Direct Power and Torque Control of AC/DC/AC Converter-Fed ...

3. Vector Control Methods of AC/DC/AC Converter-Fed IM Drives – A Review
U dcc
= const.
U dccc
sT pfu
1
+ 1
U
dcc+
−
( sT )
P VSR
K
PU IU
+ 1
1 +
sTIU
1+ sT IT
P load
−
P cap
1
sCU dcc
U dc
U dcf
1
sT U
+ 1
Fig. 3. 31. Block diagram for a simplified DC-link voltage control loop
The block diagram of Fig. 3. 31 can be modified as shown in Fig. 3. 32.
U dccc
sT pfu
1
+ 1
U dcc
+
−
( sT + )
K
PU IU
1
U
sT
IU
dcc
sT UT
1
+ 1
P VSR
+
P load
−
P cap
1
sCU dcc
U dc
U dcf
For simplicity it can be assumed that:
Fig. 3. 32. Modified block diagram of Fig. 3. 31
T = T + T
(3. 69)
UT
U
IT
Where,
T
U
is DC-link voltage filter time constant, T UT
is a sum of small time
constants and
CU
dcc
is an equivalent of integration time constant. So, the open loop
transfer function can be derived:
G
Uo
() s
IU
PU
( sTIU
+ 1)
( sTUT
+ 1) sCU
dcc
K
= (3. 70)
sT
This gives following closed loop transfer function:
() s
( sT + 1)
K
= (3. 71)
T CT U
PU IU
GUz
2
3
K
PU
+ sTIU
K
PU
+ s TIUCU
dcc
+ s
IU
UT
dcc
The method of symmetrical optimum [134] is used to synthesize the DC-link voltage
controller. Therefore, square of the module of Eq. (3.71) takes a form:
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