Answer / deepak g

In I.M, we generally consider the flux proportional to
torque and the slip prop. to speed in scalar control. Now
this is actually not valid for vector control. In vector
control we need to consider a dc drive analogy. i.e. the
torque is proportional to the armature current only and does
not affect flux (armature and field current which are
perpendicular to each other forming independent phasors ).So
by torque control i think it means controlling the real
component of the stator current which is formed after
resolving the stator current into quadrature and direct axis
currents.

Answer / vishok

VVVF stands for variable voltage variable frequence. These
are simple V/F drives for the steady state applications eg
fan and pump which allows a lot of time for a speed change.

Here a speed set point serves a single command for speed
change and strength of magnetic field in motor.Therefore
Separate torque control is not possible in VVVF drives. So
the torque always remains constant in VVVF drives which
equals to V/F. The voltage and frequency in VVVF drives
varry in proportion in order to maintain the torque.

Answer / hiren morkar

Scalar control is V/f control which you can use where load
behaviour is not dynamic, in scalar control u can not goes
above rated torque.the closed loop scalar control give more
precise solution.the closed loop scalar control give more
precise solution.
Vector control controling torque by seprated magnetizing
current and torque producing current, so that it can
control torque by controling flux.(magnetizing current).
It is used where load behaviour is dynamic ,the closed loop
control give more precise solution.

Answer / ajay daultani

torque vector control is nothing but control of two vector
components of stator current i.e magnetizing current Im and
rotor ( or torque ) current Ir .

Ir = Is cos( fie )
Im = Is sin ( fie )

Answer / arun

ya the above answer is correct..v/f is directly
proportional to flux .we have to maintain the flux constant
to produce constant torque..actually vector control means
tat we have to currents Idirect axis and Iquadrature
axis..Id controls the flux of the machine.Iq controls the
torque of the machine independently.

Answer / vinod

it one kind of control method in the vfd.
for example the the unwinder and rewinder has a opposite
torque directions.
in unwinder the speed and torque will be in opposite
direction
in rewinder the speed and torque will be in same direction.
so,an effective toruqr control can be made with a vvfd.

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