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Vector Control of the Induction Motor 1.pdf


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Vector Control of the Induction Motor
Summary
Unlike a DC motor, an AC induction motor is much more complicated to control in a
fast way. The stator current (field winding) and the rotor current (armature winding) can
be changed independently from each other in a DC motor. This is not possible in an
induction motor, where stator and rotor current are dependent on the same
(stator)voltage (𝒖𝑠𝑠 in figure 1). An increase of this voltage will only have a relatively
slow response on the magnetising current because of the large Lm.
Vector control makes it possible to split up the stator current in a part that is responsible
for the magnetising of the air gap and a part that handles the torque demand. The former
is held a constant (because of the slow response), while the latter is used to control the
torque or the speed. In this way torque and speed in an AC motor can be changed as
quickly and efficient as a DC motor.

𝒊𝑠𝑠
+
𝒖𝑠𝑠

Rs

Lrl

Lsl

𝒊𝑟𝑠

𝑠
𝒊𝑚

Lm

Figure 1 Dynamic equivalent scheme

Rr’

+ s
jwyr