Electric cars are rechargeable vehicles powered by electric motors. Electric motors for cars convert electrical energy into mechanical energy. Controllers regulate and control power received from rechargeable batteries to run the motors. The motors could be AC or DC motors. DC motors for electric cars could be further classified as permanent magnet, brushless, and shunt, series and separately excited. The DC uses electricity and a magnetic field to produce torque, which rotates the motor. The simplest DC electric motor comprises of two magnets of opposite polarity and an electric coil forming an electromagnet. The properties of attraction and repulsion are used by the DC electric motor to convert electricity into motion -- opposing electromagnetic forces of magnets generate torque causing the DC motor to turn. Characteristics desirable of electric motors for cars include peak power, ruggedness, high torque-to-inertia, high peak torque, high speed, low noise, minimal maintenance and ease of use. Current generation electric motors are combined with inverters and controllers for a wide range of torque.
The abundance of series DC motor has allowed it to be tested on a variety of vehicles. The Series DC are robust and long-lasting, and the power density provides the best value for money. The torque curve suits a variety of traction applications. However, it is not as efficient as the AC Induction motor. The commutator brushes wear out and maintenance activities are required periodically. It is also not suitable for regenerative braking, that allow vehicles capture kinetic energy to recharge batteries.
DC motors are simpler and cost less, and have been widely used in demonstration electric vehicles. Brushless DC have no commutators, and are more powerful and efficient than commutator motors. Such DC motors, however, require more sophisticated controllers. Brushless DC in electric cars can give efficiencies up to 90%, and no servicing is required for up to hundred thousand kilometers. Experts at Floyd Associates (2012) argue that electric cars with DC Brushless motors can achieve the highest speed but slowest acceleration; AC Induction can achieve the fastest acceleration with average top speed; Permanent Magnet motors can achieve top speed and average acceleration; and Switched Reluctance motors provide the most cost-effective solution.
Tesla Motors is a pioneer in the development of electric vehicles. Tesla Roadster, for example, consumes 110 watt-hours for a kilometer-long drive. Electric vehicles based on current technology cover an average of 160 km between charges. Deloitte (2012) argues that the greatest challenge in the development of electric cars is energy density, or the amount of electrical energy that can be stored per unit mass in a battery.
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