FR0105764

ELECTRIC VEHICLES, HYBRID ELECTRIC VEHICLES AND FUEL CELL ELECTRIC VEHICLES : WHAT IN THE FUTURE

Prof. Dr. Ir. G. Maggetto, Ir. J. Van Mierlo Vrije Universiteit Brussel e-mail: [email protected] . [email protected]

1. INTRODUCTION

In urban area, due to their beneficial effect on environment, electric vehicles, hybrid electric vehicles and fuel cell electric vehicles are an important factor for improvement of traffic and more particular for a healthier environment. We are quite rapidly reaching the end of the cheap oil era [1], This could happen around 2010 and is nowadays probably indicated by the steadily growing oil price. Therefore the need for alternative energy source is growing and the price competition of alternatives against oil is becoming Fig. 2: Two or four motor drive for electric vehicles more and more realistic. Electric vehicles, hybrid electric vehicles and fuel cell electric vehicles are 3. STRUCTURE OF HYBRID ELECTRIC offering the best possibility for the use of new energy VEHICLES AND FUEL CELL ELECTRIC sources, because electricity can result from a VEHICLES transformation with high efficiency of these sources and is always used with the highest possible efficiency The implementing range of an electric vehicle can be in systems with electric drives or components. Some extended by an additional energy transforming system, basic considerations about the situation today and in a i.e. an internal combustion motor/generator group or mid and long-term perspective, are presented together fuel cell. For the sake of simplicity the vehicle will be with the infrastructure developments [2], named hybrid electric vehicle (HEV) and fuel cells electric vehicle (FCEV). Two main structures are 2. STRUCTURE OF PURE ELECTRIC defined in hybrid electric vehicles: series hybrid and VEHICLES parallel hybrid.

The electric drive system consists in the simplest case of battery (1), converter (2), motor (3), changeable or fixed gear (4) and differential gear (5) (fig. 1)[3], Besides the torque splitting with assistance of the differential gear, a two (or four) motor propulsion (3) is also possible (fig. 2)[4,5], The motors are placed in the wheelhubs. But in this case, each motor needs a separate converter (2) with speed and torque control, which guarantees the necessary torque splitting in each condition. A superposed slip-control is possible. The advantage of a wheelhub motorization relies in the ease to realise a four wheel drive system but mainly for Fig. 3: Series hybrid buses in the design of low floor solutions. The series hybrid (fig. 3) is a combination of energy sources. The traction is obtained by only one central electric motor or by wheelhub motors. The on-board total energy source results from the combination of two or more energy sources. Hence a decoupling of the operation of the energy source from the required traction power is possible. The rated power of the engine-generator group can be designed on very different ways depending on the applications Fig. 1: One motor drive for electric vehicles characteristics. The fuel cell hybrid structure (fig. 4) is a series structure in which the engine/generator group is replaced by a fuel cell system producing electric energy starting from stored hydrogen or from a fuel tank feeding a reformer to produce hydrogen.

Fig. 6: Series hybrid with peak power unit

A combined hybrid (fig. 7) is a combination of a series and a parallel hybrid drivetrain. By adding a Fig. 4: Fuel cell hybrid mechanical connection in a series hybrid between the internal combustion engine and the electric motor a The excess of electricity produced by the fuel cell can combination of series and parallel hybrid working be stored in a buffer battery. When the battery is left mode can be realised. This solution allows benefiting out one has no longer a hybrid vehicle but a fuel cell from the parallel as well as from the series hybrid electric vehicle. concepts. Thermal engines are usually petrol or diesel The series hybrid concept can also be chosen for a two motors. motor propulsion, four motor or multi-motor propulsion in the same way as for pure electric vehicles.

