Electric vehicles (EV) are receiving a great interest as an alternative to conventional transportation on oil with the purpose to decrease noise, environmental pollution by reducing carbon emissions and to reduce dependence on oil (Lowry & Larminie, 2012). Moreover, using nuclear and alternative energy including renewable allows to produce zero release of carbon dioxide by vehicles. Currently, road vehicles just reached the stage when electric cars are produced in quantity but still not widely used. First, electric cars have significantly less range. Second, it takes much more time to recharge batteries (several hours for lead acid battery) than to put petrol into a vehicle (approximately one minute). Second, batteries are much more expensive than internal combustion (IC) engine. On the other hand, electric trains are popular and more preferred as they do not require much maintenance.
Early attempts to build electric transportation began already in nineteenth century. In 1821 Michael Faraday developed an electric motor and in 1832 British scientist Sturgeon designed first commutator-type direct current (DC) motor that was able to turn machines. First electric locomotive was invented by Robert Davidson in 1837 based on non-rechargeable batteries and in 1895 the locomotive was firstly used on a main line of Baltimore Belt Line, USA, for a range of 4 miles. In 1880 first electric trolleys and trams were experimentally used in St Petersburg, Russia. Recent novelty in building electric vehicles is development of the lithium batteries that have more reasonable power and charge time. One of the most famous examples using this technology is Tesla sport cars. Technology that provides longer range is fuel cells which usually run on hydrogen. For example, Honda’s FCX Clarity runs on hydrogen.
Battery EVs:
EV comprises electric battery, an electric motor and a controller. The battery for energy storage can be recharged using charger via a plug. Controller is used to control the supplied power and thus, motor speed and direction (forward and reverse) which is called ‘two-quadrant controller’. Moreover, there is a mechanism called regenerative braking that allows to simultaneously slow down the vehicle and regain energy and is called ‘four-quadrant controller’. Nissan produces commercial EVs.
Traditional type of batteries that is rechargeable is lead acid battery (Lowry & Larminie, 2012). Negative plates of lead acid cells have an active material as a spongy lead and positive plate have lead dioxide. These plates are plunged into dilute sulfuric acid as an electrolyte. As a result of the reaction, lead sulfate and water are produced and energy is released. The most important feature of lead acid battery is that voltage fall can be considered the smallest among other vehicle batteries due to its remarkably low value of internal resistance. However, there is also an issue of self-discharging which occurs because of lead and lead dioxide instability in sulfuric acid. The result of this process is loss of water and its conversion to hydrogen and oxygen and this leads to the decrease in battery lifespan. Overall life of lead acid battery is about 700, however, experience suggests that 1200-1500 cycles are possible which are 7-8 years.
Other battery types include nickel iron, nickel cadmium, nickel metal hydride, lithium polymer and lithium iron, sodium sulfur, and sodium metal chloride and among recent ones are aluminum-air and zinc-air. One of the most promising technologies is “Zebra” battery based on sodium-nickel chloride which have operating temperature range up to 360 degrees and can be also utilized in cold conditions (Perdontis, 2011).
The IC Engine/Electric Hybrid Vehicle
There are several architectures for hybrid vehicles. The most commonly used it combination of IC engines and battery, electric motor, and generator. There exist two designs: series, where vehicle is operated by one or more electric motors directly supplied from generator and parallel, in which machine is driven by engine working through a transmission system or motors which can also be connected directly to the wheels. Both arrangements provide regenerative braking. Series hybrid vehicles are not very popular as power cannot be passed mechanically to the wheels but rather should go through both motors and generator. On the other hand, parallel allow smart use of battery and IC engine separately and in combination. Commonly, in these systems electrical and mechanical power outputs are connected with torque-couplers or speed-couplers (Khajepour, Fallah & Goodarzi, 2014). One of the most successful examples on the market is non-rechargeable hybrid Toyota Prius.
Fueled EVs
Working principle of fueled EVs is similar to battery EV, however, instead electric battery fuel cell or metal air battery is used. Another alternative is zinc-air batteries. Fuel cell that is device converting hydrogen and oxygen into electricity prove to be very efficient for powering EVs (Sperling, 2013). Its energy storage principle is different from conventional battery and it generates electricity continuously as the fuel is supplied, therefore it solves the problem of limited range. Moreover, it is twice as efficient in terms of energy supply as gasoline engine and does not produce pollution, noise, or heat. Significant issue of fuel cells is that they are based on hydrogen fuel the onboard storage of which is not easy. To resolve the issue, hydrogen can be made from a fuel such as methanol, for example, Necar 5 car uses this approach
EVs which use Flywheels or Supercapacitors
Alternative source of energy that potentially can be used vehicles are flywheel and supercapacitors. However, these devices have small energy density. British inventor John Parry designed EV, tram, driven from flywheel speeded up with an electric motor and using an infinite variable cone and gearbox. The engineer also suggested to use the system with a common battery to provide it the ability to quickly take and give out energy and produce high efficiency of regeneration. Energy stored in flywheel is E=0.5Iw2 (Joules).
