Space Vector Modulated – Direct Torque Controlled (DTC – SVM ...

3. Vector Control Methods of Induction Motor
dΨ
dt
r
L
R
R
M r
r
= I
sd
− Ψ
r
(3.6)
Lr
Lr
The motor torque can by expressed by rotor flux magnitude
component I
sq
as follows:
Ψ
r
and stator current
M
e
m
L
s M
= pb
Ψ
rIsq
(3.7)
2 Lr
Equations (3.6) and (3.7) are used to construct a block diagram of the induction
motor in
d − q coordinate system, which is presented in Fig. 3.2.
R
L
r
r
I sd
LM
R
L
r
r
∫
Ψ r
M e
I sq
p
b
ms
2
L
L
M
r
M e
1
J
∫
Ω m
M L
Fig. 3.2. Block diagram of induction motor in
d − q coordinate system
The main feature of the field oriented control (FOC) method is the coordinate
transformation. The current vector is measured in stationary coordinate
α − β .
Therefore, current components
I , I
β
must be transformed to the rotating system
sα
s
d − q . Similarly, the reference stator voltage vector components U
s α c
,
U
s β c
, must be
transformed from the system
d − q to α − β . These transformations requires a rotor
flux angle γ sr
. Depending on calculations of this angle two different kind of field
oriented control methods maybe considered. Those are Direct Field Oriented Control
(DFOC) and Indirect Field Oriented Control (IFOC) methods.
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