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Drives / Inverters

What Is a Frequency Inverter (VFD)?

The basic blocks of the drive that controls AC motor speed by changing frequency: rectifier, DC link and inverter stage.

4 min readUpdated: 2026-07-05

A frequency inverter (VFD/AC drive) first converts fixed-frequency mains to DC, then reconstructs three phases at the desired frequency to control motor speed.

Three core blocks

Rectifier
AC → DC (diode/active front end)
DC link
Filtering + energy buffer (capacitors)
Inverter stage
DC → variable-frequency AC (IGBT/PWM)
Most drive faults concentrate in one of these three blocks: rectifier (input), DC link (capacitors) or inverter (IGBT).

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