What method do VFDs use to convert fixed-frequency AC line voltage to power motors?

Variable Frequency Drives (VFDs) are used to control the speed and torque of electric motors by adjusting the frequency and voltage of the power supplied to them. The method they primarily utilize for this conversion is Pulse Width Modulation (PWM).

PWM is a technique that involves rapidly switching the voltage on and off to create a variable output voltage. This allows VFDs to simulate a continuous AC voltage while shifting the frequency, which effectively controls the speed of the motor. The rapid switching creates a series of pulses, the width of which can be adjusted. By changing the width of these pulses, the average voltage and, consequently, the output frequency can be manipulated, providing precise control over motor performance.

Sine wave modulation is another method utilized for generating signals, yet it does not offer the same level of efficiency or flexibility in motor speed control as PWM. Frequency division relates to reducing the frequency of a signal but does not apply directly to the operation of VFDs. Phase angle control, primarily used in thyristor-based circuits, controls the power by adjusting the phase at which the voltage is applied but is less common in modern VFDs compared to PWM.

Hence, the choice of Pulse Width Modulation as the method used by VFD