Motor for electric vehicles

The motors used in electric vehicles should be powerful enough to satisfy the traction requirements to meet the vehicle performance and the other requirements.
1. Small and lightweight for the vehicle layout. 2. High efficiency to convert energy from electricity to traction and save fuel or electricity. 3. Durable and easy to maintain. Must be able to be used under various conditions in vehicles, such as vibration, variable temperatures and humidity. 4. Low noise. 5.Low cost. This last point is to encourage the widespread use.
Figure 5.1 shows the requirements of vehicle traction.
DC motors were used in early electric vehicles for 2 reasons: their torque and power characteristics, which meet these requirements. Speed can easily be controlled when these motors are used. But in the 90s AC motors became dominant as progress in self-switching devices was made, such as IGBT(insulated gate bipolar transistor) which enables high-power inverters to be put to industrial use.
The device in DC motors that controls the speed does not have an inverter, but the brush and commutator require periodic maintenance. And it is difficult to downsize by mechanically. DC motors will be used in a few vehicles, like electric golf carts. AC motors will be the main support of progress in electric vehicles from now on.

Categories of motors

There are various categories and names for motors. Figure 5.9 shows one of them for electric vehicles. In this figure, AC motors are categorized according to the electric current wave shape into 2 classes, sinusoidal and 'others'. As this reference figure is only for AC motors, the category of DC motors has been added.
Currently, the focus of development of motors for electric vehicles is moving from DC motors to AC motors. The most popular AC motors are the squirrel-cage type induction motor and the PM motor, which uses a permanent magnet in its rotor.
In Fig. 5.9, a brushless DC motors is categorized as non-signusoidal. This motor consists of a permanent magnet in the rotor and a wound stator, the same as a PM motor. This type is called DC brushless to exchange the actuating elements of brush and ommutatorc of DC motor by switching devices such as transistors. It came from the servomotor.
Usually, the PM motor is driven by sinusoidal current according to the rotor location, and the DC brushless motor driven by a trapezoidal or rectangular current. The wave shape of the driving current in these two motors differs from that of the inverters. But they have the same structure. In this handbook, we call them PM motors.