the good of AC motors

WikiAnswers - What are the advantage of AC motors and drives over ...

There are several.

1) While there are more AC motor implementations that DC motors, the more common AC motors use 3 phase power. Whether the AC is pure sinusoid or stepped DC to look like 3 phase sine wave power, the generated torque is much smoother, which has advantages over DC torque, which is not as smooth, as the commutation has inherent detents because of the constant switching due to the brushes motions from the commutation with the armature. (Assuming a brushed DC motor)

2) They are lighter in weight, smaller, and because of brushless commutation they don't require periodic replacement of the sprung carbon brushes and copper wear on the rotor, which are desirable features when using them for EVs. In today's cars, the heater/air conditioning 12VDC motors do fail because of the rotor wear and brushes.

3) They can be more efficient from a power perspective.

4) Because of the three phases they can provide better torque as well per degree of rotation.

5) The drive electronics are more complex when using a DC power sources as in EVs, however. AC drives require the synthesis of AC from DC which is inherently more complex than the pulse width and frequency methods employed with DC motor drives.

6) Most home grown EVs use DC motors because of this. All components for DC driven EVs are available off the shelf, including the motor controllers and motors.

7) I was confronted with these issues when constructing a home built EV years ago, but chose a 28HP 120VDC series wound motor (Advanced DC) because of the electronics issues.

And there are disadvantages too. That is why the DC motors still exist (and recently in our factory a few drives we are changing into DC drive - not all, a few and vice versa too)