Disadvantages of AC Motors
Although the most common and simple industrial motor is the three phase AC induction motor, there are still disadvantages of ac motor.
Below are the disadvantages of ac motors.
1) Expensive speed control
Speed control is expensive. The electronics required to handle an AC inverter drive are considerably more expensive than those required to handle a DC motor.
However, if performance requirements can be met -- meaning that the required speed range is over 1/3rd of base speed -- AC inverters and AC motors are usually more cost-effective than DC motors and DC drives for applications larger than about 10 horsepower, because of cost savings in the AC motor.
2) Inability to operate at low speeds
We know that standard AC motors should not be operated at speeds less than about 1/3rd of base speed. This is due to thermal considerations. In fact a DC motor should be considered for these applications.
3) Poor positioning control
Positioning control is also expensive and crude. Even a vector drive is very crude when controlling a standard AC motor. Servo motors are more appropriate for these applications.
For advantages of AC Motors (1) and advantages of AC Motors (2)