Fig. 7: Combined hybrid Fig. 5: Parallel hybrid Hybrid drive systems need a good power source. The parallel hybrid (fig. 5) is a combination of traction Normal traction batteries are not suitable for hybrids. systems. A combination of electric machines and The energy management systems of all hybrid internal combustion engine, being part of two or more structures will play a fundamental role because of its driveshafrs, perform the traction. Each driveshafr has influence on the global energy efficiency and the to be associated with an energy source. The parallel emissions. Therefore a good data acquisition and hybrid drives realise a purely mechanical power control system becomes a key element of the drive addition. Clutches can disconnect each motor. This structure. way, it is possible to drive only with the electric motor, only with the internal combustion engine, with both 4. PERFORMANCES OF ELECTRIC VEHICLES motors or with the internal combustion engine driving only the electric machine to charge the battery. An electric vehicle has to fulfil all demands of the Solutions with completely disconnected motors driving urban and suburban traffic. These demands are each one axle are called dual mode hybrids. different and depending on the vehicle kind and size. It is not possible to assess and conduct evaluations on All topologies different from the series and parallel one type of vehicle and utilisation pattern representing hybrid electric vehicle shall be called complex hybrid all together the different segments of the automobile vehicles. Hence complex hybrid vehicles include series population. The different market segments can be: hybrid with peak power units (fig. 6), parallel hybrids small passenger cars or second family car, the family with flywheel mechanically connected via e.g. a car or intermediate car segment, high class segment, continuous variable transmission (CVT) or combined commercial delivery vans, trucks, minibuses and urban hybrid vehicles. buses; but also electric bicycles and scooters.

126 Piles a combustible et interfaces pour les transports Generally the maximum and continuous velocity, electric drive: the bigger the vehicle, the smaller are the gradeability, acceleration and range describe the specifications like tractive force, torque power and vehicle characteristics. continuous speed. The driving range of a pure electric vehicle is defined In the past, these specifications did not show such high by the battery energy content. The wished continuous values everywhere in the world. Often, low speed (60 - speed on a flat road is used to design the battery and 70km/h) and low gradeability (15 - 20%) made the EV the components of the drive system for the continuous not comparable to petrol or diesel driven vehicles in or one hour power rating. city and highway traffic. Regenerative braking is a main feature of electric Table 1 shows vehicles characteristics realisable with vehicles. For this a sufficient high enough brake torque short-term or even today’s most performant batteries. and battery recharging current must be available to The most popular solutions on the today’s European fulfil the requirements. market are the cars (106 and Saxo) and the vans Fig. 8 shows the “throttle ” pedal characteristics of an (Partner and Berlingo) of the PSA group. electric vehicle. passenger van minibus urban car bus

M olor tor que range 120-250 100-150 140-200 150-300 Maximum torque [km] Full th rottle max. speed 100-120 Part ia 1 80-100 80 70 - throttle [km/h] Regenerative braking Motor speed continuous 100 80 60 60 speed [km/h] Fig.8: Driving torque curve. grade 30 20-25 15-20 12-15 The driveability is very important, which requires a ability high starting torque at standstill, a quick and stable [%] response of the motor and an efficient controllable regenerative braking. To have a smooth gentle start the acceleration 7-10 10-15 12-18 15-20 rate of power increase of the motor should be limited. 0 to 50km/h A tractive effort - vehicle speed diagram [2], directly [s] derivable from the motor torque-speed characteristics, is the main characteristic for a vehicle drive. For a Table 1: Present reachable goals for electric better comparison between passenger car, van, minibus vehicles. and urban bus the tractive effort is referred to a vehicle mass of one ton. 5. PERFORMANCES OF HYBRID ELECTRIC VEHICLES

5.1 Rate of hybridisation

Some definitions are given to better understand the hybrid concepts.

5.1.1 Order of Hybridisation

The order of a hybrid system is the number of different systems necessary to build the drivetrain [6]. a passenger car b van c minibus d urban bus In the case of an electric or thermal vehicle there is Fig. 9: Tractive effort diagram for electric vehicles only one motor or engine driving the vehicle. These drivetrains are from the first order. Also fuel cell Fig. 9 shows also the minimum power per mass for vehicles without a battery are first order systems. different types of electric vehicles. Furthermore, the A parallel hybrid built up with one engine and one diagram shows basic differences in the design of an motor is a second order hybridisation as well as a series

Piles a combustible et interfaces pour les transports 127 hybrid electric vehicle containing a battery and another energy source. 1 Thermal Vehicle - "V. OIU/* When a peak power unit, like a flywheel or super­ Aker na tor-starter j I capacitor, is added to the drivetrain, the vehicle is from Parallel hybrid ,<^ RojT> the third order. All complex hybrid drivetrains are J third or higher order systems. , » Electric Vehicle Ik \ A combined hybrid drivetrain (fig. 7) can also be seen Ranee extender as a third order hybridisation. Although there are only two energy sources, there are three shafts: one Series hybrid yc Rotf> 3 I connected to the engine, one to the generator and one to the electric motor. All three are mechanically i No-battery Electric Vehicle in connected to the wheels.

