ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...

4. MODELING OF PROPOSED DVR Mustafa İNCİ
In this equivalent circuit,
L
f
and
C
f
constitute the single section LC filter;
R
f
is used to damp the filter at the resonant frequency f 0
. V
inv
represents the output
voltage of the PWM inverter, i is the input current, a
i
c
is the capacitor current, i o
and V
o
are the output current and the output voltage of inverter side filter. Transfer
function of the LC filter is expressed as (Köroğlu, 2012);
V
1
L
f
s + R
f
s)
= V ( )
I ( s)
2 inv
s −
o
(4.4)
L C s + R C s + 1 L C s + R C s + 1
o
(
2
f f f f
f f
f
f
Figure 4.5 shows the block diagram of single phase PWM inverter side filter
according to the transfer function (Kim et al., 2000, Köroğlu, 2012).
1
L s +
f
R f
1
C f
s
Figure 4.5. Block Diagram of Single Phase PWM-VSI.
In the conventional output filter design method, the output current i is 0
treated as the disturbance and so it is neglected and the new transfer characteristic
can be rewritten as (Kim et al., 2000, Köroğlu, 2012);
Vo
( s)
H ( s)
= =
2
V ( s)
L C s
inv
f
f
1
+ R C
f
f
s + 1
(4.5)
While choosing the filtering system, the cut-off frequency f
0
of the filter
should be minimally 10 times greater then grid frequency and simultaneously
maximally one half of the converter switching frequency. The decrease of the power
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