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Introduction

Our planet Earth is facing global warming, climate changes and Greenhouse effect due to air pollution. Vehicles fuelled by gasoline or diesel release carbon monoxide (CO), carbon dioxide, nitrogen oxides, volatile organic compounds (VOCs), particulate matter and sulphur dioxide.

Carbon monoxide inhibits the ability of the blood to carry oxygen and can also cause permanent damage to the nervous system. Nitrogen oxides affect lungs and increase the susceptibility of young children and the elderly to respiratory infections. Nitrogen oxides also contribute to the formation of acid rain whose acidity kills plants and fish. Benzene, a known carcinogen, is an example of a toxic VOC found in vehicle exhaust. Particulate matter (PM) causes lung problems leading to shortage of breath and damage to lung tissue. At concentrations above 5 micrograms per cubic metre particulate matter present a significant cancer risk. Many PMs are recognised as toxicants and carcinogens, as well as hazards to the reproductive and endocrine systems.

Electric car Motors

So we need to encourage cleaner, more efficient energy usage to address air pollution. Electric vehicles release less pollutants than gasoline and diesel-powered cars. Hence they are eco-friendly alternative to gasoline-powered vehicles.

An electric car is powered by an electric motor rather than by a gasoline engine. The gasoline engine is replaced by an electric motor which draw power from rechargeable batteries through a controller. The controller takes DC power from the batteries, converts it to AC three phase power and delivers it to the motor. The signal from accelerator, through a potentiometer connected to the controller, decides the amount of power to be delivered to the electric car's motor. There are two potentiometers the controller reads and it checks whether their signals are equal or not; it is a safety measure in case of a potentiometer failure. The controller additionally provides a charging system for the batteries, and a DC-to-DC converter to recharge the 12 V accessory battery.

Range anxiety is an important issue pertaining to reliability of electric vehicles (EVs), it is the uncertainty regarding the vehicle's state of charge (SoC) and it's adequacy in reaching the destination. So, battery is a very critical component of electric car.

Electric car batteries

Battery is the only energy store, and the component with the highest cost, weight and volume. In hybrid vehicles too, battery is a key component. A battery is two or more electric cells joined together. The cells convert chemical energy to electrical energy. The cells consist of positive and negative electrodes joined by an electrolyte. It is the chemical reaction between the electrodes and the electrolyte which generates DC electricity. In case of secondary or rechargeable batteries, the chemical reaction can be reversed by reversing the current and the battery returns to its initial charged state.

Battery problems

The 'lead acid' battery is the most well known rechargeable type, but there are others which include nickel iron, nickel cadmium, nickel metal hydride, lithium polymer and lithium iron, sodium sulphur and sodium metal chloride. NiMH batteries increase the range of the car and the life of batteries but they are more expensive than lead acid ones. Lithium ion is currently used where emphasis is on high performance rather than on cost. The prices are expected to fall soon and electric cars would be available at broader price Range. Fuel cells could be an alternative as they are much smaller and instantly rechargeable. Fuel cells powered by pure hydrogen exhibit none of the environmental hazards associated with gasoline. There is a lot of research and development going on in this field and it may take some time before we can get reliable and affordable fuel cells to power cars. Electric cars also have a normal 12 V lead acid battery to power up the accessories like headlights, radios, fans, computers, airbags, wipers, power windows inside the car. A DC-to-DC converter is required to charge this battery.

Battery has a range of performance criteria including specific energy, energy density, specific power, typical voltages, amp hour efficiency, energy efficiency, commercial availability, cost, operating temperatures, self-discharge rates, number of life-cycles and recharge rates. Energy availability also varies according to ambient temperature, charge and discharge rates, battery geometry, optimum temperature, charging methods and cooling needs. Limited life, self-discharge, reduced efficiency at higher currents, recycling of batteries are concerns.

Charging an Electric Car

Robust charging system is needed to recharge the batteries in an electric car. The charging system pumps electricity into the batteries and monitor the battery voltage, current flow and battery temperature to minimize charging time and to avoid damage during the charging process. An important feature of the charging process is "equalization". An electric vehicle has a string of batteries, which are very similar but not identical. They have slight differences in capacity and internal resistance. Equalization of charging solves the problem of unequal charging in batteries to avoid weak links in the string of batteries. Some batteries are slightly overcharged to make sure that the weakest cells are brought up to their full charge capacity, thereby achieving equalization of batteries without damaging the strongest batteries due to overcharging. There are more sophisticated solutions to scan the batteries, to measure individual voltages, and to send extra charging current through the weakest module. In Plug-in chargers, alternating current is rectified to direct current and this is used to charge a large capacitor. Power electronics are used to switch the current to the capacitor on and off, thus maintaining the DC voltage within narrow bands.

Specifications of Electric car

Computer based simulation allows us to quickly experiment with various aspects of the vehicle, such as motor power, battery type and battery size to see how the changes affect the performance and range of the vehicle. In order to maximise the fuel efficiency, the vehicle's mass, aerodynamic drag and rolling resistance have to be minimised, where as motor efficiency and transmission efficiency have to be maximised. Main specifications of the car people look at are range, speed, acceleration, type of use, performance up hill, legal requirements, target cost, life, maintenance requirements, environment, aesthetics and comfort.

Energy to electric cars

Alternative sustainable forms of energy such as solar, wind, hydro, tidal, wave, biomass can be used to provide energy to electric vehicles via the grid. Sustainable forms of energy can be used to provide electricity for rechargeable battery cars and also to provide and process fuel for metal air batteries and fuel cells. Using alternative forms of power to energise electric vehicles would make a real impact on the environment, totally eliminating hazardous emissions resulting from the ever expanding auto-mobile industry.