5.1.2 Electric Hybridisation Rate (HER) Fig. 10: Different hybrid electric vehicles classification. The Electric Hybridisation Rate (EHR) gives an indication of the performance, and above all, the range Looking at fig. 10 from top to bottom, we see, first, the in protected areas. This means the ‘more battery ’ the thermal powered vehicles, the family of parallel longer one can drive without generator or engine, the hybrids, the electric vehicle, the family of series hybrid, higher the electric hybridisation rate. It is the ratio ending with the fuel cell or the so-called diesel-electric between the electric power and the total traction power transmission structure. and is expressed as a percentage. The higher this rate, Back at the top, the starting point is the thermal engine the more the vehicle tends to a pure electric. in its classical structure. It assumes that no battery is present onboard these vehicles, with the auxiliary 5.1.3 Combustion Hybridisation Rate (CHR) battery not taken into account. The first step to hybridisation is in the parallel hybrid To have an idea of the relative contribution of the group and is represented by the “Alternator-starter” internal combustion engine a complementary definition solution integrating the charging alternator and the to the Electric Hybridisation Rate can be introduced: electric starter motor in the motor flywheel. With an Combustion Hybridisation Rate (CHR). It is the ratio increase in size (power and energy) of the auxiliary between the thermal power or fuel cell power and the battery, recuperative braking becomes possible. total traction power expressed as a percentage. The Going further down, we observe an increase in the higher the rate, the more the vehicle tends to a pure power of the battery as well as the electric motor’s thermal or fuel cell vehicle. power while the power of the ICE is decreasing. If pure electric range is desired, the increase in power of 5.1.4 Rate of Hybridisation (RoH) the battery has to be complemented with an increase of accumulated energy, consequently an increase of The Electric Hybridisation Rate or the Combustion weight. Hybridisation Rate don’t express the degree of We can more or less locate the PRIUS solution in this hybridisation itself, but rather how much a vehicle group with a rate of hybridisation (RoH) of 33 kWel/53 leans against the electric vehicle side or respectively to kWth = 0,62 (or 62 %). The thermal motor power is the thermal vehicle side. still dominant. The Rate of Hybridisation (RoH) describes the relative Still further down, we see the increase in the electric contribution of each energy source (in the case of series motor’s power, and power of the battery, whilst there is hybrid electric vehicles) or traction system (in the case a decrease in the thermal motor’s power. At the bottom of parallel hybrids). of the parallel hybrid block we naturally meet the pure electric vehicle solution. Going further down, we enter 5.1.5 Classification the family of series hybrid drive systems which is characterised by a full electric motor traction system. Armed with these definitions a diagram representing a The first step indicated is the so-called “range extender panorama of second order hybrids can be constructed solution”. This small thermal motor-electric generator (fig. 10). This user-friendly diagram is based on group is providing complementary energy to the battery reference [6] and is pointing out the different or traction system, thereby extending the battery possibilities of hybridisation in terms of power by vehicle range. ■ varying progressively the electric and combustion Further increasing the ratio of thermal power to battery hybridisation rate. power, we reach a structure without a battery and with It is possible to show which continuum exists in the 100% electric power generated by a thermal engine- global field. electric generator group.

Piles a combustible et interfaces pour les transports 128 This is the so-called “diesel-electric” transmission -electrolysis of water with electricity produced by wind system. or solar energy; To the series hybrid block naturally belongs the fuel -reforming of methane (natural gas - CH4 ), methanol cell hybrid structure with a power partition between the (CH3OH) or other hydrocarbon fuels (e.g. those fuel cell and the battery. At the bottom the battery classically used today); disappears as we have a 100% fuel cell powered drive -reforming of ammonia (NH3). system. The global efficiency related to these different ways remains an open question as well as the necessity, or We see that the number of possible solutions is infinite not, to use a buffer battery. but not all will demonstrate the same value nor economically nor with respect to efficiency nor with Electric motor respect to emission and in the end nor with respect to a Two main ways seems to emerge. The asynchronous weighted mix of these criteria. To evaluate these (induction) motor has the advantage of its higher criteria a software has been developed at the ‘Vrije robustness. The permanent magnet motor leads to a Universiteit Brussel’ as a result of a fundamental PhD more expensive solution with a somewhat higher work which can be consulted at: efficiency. It is the solution to be implemented in case http.V/etecnts 1. vub. ac. be/VSP/ of integration of the motors into the wheels. Due to their low cost, reluctance motors can be a good 5.2 Component requirements choice in the lowest EHR field.

