Environmental Engineering Reference
In-Depth Information
in the abc frame. With comparison to the case without a local load, the THD of the current i a
increased in both cases because the current reference was reduced from3Ato2A.
15.3.1.3 With an Unbalanced Load
In this experiment, an unbalanced resistive local load ( R A =
)
was connected to the system. The grid output current reference I d was set at 2 A (after
connecting the inverter to the grid) and the reactive power was set at 0 Var ( I q
12
, R B =∞
and R C =
12
0). The
output current i a , reference current i ref and the corresponding current tracking error e i in the
steady state are shown in Figure 15.5(a) and the spectra of the grid output current i a are shown
in Figure 15.5(b). The tracking performance of the PI controller implemented in both frames
worsened with an unbalanced local load because there is no mechanism in the control scheme
to deal with imbalance.
=
15.3.1.4 With a Non-linear Load
In this experiment, a three-phase uncontrolled rectifier loaded with an LC filter L
=
150
μ
H ,
C
was connected to the system. The grid current output
i a , reference current i ref and the current tracking error e i are shown in Figure 15.6(a) and the
spectra of the grid current i a are shown in Figure 15.6 (b). The tracking performance in both
frames is quite similar. The THD in both cases is considerably higher than that in the case
with resistive loads although the THD in the dq frame is slightly better than that in the abc
frame. This is because there is no mechanism in the control scheme to deal with harmonics.
=
1000
μ
F and a resistor R
=
20
5
5
i ref
i a
i ref
i a
2.5
2.5
0
0
−2.5
−2.5
−5
−5
1.5
1.5
e i
e i
1
1
0.5
0.5
0
0
−0.5
−0.5
−1
−1
−1.5
−1.5
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Time [s]
Time [s]
(a) Grid output current
, its reference
and current tracking error
5
5
THD of i a =5.54%
THD of i a =5.03%
4
4
3
3
2
2
1
1
0
0
0
5
10
15
20
25
30
0
5
10
15
20
25
30
Harmonics order
Harmonics order
(b) Spectra of the grid output current
Figure 15.5 Experimental results for a PI controller with an unbalanced resistive local load imple-
mented in the dq frame (left column) and its equivalent in the abc frame (right column)
 
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