Environmental Engineering Reference
In-Depth Information
Figure 6.7
Sketch of a grid-connected three-phase inverter with the cascaded current-voltage control
strategy
phases because of the stable neutral line available. The control structure for the three-phase
system is shown in Figure 6.7. A traditional
dq
phase-locked-loop was used to provide the
phase information needed to generate the three-phase grid current references via a
dq
/
abc
transformation from the current references
I
d
and
I
q
. The internal model was implemented
with the capability to adapt to the frequency change in the grid described in Chapter 5,
according to (Hornik and Zhong 2010b).
6.5.1 Design of the H
∞
Voltage Controller
According to (Hornik and Zhong 2010b, 2011), the weighting function was chosen as
W
u
=
−
2550
0
for
2550
f
=
50 Hz and the weighting parameters were chosen as
ξ
u
=
100 and
1
85. For the parameters of the plant given in Table 3.1, the
H
∞
μ
u
=
1
.
controller
C
u
which
nearly minimises the
H
∞
norm of the transfer matrix from ˜
w
u
to
z
u
was obtained by using
the MATLAB
R
function
hinfsyn
as
649(
s
2
10
8
)
748
.
+
6954
s
+
3
.
026
×
C
u
(
s
)
=
10
8
)
.
(
s
+
2550)(
s
2
+
7969
s
+
3
.
043
×
It can be reduced to
748
.
649
C
u
(
s
)
=
2550
,
s
+
without causing noticeable performance degradation, after cancelling the poles and zeros that
are close to each other.
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