Flux vector control basics
ATV71
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The control of an asynchronous motor is made more difficult by the fact that the
electrical parameters (current, voltage, flux) are alternating.
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Furthermore, flux and torque are dependant upon current.
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The principal of flux vector control consists in transforming the machine
equations in such a fashion so as to::
– use variables as though the are continuous and no longer alternating,
– simplify the equations in order to decouple the flux and torque variables.
Flux r = K1 Id
Torque C = K2 s Iq
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Flux is proportional to the Id component of current.
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If the flux is constant, the torque is proportional to the Iq component of current.
Bertrand Guarinos STIE
ATV71 M3 motor control V2
Summary
1
Flux vector control basics
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ATV71
Vector control allows the controller to separate the torque producing current and
the flux producing current
This is analogous to a DC motor with separate excitation.
Flux is maintained constant and set at a point to obtain constant torque over the
entire speed range.
Asynchronous
Motor
DC Motor
r
r
s
s
Id Flux
I inductive
Torque
I induced
Iq
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The vector control has a speed estimation function that allows the full time
correction of torque and flux.
Thus the performance is much better, for low speed torque, dynamic response,
and speed precision compared to a scalar volts/Hertz law.
Bertrand Guarinos STIE
ATV71 M3 motor control V2
Summary
2
Flux vector control basics
ATV71
 Comparison of U/F and Vector control
Flux Vector Control
U/F Law
Automatic Compensation
(Rs and slip)
Manual Compensation
(U0 voltage at origin)
C/Cn
C/Cn
200 %
100%
F hz
1 3
Bertrand Guarinos STIE
FrS
F hz
5
10
ATV71 M3 motor control V2
FrS
Summary
3