Supercapacitors (capacitors with large plate areas) are usually used in hybrid machines where the main source of energy is IC engine or fuel cell. In some application capacitors are used to recover kinetic energy during deceleration and to rise peak power during rapid acceleration. Energy stored in capacitor is E=12CV2 (Joules).
Solar-Powered Vehicles
There is also an active research in using solar power for vehicles. In 1996 Honda Dream solar-powered car won the World Solar Challenge achieving an average speed of 85 kilometers per hour. However, the vehicle is very expensive and its performance is good only in the presence of intensive sunshine. Nonetheless, the idea of using solar energy for powering vehicles is feasible and in future it can be an alternative to electric batteries.
Vehicles using Linear Motors
Another kind of electric motor used with magnetic levitation and gaining an increasing interest is linear motor. Stator and rotor of a linear motor are unrolled and produce linear motion rather than rotary.
Electricity Supply
Electric trains usually are powered from supply rails. Steel shoes connected to the train supply current and are in contact with parallel to the track supply rails. Direct current is mostly used for supply rails. There are two different configuration used: three-rail when current returns through the common running rail and four-rail in which current return via additional fourth rail. Another option are overhead wires mounted on insulators.
For road transport power supply is not enough investigated and tested topic yet. One promising approach is inductive power transfer (IPT) which was firstly proposed by Nikkola Tesla and now the patent is in the ownership of Wampfler Ltd company. IPT concept implies transferring electrical energy to vehicles without any physical contact. IPT works similar to transformer and has two circuits: primary that is on the track and pickup which is secondary. But opposite to transformer IPT has significantly larger air gap and operating frequency. Power of the track produces high-frequency AC in the cable. Track conductors generate AC magnetic field which is captured by pickup and then generates electrical energy in the coil. AC power is then converted to DC by pickup regulator.
Electric Vehicle modelling
For an electric vehicle modelling its performance (top speed and acceleration) and range are considered. First, force moving the vehicle forwards called tractive force should be enough to be able to surmount the rolling resistance, aerodynamic drag, vehicle weight’s vertical components, and accelerate the vehicle. Rolling resistance force is nearly constant and is proportional to the weight of the vehicle and can be found as Frr= μrrmg, μrr is rolling resistance coefficient dependent on tyre type and tyre pressure and can be easily found when a vehicle drives with a steady and low speed. Aerodynamic force occurs as body moves through the air and can be found by Fad=12ρACdv2 with air density ρ, frontal area A, and drag coefficient Cd. Using force body diagram vertical component of vehicle weight, hill climbing force, can be calculated as Fhc=mgsinψ. Finally, the force for linear acceleration can be found using Newton’s third law Fla=ma. In addition, rotational acceleration should be considered and it is given as Fwa=IG2ηgr2a, where I is the moment of inertia of the motor’s rotor, G is gear ratio, r is tyre radius, and ηg is gear system efficiency which is never 100% in real life conditions.
Second, as tractive force is found, range should be estimated which is energy required to drive the vehicle for each interval of the driving cycle. There exist two tests to estimate the vehicle range. First is simulation at the constant velocity and second is simulation and drive in reality with changing speeds. It is assumed that if time interval is chosen to be 1 second, consumed energy and power are equal. Power is found as tractive force times the velocity Pte=Fte×v and then energy necessary to move the car for one interval is found. Considering motor, controller, and gearbox inefficiencies it is obvious that motor’s power is not equal to the traction force and more electrical power need to be supplied to the motor than the mechanical output: Pmot_in=Pmot_outηm and Pmot_out=Pteηg when vehicle is being driven and Pmot_in=Pmot_out×ηm and Pmot_in=Pte×ηg when vehicle is decelerating. Finally, battery power is found as Pbat=Pmot_in+Pac.
Conclusion
Electricity and magnetism are making a significant influence on the future transportation. Currently we observe the development of traditional light-weight vehicles such as golf carts, electric bicycles, electric trains and maglev trains levitated by magnets and running without wheels. Electric road vehicles still are in minority and the introduction and rapid development of fuel cells provides opportunities to its evolution. However, despite overall current state of electric vehicles is not developed yet, it is more than likely that in future we will shift from petroleum-powered vehicles to electric ones as energy sources for EVs are more efficient in terms of power loss, offer lower operating costs, should require less maintenance and infrastructure, much less taxes, and finally, it is necessary measure towards solving global climate change issue (Sandalow & Shah, 2009). With development of new energy source including solar an alternative energy power station the future of electric vehicles is really promising.
References
Khajepour, A., Fallah, M., & Goodarzi, A. (2014). Electric and Hybrid Vehicles. Hoboken: Wiley.
Lowry, J., & Larminie, J. (2012). Electric Vehicle Technology Explained (2nd ed.). Somerset, NJ, USA: John Wiley & Sons.
Perdontis, M. (2011). Battery manufacturing and electric and hybrid vehicles. New York: Nova Science Publishers.
Sandalow, D., & Shah, S. (2009). Washington, US: Brookings Institution Press.
Sperling, D. (2013). Future Drive: Electric Vehicles and Sustainable Transportation. Washington DC, USA: Island Press.
