A VFD is made up of the following except for ___.

• A. Converter
• B. Inverter
• C. Resistive Element
• D. Frequency Modulator

Answer: (C)

The key idea is what makes up a variable frequency drive and how it actually changes motor speed. A VFD converts incoming AC to DC with a rectifier (the converter), stores and smooths that energy on a DC link, and then turns that DC back into AC with an inverter that can output variable frequency and voltage. The inverter uses switching devices and a PWM scheme controlled by the VFD’s logic to set the output frequency that the motor receives. A resistive element isn’t part of these essential blocks; it would simply waste energy and doesn’t contribute to controlling speed. Sometimes a braking resistor is used in braking circuits outside the main VFD path, but it’s not a core component that defines a VFD. Also, there isn’t a separate “frequency modulator” block—the inverter’s PWM control handles changing the output frequency.