ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...

4. MODELING OF PROPOSED DVR Mustafa İNCİ
Figure 4.11. Conventional SRF based detection
2
d
2
q
From Figure 4.11, V = V = V + V , this voltage varies with the grid
p
dq
voltages then the voltage sags can be detected from value of V
dq
. This V
dq
is filtered
by low-pass filter (LPF) for
2ω
or 100-Hz component elimination (for 50-Hz
distribution systems). The filtered V
dq
or V
dq , f
is finally compared to a dc reference
in comparator (i.e. 0.9 pu). The comparator output is a sag signal, which initiates a
voltage sag compensation process when the voltage sag occurs(Sillapawicharn et
al,2011).
To compensate unbalance voltage sags, three-phase symmetric voltages can
be constructed by a-phase voltage, which is carried into dq transform according to
the equation(Jianwei et al,2011):
V
a
= V
ref
n
( iy + ϑ ) + 2u
( ωiy
+ )
n
∑ u
i=
1 1i
sin
1i
∑i
=
, a
= 2 ω
2i
sin ϑ
i
(4.38)
1 2
It can be constructed for
V
ref , b
=
⎛ 2π
⎞
⎛ 2π
⎞
ω u ⎜ + + ⎟
= i i
it
1 1
2
1 2
sin ω ϑ2i
(4.39)
⎝ 3 ⎠
⎝ 3 ⎠
n
n
∑ 2u1
i
sin⎜
it + ϑ
i
− ⎟ + ∑ =
i
V
ref , c
=
⎛ 2π
⎞
⎛ 2π
⎞
ω u ⎜ + − ⎟
= i i
it
1 1
2
1 2
sin ω ϑ2i
(4.40)
⎝ 3 ⎠
⎝ 3 ⎠
n
n
∑ 2u1
i
sin⎜
it + ϑ
i
+ ⎟ + ∑ =
i
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