ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...

4. MODELING OF PROPOSED DVR Mustafa İNCİ
factor caused by the filter capacitance should be lower than 5% (Lettl et al., 2011,
Köroğlu et, 2012).
Cut off frequency f
0
should be between 500 Hz and 1500 Hz where grid
frequency is 50 Hz and PWM inverter switching frequency is 3000 Hz (Köroğlu,
2012).
f
o
1
= (4.6)
2π L C
f
f
In order to achieve the proper
L
f
and
C
f
values, this time below equations
should be satisfied (Acar, 2002; Choi et al., 2002).
K
V
THD P
V
T
= (4.7)
K
i
M
∑
n=
m
M ⎛
2
V inv n
⎞
2
( )
V ⎜
⎟
o(
n)
= ∑
< V
2
n m nwo L
f
C
= ⎝ ( )
f
−1⎠
2
T
(4.8)
V
inv
4VDC
( n)
= (4.9)
2 nπ
In Equation 4.7, V
T
is the rms value of total harmonics voltage (per phase) on
the high voltage-side of the injection transformer, K
THD
is the voltage THD for a 11
kV system which can not be greater than 5.0%, K
i
is the turns ratio of the injection
transformer, V
p
is the voltage on the high voltage side of the injection transformer.
In Equation 4.6, V
o( n)
and V
inv (n)
are the n th order harmonic voltages on the
output and input of inverter where n is the order of harmonics (n = m, m+1, m+2,....,
M). V
inv (n)
can be obtained form Equation 4.6, in which VDC
is the DC link voltage.
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