driver’s comfort. All of these new functions re-quire the application of power electronics. In most of the cases, the cost of the power electronics dominates the argument of in-troducing 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 â€Å"† stands for an advanced function such as, â€Å"steer† or â€Å"brake. † Another class of advanced electrical features includes power steering pump, electric ac-tive suspension system, electromechanical valve control, elec-trically 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. Fig. 9 depicts a summary of some of the future electrical features auto-motive power systems. It is virtually mandatory that most of the proposed future electric loads will indeed require power elec-tronic controls of some sort. B. Advanced HEV Topology Using ISA System In view of research and development work for MEVs, it must be pointed out that one of the leading breakthroughs in the au-tomotive industry is the introduction of the integrated starter-generator (ISG) system for mild HEVs [26]. The ISG is pri-marily an electric machine with a rotor instead of a flywheel mounted on the crankshaft between the ICE and transmission. A schematic diagram of an ISG 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 (ISA) based HEV drive train. ISG provides the functions of an electric starter and an alternator [26], [27]. By using suitable advanced power electronic con-verter systems, it is possible for the ISG to compensate the drive train oscillations to provide more comfort. The power electronic converter system controls the ISG operating state, depending on the load status and the battery charge status. Improved fuel economy and reduced emissions are two prime advantages of an ISG system. Using a start/stop cycle, the ICE is turned off during deceleration or after the vehicle comes to a complete stop. The ISG can be used to propel the vehicle from a stop condition (and/or at a set speed), to restart the ICE. The ISG will also be able to route power produced by regenerative braking into the energy storage devices (batteries or ultra-capac-itors) [26], [27]. It can also be used to provide power enhance-ment, 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/12-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. 11. The maximum dynamic over voltage is limited to 58 V, including the transient voltages 572IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 21, NO. 3, MAY 2006 Fig. 11. Typical operating voltage criteria for 42-V HEV power systems. Fig. 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 support key-off loads plus hazard lamp operation [28], [29]. In other words, in this structure, the starting function will be isolated from the storage function required for â€Å"key-off† loads. This architecture provides oppor-tunities to improve existing high power loads by moving them to the 42-V side. It also minimizes changes to existing 14-V features, like lighting loads. However, this system has two batteries, which when com-pared with today’s one 14-V battery, implies more cost, weight, and packaging space. The other new component in this system is Fig. 14. Schematic of a dual stator dual voltage (14 V and 42 V) architecture using two batteries. the 42-V/14-V dc/dc converter. The overall cost of power elec-tronics is still considered too high for automotive applications. However, power electronic converters are capable of providing seamless energy transfer between two energy storage batteries and help improve reliability of some critical vehicular functions, which require a backup battery. In contrast, the single battery schematic of Fig. 13 is based on the desire to avoid cost, weight, and packaging problems cre-ated by the additional battery. The idea is that the power man-agement system should be smart enough to manage the key-off loads from depleting the high-voltage battery to the point that the vehicle cannot be started [29]. It is critical to point out here that this architecture also uses a bidirectional dc/dc converter be-tween the 42-V and 14-V buses. The schematic shown in Fig. 14 uses a more complicated alternator, with two sets of stator wind-ings, to provide power separately to the 42-V and 14-V buses. In this structure, again, high power loads are connected to the 42-V bus and the 14-V bus supplies low-power electrical mod-ules [29]. In addition to the above-described architectures, there exist many other strategies and variations of dual-voltage automo-tive power systems. The auto industry at this point is stagnant with regards to selecting appropriate dual-voltage MEV archi-tectures. One of the main focal points of research in selecting EMADI et al. : POWER ELECTRONICS INTENSIVE SOLUTIONS a suitable MEV system is to determine which options provide the best economic value to possible customers. The other major concerns with the introduction of 42-V power systems are phys-ical and practical viability aspects, such as arc faults and ensuing fire hazards. These and various other practical issues are dis-cussed in the following section. 1) Practical Issues Related to 42-V Automotive Power Sys-tems: As is apparent, by increasing the present 14-V network to 42-V, significant component and system changes within the vehicle will be necessitated. One of the major motives for this change is because of the nature of faults and their subsequent consequences, due to the higher current carrying wires in a 42-V automotive power system environment. It is obvious that the ten-dency is to produce longer arc faults, which have to be addressed to provide automotive safety. Wires that are semi-cut or scraped, in all probability, cause longer arc faults at higher system volt-ages. Furthermore, various research issues also arise from the point of view of vehicular power electronics and motor drives. For example, by reducing the mild HEV power system operating voltage (from 150 V/300 V to 42 V), the required current to pro-vide the necessary power increases. Thus, this corresponds to the entire winding of the electric traction machine to be restruc-tured. Issues such as heat transfer and protection also require a detailed investigation before the 42-V architecture becomes practicable in the auto industry. On the other hand, power electronic switches in 42-V sys-tems may be required to handle RMS currents in the proximity of about 400 to 500 amps/phase [29]. Currently, in order to switch such high profile currents, parallel-operated power electronic switches are being proposed, since using single-level switches is highly uneconomical. Recently, advanced MOSFET switches have been introduced for use with prototype 42-V automotive power systems. Trench IGBTs have also made noteworthy progress from the point of view of providing 42-V architectural solutions, wherein the research focus is mainly on solving reliability and short-circuit current capability issues. D. Power Electronics Solutions for HEVs Power electronics is an enabling technology for next genera-tion of vehicles, which should be cleaner, smarter, more precise, more efficient, and more flexible. In the past decades, power electronic devices were avoided mainly because of their cost issues. The reasons for increased interest in automotive power electronics can be separated into the ensuing sections. 1) New Architectures: By increasing new electrical loads, cost and complexity of the system is on the increase. Such archi-tectures need new switching and reliability features. Power elec-tronics makes the possibility of integrating switching and fusing functions into one component with higher reliability. Possibility of implementing different control methods on power electronic systems is another reason to go away from relay switching. Also, by implementing integrated sensing techniques in power elec-tronic devices, diagnosis and fault detection becomes easier to implement. Furthermore, development of clean and energy effi-cient vehicles in future vehicle technologies such as EVs, HEVs, 573 and FCVs is not possible without implementing new architec-tures, which are available using power electronics. 2) Power Conversion on Demand: Most of the auxiliary drives in vehicles are designed for worst-case scenarios. Power electronics and motor drive topologies make it easier to have higher efficiency by providing adjustable speed drives. Es-pecially, engine-cooling fans have been designed recently, implementing power electronic controls and adjustable speed drives. 3) Voltage Conversion on Demand: Different components in vehicles need different levels of voltages. Different voltage levels in dual-voltage architecture are available using power electronic converters. Induction or synchronous machines need ac voltages with high power for propulsion, and small motors for fans and pumps require ac voltage with low power [30], [31]. Converting dc-to-ac voltages and dc-to-dc voltages with different voltage levels is not possible without using power elec-tronic converters. 4) Precise Electronic Control: Engine controls such as igni-tion or fuel injection need precise timing and dynamic control of actuators. Fuel injectors should work on very high pressure with more precise opening time. Engine developers are working on systems to replace the camshaft with electronically controlled variable valves, promising up to 25% more fuel economy. These controls cannot be imagined without the use of power elec-tronics. 5.