Environmental Engineering Reference
In-Depth Information
400
2.5
i
d
=0
u
o
i
d
=0
e
2
300
1.5
200
1
100
0.5
0
0
−0.5
−100
−1
−200
−1.5
−300
−2
−400
−2.5
0
0.05
0.1
0.15
0.2
0.36
0.37
0.38
0.39
0.4
Time (sec)
Time (sec)
(a) Output voltage and tracking error (
i
d
= 0
)
(b) Steady-state tracking
error
e
Figure 4.9
Output voltage and tracking error with a purely resistive load of 50
error decayed rapidly, as shown in Figure 4.11(b), and in the steady state it was very small
(with ripples of about 7 V due to the effect of the PWM switching). Although the external grid
was extremely distorted, the microgrid was very clean with a THD of about 1
20%, mostly
due to the switching noise. In this simulation, the disturbance
i
d
was set to 0 and the load was
the nominal load.
Another simulation was done when there was a shallow sag in the grid. The sag was
.
−
10%
from 0
6 sec, as shown in Figure 4.12(a). The maximum dynamic error, as shown
in Figure 4.12(b), was less than 6 V (peak) and the microgrid reached the steady state within
5 mains cycles. In this simulation,
i
d
=
.
4 sec to 0
.
0 and the PWM block and the inverter were modelled
as a saturation.
2.5
80
2
60
1.5
40
1
20
0.5
0
0
−0.5
−20
−1
−40
−1.5
−60
−2
−2.5
−80
0.2
0.24
0.28
0.32
0.36
0.4
0.2
0.24
0.28
0.32
0.36
0.4
Time (sec)
Time (sec)
(a) Voltage tracking error
(b) Load current
Figure 4.10
Transient response when the load was changed at
t
=
0
.
301 s from the nominal load (as
in Figure 4.1) to a resistor of 50
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