Nowadays the choice of the structure of an hybrid 5.3 Segmentation vehicle is a strong evaluating matter because of the more or less rapid but steady evolution of the To plan a suitable hybrid vehicle its usage must be components technology and performance. It is out of clearly defined first. One way of doing this is to use the scope of this paper to try to give an extensive the segmentation of the automobile market. The basic overview of the characteristics of all possible criteria is the price, which is justified by technical components for all possible configurations but some performance and equipment, but in the future the price among the most classical can be briefly discussed. of energy, the reduction of consumption and emissions will play an increasing role. The standard use per Batteries segment is very important for selecting, but also for Compared with the electric vehicles the batteries for defining the type of hybrid vehicle, as its price cannot hybrid vehicles are characterised by a reduced energy really be representative. contents and higher power requirements. A specific energy of at least 50 Wh/kg and a specific Second family car segment power ranging from lOOW/kg, continuous, up to The second (or third) family car segment, also 200 or 300 W/kg is a must for an efficient design. considered as "ladies" or "young persons" car is characterised by a frequent use in town, a relatively low Petrol-, diesel- and gas engine /Electric generator daily mileage and a great manoeuvrability in urban The maximum power of the thermal engine depends areas. Long trips are only occasionally performed, clearly from the rate of hybridisation. The acceleration therefore some reduced comfort is acceptable. Due to power is mainly delivered by the battery. For the the frequent use of the car in urban areas the use of the electric generator the tendency goes clearly towards the thermal engine in variable regime leads to a implementation of permanent magnet generators which dramatically loss of efficiency (even lower than 10 %). efficiency at constant power working point is between Therefore the series hybrid drivetrain with a rate of 90 and 95 %. hybridisation up to 20-30 % (CHR) seems to be a realistic approach despite the fact that in the series Fuel cells structure all losses (thermal engine or reformer, Fuel cells can replace the thermal engine/generator generator or fuel cell, converter, electric motor) are group. The associate hybrid structure is always the accumulated. The mileage in all electric mode could series one. Maximum efficiency around 60% can be be around 50 km. expected with which the efficiency of hydrogen Electric vehicles with a range extender unit (up to 300 production (e.g. the reformer) has to be multiplied. km with a NiCd battery and probably more with a The way to produce hydrogen considered today are Lithium-ion battery) fits fully in this segment. multiple: They could lead to the solution for all psychological -electrolysis of water in countries with hydro energy obstacles related to the acceptance of EV’s. (e.g. Canada, Norway) or nuclear power plants (e.g. France);

Piles a combustible et interfaces pour les transports 129 Intermediate car segment are to be compared with vans and lorries. The service The intermediate car population segment is a very of a bus on a public transportation line is clearly a versatile car used frequently in town, with a good road heavy duty service characterised by a big number of performance, often used as the main and even sole car. stops, acceleration and braking phases. Constant speed Long trips are performed regularly, therefore comfort is is becoming a rare event. taken into consideration. The series solution is once more the best solution here Therefore the competition for this segment between with a rate of hybridisation within the step 30-50 %. series and parallel solution will be high, the efficiency The most popular realisations on the European market of the parallel structure being better on long trips. It are the IVECO-ALTRA Europolis (7,2 m) and could be the field of combined hybrid structure as Cityclass (12 m) buses. implemented in the Toyota PRIUS which is on the Higher rates can be implemented (greater than 50 %) market now (EHR of 62%, 3.81/km in low duty service but in that case the working mode can dangerously up to 5.51/km in high duty service, in the CITELEC- approach the working mode of a pure diesel (thermal AVERE 2nd Transeuropean demonstration trip from motor) generator group with a strongly variable load Monaco to Hanover) and the field of the fuel cell car as and consequently a poor gain (if even existent) in implemented in the NECARIV, based on the Mercedes efficiency and emission level. Gain could exist if the class A car, which arrival on the market could happen efficiency of the mechanical transmission (gearbox, ...) within 5 to 10 years. demonstrates to be poor.

