Environmental Engineering Reference
In-Depth Information
As shown in Fig.
1.2
, the grid-side converter is connected to the grid through
the filter. The voltage equations for the RL-filter in the dq-synchronous reference
frame can be derived as shown in Sect.
2.6
.
1.2.6 RL-Filter on the Grid-Side Converter
L
filt
x
b
di
dg
dt
¼
v
d1
R
filt
i
dg
þ
x
e
L
filt
i
qg
ð
1
:
8
Þ
L
filt
x
b
di
qg
dt
¼
v
q1
R
filt
i
qg
x
e
L
filt
i
dg
where subscript filt stands for filter.
1.2.7 Voltage Source Converter Controller
Figure
1.4
presents the detailed block diagram of the VSC controller depicting the
respective input and output variables. Here, P
set
g
is the set-value for the active
power for the WT terminal. The value of P
se
g
is determined from the WT energy-
harvesting characteristic as shown in Fig.
1.5
, which is represented here as a
lookup table P
se
g
ð
x
r
Þ
determined in terms of generator rotational-speed x
r
. Since
variable-speed WTs are traditionally operated in PFC mode to achieve the unity
power factor at the terminal of the WT, the reactive power set-point Q
set
g
is set to
zero.
The VSC control module consists of the generator-side, the dc-link, and the
grid-side converter controller. These controllers utilize proportional-integral (PI)
controllers. These PI controllers are tuned using the Nyquist constraint technique
to deal with model uncertainties [
21
,
22
]. Each of the controllers is briefly
described below.
v
dq,g
v
dq,s
v
dc
v
dc
Q
g
set
P
g
set
Q
s
set
Grid-side
controller
Generator-side
controller
DC-link
controller
set
i
dq,g
P
s
P
s
set
v
dc
ref
v
dq,g
i
dq,g
P
g
Q
s
i
dq,s
ω
e
ψ
dq,s
L
filter
ω
e
Fig. 1.4
Block diagram of the VSC controller showing the input/output variables
