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
P +
c
−
P
1
sT S
+ 1
( sT )
−sτ
0
K
PP IP
+ 1 Kce
+
sT
sτ
+ 1
IP
Σp
U Ldist
−
K
sT
RL
RL
+1
3
U L
= const.
2
Fig. 3. 21. Block diagram for a simplified active power control loop in the synchronous rotating
reference frame
The model of Fig. 3. 21 can be modified as shown in Fig. 3. 22, where sum of the
small time constants is defined by:
τ = T + T
(3. 55)
Σp
S
PWM
P c
+
−
P
( sT + )
K
PP IP
1
sT
IP
−sτ
0
Kce
sτ
+ 1
Σp
U Ldist
+
−
K
sT
RL
RL
+1
3
2
U L
Fig. 3. 22. Modified block diagram of Fig. 3. 21
Please note that, τ
Σp
is a sum of small time constants, T
RL
is a large time constant
of the input choke. The similar simplifications as in Subsection 3.3.1.1 are taken into
account. From several methods of design, symmetry optimum - SO is chosen because
its good response to a disturbance
loop transfer function can be derived:
U step. For U L
= const.
the following open
Ldist
G
OP
() s
K
=
sT
IP
RLK
PP
( 1+
sTIP
) 3
U
L
( s + 1)( sT + 1) 2
τ Σ p
RL
(3. 56)
With simplification ( sTRL
) ≈ sTRL
function for power control loop:
+1 [63] gives following closed loop transfer
58