High class car segment Lorries and long range (tourism) buses The high class car population segment has excellent This is today the field of diesel motor where the latter road performance, high technical performance and top develops its best efficiency. Parallel hybrid structure comfort, is not at all adapted for town use and is often can be considered for city use. The fuel cell find here the first car of a family with several cars. In this case one of its best promising application. the parallel hybrid solution seems to be definitively the best one because of the long highway trips. The 6. BATTERIES AND OTHER ENERGY electric hybridisation rate could be around 35 %. This SOURCES class could also be a field of implementation of the fuel cells which is in fact a full electric solution. This type Energy for vehicles can be delivered from different of car is often used as a taxi, the series structure is then sources. Thermal energy from gas and fuel has to be more justified. converted into mechanical energy but this is done with low efficiency. Oxygen comes from the air, exhaust- Small delivery vehicles class gas is emitted into the air. Burned material cannot be The small delivery vehicles are used in a similar way as reactivated [7]. the second family car, the comfort is usually somewhat Electrochemical energy is stored in batteries or sacrificed to add additional practical facilities. The produced by fuel cells. The battery is the most series hybrid drive train with the same characteristics as important part in an electric vehicle. Energy density for the second family car segment is the realistic and power density are the first battery parameters to be approach for this case. The electric Renault Kangoo considered. equipped with a range extender using a 3 cylinder, 600 cc, ICE engine is a very promising realisation. This Table 2 shows the main characteristics of available and could be an ideal solution for postal and goods delivery advanced batteries for electric vehicles. services. The lead-acid battery is the best known. For maintenance-free batteries the electrolyte will be stored The citybus in a fleece material or in a gel [8], New types with The classification of the bus population is quite simpler bipolar cells are in tests. This battery is heavy but because of the specific use i.e. for urban public cheap. With a good battery management system the transport with the 6m, 9m, 12m and articulated lifecycle (500) can be secured. structure or for tourism. The performances for city The nickel-cadmium battery [9] has a high power public transport are quite modest if one refers to the density and a high cycle life. Completely sealed cells realisable medium speed in most cities, about 15 km/h, with gas recombination are in production. This battery but the range must reach 250 km and sufficient power is equipping most of the European electric vehicles on for acceleration and hill climbing is necessary. The the market. maximum speed will range between 60 and 80 km/h. In nickel-metal-hydride batteries an alloy storing The increased weight imposed by the hybrid (and even hydrogen will be used for negative electrodes instead of electric) structure may have to be translated in a cadmium (Cd). Energy density and power density reduced number of passengers i.e. in a reduction of increase compared to the NiCd battery [10]. exploitation capacity. The tourism or long range buses

Piles a combustible et interfaces pour les transports 130 Pb-Pb0 2 Ni-Cd Ni-MH Na-NiCl Li-Ion Working 0-45 0-50 -40 - 50 300-350 -40 - 60 Temperature (-20- 60) (-40- 60) (250-370) °C Specific Energy 161 236 300 794 275 Wh/kg Specific Energy 20-30 40-55 50-60 80- 100 90-140 (2 h discharge) Wh/kg Energy density 60-80 60-90 100-150 110- 120 150-200 Wh/1 Specific Power 75 - 100 120-150 140-200 150-200 350 - 400 W/kg 500-1000 (for hybrids)

Cell voltage 2,1 1,35 1,35 2,58 3,6

V,/V (charged)

