Comparative Study of Alternative Energy Vehicles

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recharge from the wall socket. This paper describes ... electric vehicle, Plug-in hybrid electric vehicle,. Fuel cell ... Power from AC mains supply is used to charge.
Proceedings of the National Conference on Power, Instrumentation, Energy and Control (πCON-2011) Organized by Electrical Engineering Department, AMU, Aligarh 12-13 Feb 2011.

Comparative Study of Alternative Energy Vehicles: State of the Art Review #

Farhad Ilahi Bakhsh, *Mohammad Saad Alam Department of Electrical Engineering, Z.H.C.E.T, Aligarh Muslim University, Aligarh, India * Department of Electrical and Computer Engineering, Saginaw Valley State University, USA

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 Abstract-- With increasing concern over the environment and ever stringent emissions regulations, the alternative energy vehicles has been investigated as an alternative form of transportation. However, the electric vehicle suffers from relatively short range and long charging times and consequently has not become an acceptable solution to the automotive consumer. The addition of an internal combustion engine to extend the range of the electric vehicle is one method of exploiting the high efficiency and lack of emissions of the electric vehicle while retaining the range and convenient refueling times of a conventional gasoline powered vehicle. The term that describes this type of vehicle is a hybrid electric vehicle. Many configurations of hybrid electric vehicles have been designed and implemented, namely the series, parallel and power-split configurations. For further improvement Plug-in hybrid vehicles are introduced, these are battery dominant and have the ability to externally recharge from the wall socket. This paper describes comparative study of the alternative energy vehicles. Both components and control strategies are discussed. Finally the discussion will illustrate that an increasing degree of hybridization leads to higher overall vehicle efficiency, fuel and energy economy. Index Terms-- Alternate energy vehicles, Electric vehicle (EV), Fuel cell vehicle (FCV), Hybrid electric vehicle (HEV), Plug-in hybrid electric vehicle (PHEV), Organic fuel vehicle.

I. INTRODUCTION During the last few decades, there is an increased concern over the environmental impact of the petroleum-based transportation infrastructure, along with the specter of peak oil, has led to interest in an alternative energy transportation infrastructure. Major arguments justifying the development of alternate energy resources for transportation infrastructure are:  Local Zero emission legislation  CO2 reduction target  Fuel availability: usage of alternative fuel The alternate energy resources used in transportation infrastructure are called as alternate energy vehicle. It includes Electric vehicle, Hybrid electric vehicle, Plug-in hybrid electric vehicle, Fuel cell vehicle and Organic fuel cell vehicle. The electric vehicle concept is not new; it has been around since the early years of the automotive industry. In fact, until 1910 electric vehicles were more numerous than vehicles equipped with internal combustion engines. New environmental concerns over the amount of pollutants spilled into the atmosphere each day by internal combustion engines (ICE) have become a powerful motivation for the use of electric vehicles once again. Additionally, while the thermal efficiency of an internal combustion engine can only be 40% at best, electric motors, drawing energy from batteries, can operate with a peak efficiency of up to 90%. Also electric vehicles can recapture wasted energy through regenerative braking [1]. The greatest shortcomings of the electric vehicle in today’s busy world are unfortunately, it’s rather short range and hours of battery charging times. The gasoline engine dominates in range

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because of the high energy density of liquid hydrocarbon fuels, and dominates in charging times because a fill-up at a gasoline station takes minutes in contrast to hours of battery charging time. Because the electric vehicle (EV) cannot as yet match the conventional car in these areas, there has been limited EV production so far. Coupling a small internal combustion engine as an auxiliary power unit (APU) to an EV is one way to overcome the EV’s shortcomings [2]. Since the early 1900’s automobile researchers have suggested adding small gasoline engines to electric powered vehicles. In earlier years, accomplishing that goal was difficult because the technology needed to make such a concept practical was not fully developed. Today, however, with modern batteries, advanced electric motor and gasoline engine technology, and modern electronics for control of such complicated systems, the hybrid electric vehicle concept has become viable.

