How does a Variable Frequency Drive work

The first stage of a Variable Frequency AC Drive, or V FD, is the Converter. The converter is comprised of six diodes, which are similar to check valves used in plumbing systems. They allow current to flow in only one direction; the direction shown by the arrow in the diode symbol. For example, whenever A-phase voltage is more positive than B or C phase voltages, then that diode will open and allow current to flow. When B-phase becomes more positive than A, then the B-phase diode will open and the A-phase diode will close. The same is true for the 3 diodes on the negative side of the bus. Thus, we get six current pulses as each diode opens and closes. This is called a six-pulse V FD, which is the standard configuration for current Variable Frequency Drives.