Virtually all industrial factories and buildings are powered with AC that reverses the current direction of about 50 times per second. Particularly, within an electric drive system, it is the AC motor that converts the electrical energy kept in large batteries to mechanical energy. This electric motor is made up of a stationary part called the stator and the moving part called the rotor. The rotor consists of a series of magnets while the current carrying stator often comes in the form of an iron ring. This ring is then designed to generate a rotating magnetic field.
Conversely, in a DC motor, the power is transmitted to the inner rotor which is the opposite case in an AC motor where power is carried to the outer coils or the stator. When it comes to the use of electric motors in electric vehicle traction drive systems, there are three common types of AC motors utilized in the automotive industry. One type is the induction motors. This motor technology is mature already and has been used in many industries, particularly production vehicles. It is mainly because it provides high starting torque and great reliability. However, the overall efficiency and power density of induction motors are lower than that of internal permanent magnet or IPM motors.
The IMP motors, on the other hand, are very beneficial in making electric drive vehicles due to their high efficiency and power density. Yet, the main challenge in using this type of AC motor is the high costs of the rare earth permanent magnets used in manufacturing it. But the automotive industry is still looking forward to using this motor in the coming years. The last option is the switched reluctance motor which is easy to make and has the lower costs. However, it is less efficient than the other two motors and generates more vibration and noise. However, a switched reluctance AC motor can tolerate both high speeds and temperatures with its rugged structure.
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