Which of the following devices controls the speed of an AC motor?

The Variable Frequency Drive, or VFD, is specifically designed to control the speed of an AC motor by varying the frequency and voltage of the electrical supply. By adjusting these parameters, the VFD allows for precise motor speed control, enabling better performance, energy efficiency, and flexibility in various applications. This makes it particularly useful in scenarios where different motor speeds are required or when load conditions vary, as it can adjust the output to match the requirements of the system.

The capability of a VFD to modify notch frequencies directly impacts the rotational speed of the AC motor, since the speed of an AC motor is directly proportional to the frequency of the supply voltage. Therefore, using a VFD allows for smooth acceleration and deceleration of the motor, enhancing the overall control and usability in industrial and commercial applications.