II. STATE OF THE ART REVIEW A. Electric Vehicle A vehicle, which is powered by stored electrical energy, is called an Electric Vehicle. If the storage medium is battery then it is called as Battery Electric vehicles include electric cars, electric trains, electric lorries, electric aero planes, electric boats, electric motorcycles and scooters and electric spacecraft. To drive this electric vehicle a suitable electric motor is used as a prime mover. To control this electric motor an electronic controller is used. A battery bank is used to store the electrical energy which is placed along with the vehicle. The battery operated electric vehicle is parked for 3 to 5 hours for charging the battery pack [1]. A separate battery charger is provided which take the power from A.C. Mains. Then the charged battery pack is used to drive the motor, which is controlled by a suitable motor controller. The electric motor develops the required tractive effort. The battery bank, controller and motor must have excellent efficiency, adequate capacity and low weight along with regenerative compatibility i.e. their ability to recover energy normally lost during braking as

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electricity to be restored to the on-board battery. Conventional DC motors are highly efficient and their characteristics features make them suitable for electric vehicles. Commutator and brushes are main components of D.C. motors. Maintenance and replacement of brushes at regular intervals is only difficulty associated with use of D.C. motors. The ac machines like induction motors and brushless permanent magnet motors do not have brushes and their rotors are robust because commutator and/or rings do not exist. That means very low maintenance. This also increases the power-to-weight ratio and the efficiency. Therefore new trend is to use brushless DC motor; vector controlled three phase induction motor and doubly fed induction motor [14]. To control this electric motor an electronic controller is used. A battery bank is used to store the electrical energy which is placed along with the vehicle. Power from AC mains supply is used to charge the specially manufactured heavy-duty batteries. There are special arrangements to charge these batteries, either by regular power charger, which will take 8 to 10 Hours to charge these batteries or by the fast charger, which can be used to charge the battery within 3 to 5 Hours. Then there is power controller which controls the power supplied to the motor. A separate 12 V battery is also provided to supply the power to the auxiliaries and peripherals. Auxiliaries include the micro controllers and other vehicle monitoring units. Vehicle monitoring unit monitors the control of acceleration, breaking system, battery charging, its state of charge and discharge etc. To operate the machines, equipments and peripherals at safe working temperature air/liquid cooling system is also provided. The specialty of these vehicles is that they can be operated as zero emission vehicles. Electric vehicle is a complex assembly that includes various parts like Mechanical, Electrical, Control, Magnetic, Pneumatic, Electrochemical, Thermal and Hydraulic etc.

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Fig.1 Electric Vehicle components [1]

Comparison The comparison between electric vehicles and I.C. Engine driven vehicles (conventional vehicles) is given as: TABLE 1 COMPARISON BETWEEN ELECTIRC VEHICLE AND CONVENSIONAL VEHICLE

Feature

Prime mover

Battery Electric vehicles

I.C. Engine vehicles

Electric motor

I.C. engine

Low as compared to EV

Power Transmission

Charged battery, ultra capacitors High due to battery bank Both mechanical as well as electrical

Braking system

Regenerative braking

Friction braking

Powered by Self weight

Diesel, Petrol

Mechanical only

Efficiency

High

Low

Eco friendly

Yes

No

Initial cost

High

Average

Running cost

Low

Very high

Electric vehicle have some disadvantages such as increased weight, limited range and limited recharging sites. Fuel cell vehicles provide the benefits of electric vehicle while eliminating their disadvantages such as limited range and recharging [3]. B. Fuel Cell Vehicle A Fuel Cell Vehicle (FCV) is an electric vehicle