Lifecycle 500 2000 1000 1000 1000

Table 2: Characteristics of batteries for electric vehicles

The sodium-nickel chloride battery is a hot battery. advanced development in the field is realised by Its controlled working temperature (270°C) eliminates Daimler Chrysler with a Ballard fuel cell. any influence of outside temperature. This battery The fuel cells need hydrogen as basic fuel. The demonstrates very good applicability for EV’s [11,12] production of hydrogen by means of a reformer for and HEV’s in daily fleet service. It is known as the methanol (or another type of hydrocarbon fuel) could ZEBRA battery. solve the problem of fuel infrastructure, which could An advanced battery is the lithium-ion battery [13]. then remain practically unchanged. The marketing is Small cells are already strongly used in the portable also announced around 2004 but this has only the value electronic market. Batteries for EV’s are under of a very optimistic market announcement in a field with development. A first prototype for an EV was shown at very hard competition. the 13th Electric Vehicles Symposium, Osaka 1996 and Developments of metal-air batteries like zinc-air or prototypes demonstrations (Peugeot 106 and Ford Ka) aluminium-air were started in the mid sixties. Since have got a range of more than 200km in the Michelin few years Electric Fuel Ltd., a company in Jerusalem, ‘Bibendum Chalenge 2000’. The real marketing is now Israel, and an institute in Karlsruhe, Germany, announced around 2004. developed new zinc-air batteries [14]. Zinc-air is now The development of fuel cells goes back in the last abandoned in Germany but efforts are still developed in century, with the invention by GROVE (UK). It was Italy by the EDISON company. stimulated by the wish to produce energy independently Energy can be stored also in a flywheel. The from the Carnot law. The alkaline fuel cell was mechanical energy is transformed into electric energy by developed in Europe and mainly used for space a generator driven by the flywheel. In some application exploration and satellite. The power density of proton the flywheel-generator set can be a booster for high exchange membrane fuel cells (PEM) is significantly power. higher than that of alkaline fuel cells and the PEM is Still in development are supercapacitors, which also able to work at ambient temperature. Most of the car can be used as short time power source. companies are developing big efforts to integrate the PEM fuel cells in a small part of the car body. The most

Piles a combustible et interfaces pour les transports 131 7. TRACTION MOTORS Regenerative braking or reverse driving is performed by the converter control unit without any additional Table 3 gives a comparison of different motor types: switches [18,19]. Compared with DC chopper circuits asynchronous motor (ASM), permanent magnet motors with relatively low frequency, inverters need a big filter (PM), switched reluctance motor (SRM), direct current capacitor to reduce the current pulses in the battery. motor (DCM) and synchronous motor (SYM). Motors To provide 12 V auxiliary power and to charge the should always be evaluated in function of the needs of auxiliary battery during operation, a DC/DC converter is the application. E.g. each of the different motors can be necessary. In the most cases DC/DC converters are less efficient than the others in some regions of made with single-ended forward converter or with push operation, and it can be more efficient than the others is pull forward converter. In some new development some other regions. To make a good comparison, one flyback converter with very high frequencies are used. must not compare maximum efficiencies, but relate the efficiency map to a certain speed cycle. The table 9. CHARGERS AND CHARGING shows an advantage for the permanent magnet motor as INFRASTRUCTURE FOR EV’S AND HEV’S traction motor for electric vehicles. Indeed, on the level of performance the permanent magnet motor has a lot of Electric vehicles batteries need to be recharged. For interesting features. But considering the production hybrid vehicles the situation can be quite different cost, one must take into account the high price of the depending on the structure of the drive system. Indeed magnets and the more complex construction of the for the diesel structure (without battery) and for the motor. Regarding the price, the global result will combined hybrid structure used in the Toyota PRIUS no probably be in the advantage of the asynchronous motor external charging is required. The basis question but in the last published information and development discussed by associations promoting EV’s and HEV’s programmes, the switched reluctance motor is earning a is: “Is it more efficient or is it necessary to recharge the lot of interest. battery of an HEV at the mains to get the best results with respect to energy consumption and emission?”. ASM PM SRM DCM SYM The debate is still open but the answer can be a matter Motor size 0 + 0 - 0 of economy and/or infrastructure. mass Electric vehicles are largely independent of the charging

High speed + + + - - place if they are equipped with an on-board charger Endurance + 0 + - - connectable with any AC outlet. A 230V/16A outlet can maintenance supply an apparent power of more than 3.5kVA. Such Efficiency 0 + 0 - 0 an outlet can be installed everywhere e.g. in public Controller 0 0 0 + 0 parking or in home garages. A battery of 15kWh can be size charged in less than five hours (main charging) with a mass charger having a unity power factor [20,21], Electric Controllability + + - + 0 utilities in Europe are nowadays demanding more and Number 0 0 + + 0 more consumers with low distortion and reactive power power devices requirements. From the AC power supply system a Reliability 0 0 0 0 0 quasi sinusoidal current with a low harmonic content, at TOTAL +++ ++++ ++ - - — unity power factor, can easily be obtained. In Europe, three-phase feeding is used for powers higher Table 3: Comparison of different motor types. than 3.5kW. This is a line normally separated from the usual AC single-phase distribution. Even considering that most electric vehicles can be 8. POWER ELECTRONIC FOR EV AND HEV charged at home garages, the provision of public DRIVES charging stations is a necessity as it is for the refuelling stations for classical vehicles. Thanks to power electronics and microprocessor based In countries like France, Germany, Italy, Switzerland, control devices the performances and control of all the United Kingdom and Finland on street charging stations traction systems used in road transportation sector is becoming more and more efficient. From today's view, have been developed. The cost of the energy used the IGBT will be the common switching device for during charging is much lower than normal downtown EV’s. Only converters for low battery voltages (< parking fees and could easily be include in this fee. 100V) and converters with very high frequencies The development of on street charging infrastructure (DC/DC converter, charger) will be equipped with must be done with a particular emphasis on safety MOS-FETs [15,16,17], aspects and standardisation. Today’s inverters for electric vehicles will be designed Half fast (7-10 kW) and fast charging station (25kW and with modules of bipolar transistors, MOS-FETs or more) can help creating confidence in the use of electric IGBTs. Three-phase frill bridges modules are available vehicles. They allow recharching in less than two hours at reasonable prices. The inverter control-unit has to or in a few minutes or some ten to twenty minutes generate the three-phase voltage. eliminating so the fear to fall with an empty battery.

