Environmental Engineering Reference
In-Depth Information
Fig. 1.7 Block diagram of
the grid-side converter
controller
v
dg
*
v
dg
v
dg
set
i
dg
PI5
+
+
_
_
ω
e
L
filt
i
qg
i
dg
v
dc
v
qg
*
v
qg
v
qg
set
PI6
i
qg
+
+
_
+
i
qg
ω
e
L
filt
i
dg
B. Grid-side converter controller: Fig.
1.7
shows a block diagram of the grid-side
converter controller module, which also includes two internal PI controllers PI5
and PI6, with corresponding de-coupling terms between the d and q axes.
The voltage equation for the grid-side converter RL-filter can be expressed as
di
dg
dt
¼
v
d1
R
filt
i
dg
þ
x
e
L
filt
i
dg
L
filt
x
b
di
qg
dt
¼
v
q1
R
filt
i
qg
x
e
L
filt
i
dg
ð
1
:
11
Þ
L
filt
x
b
from which the transfer function from the filter voltage to current is
T
I
dg
ðÞ
V
d1
ðÞ
I
qg
ðÞ
V
q1
ðÞ
¼
ð
1
:
12
Þ
T
1
R
filt
þ
sL
filt
=
x
b
1
R
filt
þ
sL
filt
=
x
b
ð
Þ
ð
Þ
The inputs to the grid-side controller are the set-values for the currents, which
flows to the grid through the VSC. The set-values of the input currents are cal-
culated by the active and reactive power commands P
set
s
and Q
set
g
as follows:
"#
¼
"
#
1
"#
i
set
qg
i
set
dg
P
set
s
Q
set
g
v
q1
v
d1
ð
1
:
13
Þ
v
d1
v
q1
where P
set
s
g
are the set-points of the active and reactive power commands.
The value for P
se
s
is provided by the dc-link controller, which determines the flow
of active power and regulates the dc-link voltage by driving it to a constant
reference value.
and Q
set
C. DC-link dynamic model and its controller: The capacitor in the dc-link is an
energy storage device. Neglecting losses, the time derivative of the energy in
this capacitor depends on the difference in the power delivered to the grid filter,