that uses hydrogen rather than a battery to provide electricity that powers the motors at the wheels. Fuel cell (FC) is an electricity producing system that directly converts the energy stored in a fuel into electrical energy to power an electric motor without undergoing a process of combustion. Due to its attractive properties of potentially high efficiency particularly at partial load and producing no pollutants, the fuel cell system is considered to be an ideal power source for automobiles [4]. It is similar to a battery in that it may be recharged while it is being used to generate power. Instead of recharging by using electricity, a fuel cell uses hydrogen and oxygen. While a battery must be recharged after all its fuel has reacted; a fuel cell is a “refillable battery”. FCV can be twice as efficient as similarly sized conventional vehicles. They can also be equipped with other advanced technologies to increase efficiency; such as regenerative braking systems that capture the energy lost during braking and store it in battery. A fuel cell is an electrochemical device that produces electricity by separating the fuel (generally hydrogen gas) via a catalyst. The protons flow through a membrane and combine with oxygen to form water-again with the help of a catalyst. The electrons flow from the anode to the cathode to create electricity. As long as the reactants—pure hydrogen and oxygen—are supplied to the fuel cell, it will produce electrical energy. The only exhaust a fuel cell produces is water, so clean its fit to drink. A fuel cell system consists of one or more fuel cell stacks. Each stack is comprised of multiple cells in the same way that a battery consists of multiple cells [5].

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Fig. 2. Components of Fuel Cell vehicle [6]

FCV look like conventional vehicles from the outside, but inside they contain technologically advanced components not found on today's vehicles [6]. The most obvious difference is the fuel cell stack that converts hydrogen gas stored onboard with oxygen from the air into electricity to drive the electric motor that propels the vehicle. Fuel cell stack is the heart of a FCV [7]. The major components of a typical FCV are illustrated below. Hydrogen Storage Tank: Stores hydrogen gas compressed at extremely high pressure to increase driving range. Fuel Cell Stacks: Converts hydrogen gas and oxygen into electricity to power the electric motor. Power Control Unit: Governs the flow of electricity. Electric Motor: Propels the vehicle much more quietly, smoothly and efficiently than an internal combustion engine and requires less maintenance. High-output Battery: Stores energy generated from regenerative braking and provides supplemental power to the electric motor. Hydrogen is supplied to the fuel cell stack from the high pressure tank by way of a regulator. In order to improve the performance of the fuel cell any surplus hydrogen remaining after the fuel cell reaction is returned to the supply side of the fuel cell by the circulating pump. Air is pressurized by the compressor, after which it is pumped to the stack through the humidifier. The humidifier takes water vapor from the exhaust air from the stack and uses it to humidify the incoming compressed air. The pump circulates coolant between the stack

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and radiator. All major car manufacturers such as Ford, Honda etc are working on fuel cell concepts; several prototype vehicles have already been demonstrated. But the problems of hydrogen distribution plus onboard storage are huge. Best estimates are that it will take another eight years before fuel cell cars can be produced and sold at a reasonable price. However a fuel cell alone powered vehicle bears some disadvantages, such as heavy and bulk power unit caused by the low power density of the fuel cell system, long start-up time and slow power response. Therefore a fuel cell powered hybrid vehicle has been introduced. C. Hybrid Electric Vehicle A hybrid electric vehicle (HEV) is vehicle which combines a conventional internal combustion engine (ICE) propulsion system with an electric propulsion system. Hybrid-electric vehicle (HEV) combine the benefits of gasoline engines and electric motors and can be configured to obtain different objectives, such as improved fuel economy, increased power,or additional auxiliary power for electronic devices and power tools [16]. Thus hybrid vehicle has the advantages of good performance, fast startup and fast power response and much better fuel economy compared with fuel cell vehicle [3]. A variety of HEV exist, and the degree to which they function as EV varies as well. Fuel cell hybrid electric vehicle (FCHEV) is a non-commercial hybrid electric vehicle (HEV). The FCHEV consists of two power sources. One is fuel cell system, which is the primary power source, supplying power for constant speed driving. Another power source is the battery based peaking power source (PPS), supplying peak power to meet high power demand [11]. The FCHEV is composed of the fuel cell system, the secondary battery, the DC/DC converter, and the traction inverter/motor. The basis of the vehicle’s drive power is the output from the fuel cell, but when the fuel cell’s output power is insufficient, as it is in acceleration transitions and high load operation, a power assist is provided by the secondary battery [13]. In low

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load operation the fuel cell and the auxiliary equipment operations and stopped and the vehicle runs as a PEV on the power from the secondary battery alone. i. Low Power Mode: The fuel cell is stopped and the vehicle runs on the power from the secondary battery alone.

