Blog of motion control, electrical machinery, automation, process control, motor control, green energy...

The AC induction motor drive is the fastest growing segment of the motor control market in the world. There are various reasons for this fast growth of AC induction motor drive. These reasons are presented blow for your reference:

1. Ease of programming
2. Low investment cost for the development
3. Flexibility to add additional features with minimal increase in hardware cost
4. Faster time to market

The first type of AC motors is the synchronous motor, which rotates exactly at the supply frequency or a submultiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet.

The second type is the induction motor. The induction motor runs slightly slower than the supply frequency. The magnetic field on the rotor of the induction motor is created by an induced current.

The advantage of Direct Torque Control (DTC) of Frequency Converters (VVVF drives) is the fastest response time, elimination of feedback devices, reduced mechanical failure, performance nearly the same as the direct current (DC) machine without feedback, etc, compare to vector control and scalar control (v/f control). 

The disadvantage of Direct Torque Control (DTC) is due to the inherent hysteresis of the comparator, higher torque and flux ripple exist. Since switching is not done at a very high frequency, the low-order harmonics increases.