How do you adjust the speed of an electric motor?
“AC motors are constant speed devices but their speed can vary if you change the input voltage or frequency or the windings that make the motor rotate. The most common and efficient way of changing the speed is to vary the frequency by using an inverter as the power supply. This method has become popular with the development and decrease in cost of power electronics. Methods involving reducing the voltage to the motor windings with resistors, transformers or motor winding taps are still in use and are the low cost and preferred methods for certain clearly defined applications.”