Fuel Cell

Battery

Converter

Fuel Cell Inverter

Battery

Motor

Converter

W h e e l

Inverter

Motor

Fig.4 Power flow during Medium power mode

iii. W h e e l

W h e e l

High Power and Acceleration Mode: Both the secondary battery and the fuel cell are in function. The secondary battery assists in the supply power if there is no sufficient energy supply from only the fuel cell.

W h e e l

Fuel Cell

Fig.3 Power flow during Low power mode

ii.

Medium Power Mode: This is driving the vehicle only using the power of the fuel cell.

Battery

Converter

Inverter

Motor

W h e e l

Fig.5 Power flow during High power mode

W h e e l

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iv.

Regenerative Breaking Mode: The output of energy from the fuel cell is stopped and regenerative energy is recovered into the secondary battery.

Fuel Cell

Battery

Converter

Inverter

Motor

W h e e l

W h e e l

Fig.6 Power flow during Regenerative braking

D. Plug in Hybrid Electric Vehicle A plug-in hybrid electric vehicle (PHEV or PHV), also known as a plug-in hybrid, is a hybrid vehicle with rechargeable batteries that can be restored to full charge by connecting a plug to an external electric power source (usually simply a normal electric wall socket). A PHEV shares the characteristics of both a conventional hybrid electric vehicle, having an electric motor and an internal combustion engine; and of an all-electric vehicle, also having a plug to connect to the electrical grid. Plug-in hybrid electric vehicle (HEV) is hybrid car with an added high capacity battery. As the term suggests, plug-in hybrid - which look and

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perform much like "regular" car - can be plugged in to a 120-volt outlet (for instance each night at home, or during the workday at a parking garage) and charged. Plug-ins run on the stored energy for much of a typical day's driving - depending on the size of the battery up to 60 miles per charge, far beyond the commute of an average American - and when the charge is used up, automatically keep running on the fuel in the fuel tank [10]. A person who drives every day a distance shorter than the car's electric range would never have to dip into the fuel tank. PHEV can store enough electricity from the power grid to significantly reduce their petroleum consumption under typical driving conditions [12]. There are two basic PHEV configurations [9]: Series PHEV or Extended Range Electric Vehicle (EREV): Only the electric motor turns the wheels; the gasoline engine is only used to generate electricity. Series PHEV can run solely on electricity until the battery needs to be recharged. The gasoline engine will then generate the electricity needed to power the electric motor. For shorter trips, these vehicles might use no gasoline at all. Parallel or Blended PHEV: Both the engine and electric motor are mechanically connected to the wheels, and both propel the vehicle under most driving conditions. Electric-only operation usually occurs only at low speeds. 1) Benefits and Challenges Less Petroleum Use. PHEV are expected to use about 40 to 60 percent less petroleum than conventional vehicles. Less Greenhouse Gas (GHG) Emissions. PHEV emits less GHG than conventional vehicles. Higher Vehicle Costs, Lower Fuel Costs. PHEV will likely cost $1,000 to $7,000 more than comparable non-plug-in hybrids. Fuel will cost less since electricity is much cheaper than gasoline. Re-charging Takes Time. Re-charging the battery typically takes several hours, but a "quick charge" to 80% capacity may take as little as 30 minutes.

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2) Performance The plug-in hybrid drive system is compatible with all vehicle models and does not entail any sacrifice of vehicle performance or driver amenities. A mid size plug-in can accelerate from 0 to 60 miles per hour at less than 9 seconds, sustain a top speed of 97 mph and maintain 120 mph for about two minutes even with a low battery. PHEV estimated retail price is higher than that of corresponding conventional vehicles but the cost for electricity to power plug-in hybrids for allelectric operation has been estimated at less than one quarter of the cost of gasoline. Compared to conventional vehicles, PHEV can reduce air pollution, dependence on petroleum and fossil fuels, and greenhouse gas emissions that contribute to global warming unless the PHEV is charged by plugging into an electric utility where coal is the predominant fuel used to generate electricity. PHEV also eliminate the problem of "range anxiety" associated to all-electric vehicles, because the combustion engine works as a backup when the batteries are depleted. Plug-in hybrids use no fossil fuel during their all-electric range and produce lower greenhouse gas emissions if their batteries are charged from renewable electricity. Other benefits include improved national energy security, fewer fill-ups at the filling station, the convenience of home recharging, opportunities to provide emergency backup power in the home, and vehicleto-grid (V2G) applications.

