Environmental Engineering Reference
In-Depth Information
E
*
-
K
RMS
e
+
E
i
1
P
i
n
i
s
v
o
v
ri
+
1
i
m
i
s
Q
i
ω
i
t+
δ
i
*
ω
Figure 19.13
Robust droop controller for C-inverters
as long as
K
e
is the same for all inverters. This guarantees accurate sharing of reactive power in
proportion to their ratings. As long as the system is stable, which leads to the same frequency,
the real power can be guaranteed as well (Zhong 2012c).
According to (19.17), the output voltage is
n
i
K
e
Q
i
=
n
i
Q
i
K
e
E
∗
E
∗
+
E
∗
+
E
∗
,
V
o
=
which can be maintained within the desired range via choosing a big
K
e
. Hence, the control
strategy has very good capability of voltage regulation as well, in addition to accurate power
sharing.
The droop coefficients
n
i
and
m
i
can be determined as usual by the desired voltage drop
ratio
n
i
Q
i
K
e
E
∗
and the frequency boost ratio
m
i
P
i
ω
∗
, respectively, at the rated reactive power
Q
∗
and real power
P
∗
.
19.7.2 Simulation Results
A system that consists of two single-phase inverters powered by two separate 42 VDC voltage
supplies was used to carry out simulations to verify the design. The capacity of Inverter 1 is
25 VA and the capacity of Inverter 2 is 50 VA, with the rated power factor of 0
.
9. It is expected
that
P
2
=
2
P
1
and
Q
2
=
.
2
Q
1
. The switching frequency is 7
5 kHz and the frequency of the
system is 50 Hz. The rated voltage is 12 V and
K
e
=
=
.
20. The filter inductor is
L
2
35 mH
with a parasitic resistance of 0
.
1
and the filter capacitance
C
is 22
μ
F.
n
i
Q
i
K
e
E
∗
is 10% and frequency boost ratio
m
i
P
i
ω
∗
Assume that the desired voltage drop ratio
is 1%, respectively, at the rated real power
P
i
9
S
i
and reactive power
Q
i
436
S
i
.As
=
0
.
=
0
.
a result,
n
1
=
2
.
2 and
n
2
=
1
.
1;
m
1
=
0
.
14 and
m
2
=
0
.
07.
The capacitor is chosen as
C
o
=
479
μ
F
and the corresponding impedance at the funda-
ω
∗
)
mental frequency is
Z
o
(
j
=−
j
6
.
65
, which is capacitive and is able to dominate the
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