132 Piles a combustible et interfaces pour les transports The only charging infrastructure used up till now in cumbersome operation taking into account the heavy Europe is of the conductive type i.e. with a galvanic weight of the batteries. Opportunity charging is much connection with the mains. In USA and Japan inductive easier, and when it can be inductively done, without charging systems have been developed and are cables or plugs, offers the most attractive solution. becoming popular. The present state of the art of inductive charging system The basic idea of the inductive system is quite shows several approaches, which related to the use of straightforward: the main transformer of the battery the working frequency (50 Hz, 400 Hz or more then 20 charger is split in two parts. The primary is mounted kHz), have led or may lead to industrial developments. fixed on the ground, the secondary is mounted on the For all the above mentioned application the basic vehicle. It will now be sufficient to place the primary charging power level is 3 kW but a half fast charging adjacent to the secondary to "re-assemble" the procedure with 6 to 10 kW power level is very easy to transformer and to allow energy transfer from the grid to implement. The electric power levels used in buses are the battery. higher of course. The proposed technology is however Due to its particular characteristics of user-friendliness fully suitable for power levels up to 100 kW. and safety, inductive charging is well suited to a large number of electric vehicle applications. Because of the 10. FUELING INFRASTRUCTURE infrastructure needed, it seems likely that in a first period fleet applications will be the most important. To The way towards hybrid and fuel cell hybrid vehicles make an automatic rent-a-car system attractive and will very probably be accompanied by a fundamental successful, it must be reliable, safe and easy to use. The change of the fueling infrastructure. Indeed, as stated in manipulations to be done by the driver should be as the introduction, today there is general concern about simple as possible: ideally, only identifying himself to the increase in oil prices and it is generally agreed that the system (e.g. with a credit card), board the vehicle the era of cheap oil is nearing its end. and drive away (the credit card could serve as “ignition Do we have alternative energy sources to compensate key”). Any additional activities, such as unplugging and for this situation and allow the further development, or storing a cable,... are clearly unwanted. In this indeed further maintain the mobility capacity in the viewpoint, inductive charging systems are particularly world? The number of alternatives is quite large but attractive for this applications. each has its own limitations. City centres are the usual operation theatres for taxi fleets, which makes them particularly attractive for LPG is cleaner but is a by-product of oil distillation and electric traction. The daily mileage of taxis in big cities accounts for only a complementary ten percent of fuels however can be quite important (150-200 km) and may produced for transport. The distribution infrastructure exceed the range of a typical electric vehicle. for LPG is, due to the liquid form of this gas under This problem may be countered through the use of pressure, quite easy to install and is already opportunity charging, which can easily be implemented implemented. Most of the safety aspects have been taking into account that taxis usually spend an important solved. lot of time waiting at taxi ranks. Having to disconnect the charging cable takes some time however and will CNG shows big reserves but with a situation similar to make the electric cab less popular with the customer, that of oil, even if the delay is a bit longer, it is a which in most cases will be in a hurry. Inductive cable- questionable solution with respect to efficiency. The free charging is the solution. distribution infrastructure is generally associated with Commercial vehicles (i.e. light goods vehicles) are one the already existing one for domestic applications. CNG of the most obvious potential applications for electric need to be compressed up to 200 bars and this costs vehicles in urban areas. The ubiquitous British milk electric energy. In the slow fill procedure the filling floats are a well-known example; furthermore, advanced time accounts some hours as for the battery of an electric vehicles are used in a growing number of electric vehicle. The quick fill procedure requires a European cities for goods distribution and service heavier compressing installation with accumulation applications. The utilisation of inductive charging boosters. Recharging is possible in less than fifteen systems on such vehicles has obvious advantages. On minutes. This solution is acceptable for fleets one hand, the operations to initiate charging become particularly for bus fleets as popular in Northern Italy much more simple and user-friendly, which is (Ravenna) particularly interesting when frequent charging intervals are used (opportunity charging). On the other hand, the Bio fuels has the problem of costs and efficiency at the simplicity of the charging operation will ease the level of production. The distribution infrastructure is acceptance of the system by the personnel. very similar to that of the classical hydrocarbon fuels but Electric buses offer a quiet and fully emission-free raises more problems of safety in the case of methanol public transport in city centres. The daily mileage of a (bums without light production, more corrosive, typical city bus however usually exceeds the range of an dissolution in water table in case of leak). electric vehicle on a single battery charge. Battery exchange is a potential solution, but can be a

