Environmental Engineering Reference
In-Depth Information
unbalanced resistive and non-linear loads were connected to the three-phase inverter to gen-
erate nearly zero, clean and distorted currents, respectively. The transient performance was
tested when the resistive load connected to the three-phase inverter was changed.
13.4.1 Steady-state Performance
13.4.1.1 When the Neutral Current is Clean
The three-phase inverter was connected to a resistive local load in the open-loop mode to
generate
i
N
and the controllers
C
1
and
C
3
were tested when the RMS value of the neutral
current
i
N
was
I
N
=
0A,
I
N
=
1 A and
I
N
=
2 A, respectively. The results are shown
in Figure 13.7 when
I
N
=
0A(
R
A
=
R
B
=
R
C
=
), in Figure 13.8 when
I
N
=
6
1A
(
R
A
=
R
C
=
and
R
B
=
) and in Figure 13.9 when
I
N
=
2A(
R
A
=
R
C
=
6
12
6
and
R
B
=∞
), respectively. The controllers maintained a small voltage shift in all cases. The
majority of the neutral current was forced to flow through the inductor and
i
C
remained nearly
0. There was no visible fundamental component in
V
a
v
e
when
C
1
and
C
3
were used. Although
there was visible 3rd harmonics in
V
a
v
e
when
C
1
was used, no visible 3rd harmonics appeared
in
V
a
v
e
when
C
3
was used and the variation of
V
a
v
e
was very small. The neutral point shift
remained almost unchanged when the neutral current was increased.
4
4
i
R
i
S
i
T
i
R
i
S
i
T
2
2
0
0
−2
−2
−4
−4
0
0.01
0.02
0.03
0.04
0.05
0.06
0
0.01
0.02
0.03
0.04
0.05
0.06
Time [s]
Time [s]
(a) Three-phase currents
and
of the inverter to generate the neutral current
4
4
i
C
i
L
i
N
i
C
i
L
i
N
2
2
0
0
−2
−2
−4
−4
0
0.01
0.02
0.03
0.04
0.05
0.06
0
0.01
0.02
0.03
0.04
0.05
0.06
Time [s]
Time [s]
(b) Neutral current
, capacitor current
and inductor current
1
1
V
ave
V
ave
0.5
0.5
0
0
−0.5
−0.5
−1
−1
0
0.01
0.02
0.03
0.04
0.05
0.06
0
0.01
0.02
0.03
0.04
0.05
0.06
Time [s]
Time [s]
(c) Neutral point shift
Figure 13.7
Steady-state responses when a balanced resistive load was connected to the three-phase
inverter (
I
N
=
0 A): with the controller
C
1
(left column) and with the controller
C
3
(right column)
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