Answer Posted / mr. vinayak manohar hawal

AC drives control the speed of either an induction
motor or a synchronous motor by adjusting the frequency of
the power supplied to the motor.
AC drives are also known as adjustable speed drives
(ASD) or adjustable frequency drives (AFD) or variable
frequency drives (VFD) or variable speed drives (VSD) or
frequency converters (FC).
So I think that VFD is basicaly a method of AC drive
used for changing the speed of motor.

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