Piles a combustible et interfaces pour les transports 133 Hydrogen is considered today as a major solution for 12. EUROPEAN PROGRAMMES the future but its production, distribution and its global efficiency remain an open question. Distribution under A number of RTD actions are running in the ending gaseous or liquid form has practically to be totally fourth framework programme, JOULE-THERMIE and solved, despite the existence of some industrial BR1TE EURAM. They are devoted to the development distribution networks for gaseous hydrogen. Once more of batteries (Li), the testing of batteries (Pb, NiCd, this could be easily organised for fleets in association NMH, Li-ion, Li-Polymer), the testing of EV or HEV with a local production of hydrogen. A demonstration fleets (ZEUS, JUPITER, SAGITTAIRE, EVD-POST, of a fuel cells bus fleet in ten European cities will ELCIDIS, ...). probably evaluate solutions in this way. The case of Important integrated RTD efforts for hybrid and fuel productions of hydrogen by reforming a “classical” fuel cells vehicles are further supported in the now running (methane, methanol, hydrocarbon fuel, etc. ...) leads the fifth framework programme (PRAZE, E-TOUR, distribution infrastructure back to the problems ENIGMATIC, ELEDRIVE, FUIENAV,...). mentioned above. This way seems to attract the biggest attention of the classical energy providers in the field of 13. CONCLUSION road transportation. EV, HEV and FCEV are an existing technology but Electricity is probably the cleanest and most efficient many efforts are still to be developed to put valuable energy source to use but it is a secondary energy source products on the market. The demand of research and has to be produced using the others. Opposite to the development and design effort in the field of drives, traditional centralised production, decentralised energy sources and charging infrastructure is becoming production is becoming popular (e.g. solar photo voltaic enormous and a challenging field for the European plants, windmills, combined heat and electricity Community. production, fuel cell power plants). Installation of a general or a local network is very easy. The future of the access to energy, the environmental and climate problems and the need to solve the mobility Consequently, the path from primary energy to the problems in the cities are all fields in which electric, wheel is generally a multi-stepped one and raises the hybrid and fuel cells vehicles offer a large pattern of question of balance between emissions, efficiency, interesting and necessary solutions. access to energy source and economy. Considering the future’s needs, it is clear that the solution is not a unique one but a mix of different ones.

11. THE MARKET

In collaboration with the European Union RTD Programs, studies have been performed (1994-1996) about the opportunities for electric and hybrid vehicle introduction in European cities. The selection of these cities takes into account the commitment towards electric transport of each city on one hand and the choice of a "palette" of cities with different characteristics on the other hand. This way, it has been possible to give a thorough description of the main activity and policy domains where electric and hybrid vehicles could be used in Europe. These studies have confirmed the results obtained in the COST 302 study [22], in the EDS study for the European Parliament [23] and in the inquiries performed by CITELEC among its members. The studies all concluded in a market between 10 to 30 % for EV and even 70% in city administration fleets as defined by AVERE France in a recent inquiry. The Californian market defined for 2003 provides 10 % for EV, 25 % for ULEV i.e. HEV and the rest for LEV (low emission vehicles). The Californian mandate has been recently confirmed. But the real future will probably be a mix of EV’s, hybrid ULEV and fuel cells vehicles. The time needed for this will last 10 to 20 years.

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