A VFD (Variable Frequency Drive) converts DC to AC using a component called an inverter. Inside the VFD, the incoming AC power from the mains supply first passes through a rectifier, which converts it into DC (direct current). Then, the inverter section takes this DC power and changes it back into AC (alternating current), but with a variable frequency and voltage. This is what allows the VFD to control the speed of an AC motor precisely.
The inverter uses high-speed electronic switches, typically IGBTs (Insulated Gate Bipolar Transistors), to perform this conversion. These switches turn the DC on and off thousands of times per second in a carefully timed sequence. By controlling the switching pattern, the VFD produces a pulse-width modulated (PWM) AC output that mimics a smooth sine wave — just like the power from the grid, but at any desired frequency (for example, 30 Hz, 50 Hz, or 80 Hz).
This PWM method is the key to speed control. When the VFD outputs a lower frequency, the motor runs slower; when it increases the frequency, the motor speeds up. The inverter also adjusts voltage in proportion to frequency to maintain the correct torque and prevent overheating.
In short, a VFD converts DC to AC by rapidly switching power through IGBTs to generate a variable-frequency AC output. This combination of rectifier and inverter technology gives full control over motor speed, direction, and performance — making VFDs essential for efficient industrial automation and energy management.