ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...

4. MODELING OF PROPOSED DVR Mustafa İNCİ
control transient as well as steady-state behavior of the filter. This feature of the
filter, as it is shown in this paper, makes it suitable for a variety of
applications(Karimi et al, 2002).
4.3.1.2. Synchronous Reference Frame (SRF)
This algorithm is based on obtaining the equivalent space vector of three
phase quanitities(Meena et al, 2012).The three supply phases are converted into one
phasor “ V S
” which itself is comprised of two orthogonal components " Vα
and V
β
" .
A synchronous reference frame is locked to “ V S
” via a PLL. The vectors are
generated by the following formulas (4.35) and (4.36):
⎡V
⎢
V
⎢
⎢⎣
V
α
β
0
⎤
⎥
=
⎥
⎥⎦
⎡1
2 ⎢
0
3 ⎢
⎢⎣
0
− 0.5
0.866
0
− 0.5 ⎤⎡V
− 0.866
⎥⎢
V
⎥⎢
0 ⎥⎦
⎢⎣
V
a
b
c
⎤
⎥
⎥
⎥⎦
(4.35)
⎡V
⎢
⎣V
d
q
⎤ ⎡ cosϑ
⎥ = ⎢
⎦ ⎣−
sinϑ
sinϑ
⎤⎡V
⎥⎢
cosϑ⎦⎣V
α
β
⎤
⎥
⎦
(4.36)
If the utility system operates under normal conditions, or if any balanced fault
occurs, positive sequence d–q components (Vd and Vq) are DC components. If any
unbalanced fault occurs, the resulting voltage sag/swell is unbalanced and contains
both positive sequence and 100 Hz (for 50 Hz network frequency) negative sequence
components(Tumay et al., 2009). For a positive sequence SRF, the positive sequence
component can be named as DC, and 100 Hz negative sequence component can be
named as ripple. Conventionally, to separate the DC component and ripples, a low
pass filter (LPF) is used after
p
dq
2
d
2
q
V = V = V + V operation. Nevertheless, the
‘original positive sequence component’ cannot be obtained. The filter also causes a
certain amount of delay in the error signal. Vp is used for error calculation after
separation of DC components and ripples by disturbance filters(Tumay et al,2009).
64