Environmental Engineering Reference
In-Depth Information
6.5.2 Design of the H
∞
Current Controller
−
2550
0
2550
According to (Hornik and Zhong 2010b, 2011), the filter
W
i
was chosen as
W
i
=
1
and the weighting parameters were chosen as
ξ
i
=
100 and
μ
i
=
1
.
8. The
H
∞
controller
C
i
which nearly minimises the
H
∞
norm of the transfer matrix from ˜
w
i
to
z
i
was obtained by
using the MATLAB
R
function
hinfsyn
as
177980833
.
6502(
s
+
300)
C
i
(
s
)
=
2550)
.
(
s
+
4
.
334
×
10
8
)(
s
+
10
8
in the denominator can be approximated with the constant 4
The factor
s
+
4
.
334
×
.
334
×
10
8
without causing any noticeable performance change. The resulting reduced controller is
.
+
0
4107(
s
300)
=
.
C
i
(
s
)
s
+
2550
6.6 Experimental Results
The above-designed controller was implemented to evaluate its performance in both stand-
alone and grid-connected modes with different loads. The seamless transfer of the operation
mode was also carried out. The
H
∞
repetitive current controller was replaced with a PR
current controller for comparison in the grid-connected mode. In the stand-alone mode, since
the grid current reference was set to zero and the circuit breaker was turned off (which means
the current controller was not functioning), the experimental results with both the repetitive
current controller and the PR current controller are similar and hence no comparative results
are provided for the stand-alone mode. The PR controller was designed according to (Timbus
et al.
2009) with the plant used in Section 6.4.1 as
20
s
C
i
−
PR
(
s
)
=
0
.
735
+
2
.
s
2
+
10000
π
6.6.1 Steady-state Performance in the Stand-alone Mode
The voltage reference was set to the grid voltage (so the inverter was synchronised and ready
to be connected to the utility grid). The evaluation of the controller was made for a resistive
load (
R
A
=
R
B
=
R
C
=
12
), a non-linear load (a three-phase uncontrolled rectifier loaded
with an LC filter
L
=
150
μ
H,
C
=
1000
μ
F and a resistor
R
=
20
), and an unbalanced
load (
R
A
=
R
C
=
12
and
R
B
=∞
).
6.6.1.1 With a Resistive Load
The local load voltage
u
A
, voltage reference
u
ref
and filter inductor current
i
A
are shown in
Figure 6.8(a). Figure 6.8(b) shows the spectra of the inverter local load voltage and the local
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