Fig. 7 Photo of Toyota Prius Plug-in Hybrid Vehicle [9]

E. Organic Fuel Vehicle Hydrogen fuel cells show promise for providing portable electric power generation for electric vehicles, if certain inherent problems can be overcome. While ethanol has been proposed as a hydrogen source for such a fuel cell, it too has problems that make it impractical for use in vehicles. Other organic hydrogen sources are being investigated for use in fuel cells [15]. The pure hydrogen-oxygen fuel cell has problems with storing hydrogen gas (H2). Storing a large enough volume for practical use requires storing a highly flammable gas at high pressures, adding weight and safety problems [8]. Using ethanol as a storage medium for hydrogen requires reforming hydrogen using catalysts, steam and high temperatures. This causes safety problems for automobiles as well. The different types of Organic fuel cell are: Microbe-Organic Fuel Cell: In MicrobeOrganic Fuel Cell bacterial culture is used to oxidize organic molecules to produce CO2 and H2. The temperatures required for the reaction are mild, ranging between 30 ᵒC and 60 ᵒC. These temperatures are well within the range associated with automobile engines. These systems are not very efficient, however, because the bacteria use a portion of the available energy for cell growth and replication. Power output varies over time due to changes in sugar and cell concentration. These limitations make this process more suited to electrical cogeneration production at wastewater treatment plants than portable electrical generation. Microbe-Cellulose Fuel Cell: It is the same thing as the Microbe-Organic Fuel Cell; it deserves special mention due to the specific use of cellulose as the hydrogen source instead of sugar. Cellulose is the component of biomass that is the most difficult to use for energy production except for by directly burning the material. Due to the complex requirements to maintain the bacterial cultures, such a system is more suited to the centralized production of hydrogen or electricity than for use in portable devices.

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REFERENCES Enzyme-Starch Fuel Cell: It uses a starch-water solution and a collection of thirteen enzymes to produce hydrogen. The reaction conditions are mild with the operating temperature at about 30oC. The system is relatively easy to maintain as long a nearly pure source of starch or sugar solution is feed into the cell. The enzymes drive the reaction to completion without requiring the application of outside energy. The starch is first reduced to its component sugars and then a complex series of enzyme mediated reactions results in near complete conversion to H2 and CO2 (12 moles of H2 and 6 moles of CO2 per mole of sugar). The excess hydrogen and oxygen comes from the water in which the starch is dissolved. The enzyme driven fuel cell seems to have the most potential for providing fuel cell technology for portable electronic devices and would be suitable for powering electric vehicles. The development of the Enzyme-Cellulose Fuel Cell may provide the solution to the problem of portable electrical generation for vehicles.

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CONCLUSION

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Rapidly increasing population in the cities has created a new problem of public transportation. Although in market there are various means of transportation, the general trend is to use petrol or diesel fueled assisted IC engine driven vehicles. Excess numbers of these vehicles are not economical, creating new problems related to the environmental pollution. Also the global crude-oil stock is rapidly vanishing. So it’s the time to introduce eco-friendly vehicles i.e. Alternate Energy Vehicle (AEV) to existing fuel powered vehicle in an economical and efficient way. Now-adays a few numbers of AEV are available in market. However customers are not satisfied with their operating performance. Main problems are poor battery performance, under developed control circuit and inadequate capacity of electric motor to match with the customer requirement. It is necessary to modify these AEV for public transport in city areas by increasing the degree of hybridization, leads to higher overall vehicle efficiency, fuel and energy economy.

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