Answer / prashant kumar sharma

Input frequency and Voltage at the VFD is constant but at
the output at the VFD is variable.
secondly the power factor at the Driven end is changing wrt
to load.
more over the Active and reactive part of Power is
deviating wrt to above factors thus the power at the input
and output of VFD are different.

in DOL none of the parameter like Voltage or Frequency are
changed thus Power remain same.

Answer / shyam

in VFD, fist ac power rectify into dc power then convert it
into variable ac power.in this process energy loss as heat.
in DOL none of the parameter like Voltage or Frequency are
changed thus Power remain same.

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