What is needed for speed control of AC motors?

What is needed for speed control of AC motors?

• A. A simple resistor network
• B. Frequency converters and variable frequency drives
• C. Solar panels
• D. Gearbox adjustments

Answer: (B)

Controlling speed of an AC motor comes from changing the supply frequency (and the accompanying voltage) delivered to the motor. For an induction motor, the speed is tied to the synchronous speed, which depends on the line frequency; you can slow or accelerate the motor by lowering or raising that frequency. A frequency converter or variable frequency drive does this smoothly, adjusting both frequency and voltage as needed to keep motor flux stable and provide controlled acceleration, deceleration, and protection. Other options won’t give reliable or efficient speed control: a simple resistor network wastes energy and distorts torque, solar panels aren’t a practical source for controlled drive power, and adjusting a gearbox only changes the mechanical output after the motor, not the motor’s electrical speed.

Controlling speed of an AC motor comes from changing the supply frequency (and the accompanying voltage) delivered to the motor. For an induction motor, the speed is tied to the synchronous speed, which depends on the line frequency; you can slow or accelerate the motor by lowering or raising that frequency. A frequency converter or variable frequency drive does this smoothly, adjusting both frequency and voltage as needed to keep motor flux stable and provide controlled acceleration, deceleration, and protection. Other options won’t give reliable or efficient speed control: a simple resistor network wastes energy and distorts torque, solar panels aren’t a practical source for controlled drive power, and adjusting a gearbox only changes the mechanical output after the motor, not the motor’s electrical speed.