ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...

3. FUNDAMENTALS OF DVR Mustafa İNCİ
In (3.10), actual voltage ratio between and can be explained
N
Z
= n
2
eq eq
M
( R + jω L )( [ 1−
ω L C ) + jωR C ]
f
f
i
f
(3.10)
When the source voltage varies, is maintained by the injection voltage
from the DVR. As effective DVR voltage sag periods, the load current I
L
will
be maintained constant. Considering that the magnetization impedance
Z
M
of the
series transformer is much larger than the transformer is much larger than the
transformer series resistance and leakage reactance, it can be concluded that the
voltage drop
∆Vp
caused by the transformer is ∆ V p
= ( R eq
+ jωL
eq
) I L
, where
R
eq
2
2
= Rp
+ n Rs
, Leq
Lp
+ n Ls
= . The magnitude of the voltage drop is
( R eq
+ jωL
eq
) I L
∆ V p
=
. Clearly, ∆Vp
will contribute toward a reduction in the load
voltage. Also the associated active power loss due to the transformer
I 2
eq L
R exists at
all time. Hence to reduce the voltage drop and power loss due to the transformer it is
desirable that its short-circuit impedance
means a more costly transformer (Li et al., 2002).
R
eq
+ jωL
is kept as low as possible. This
eq
3.2.5. Filter
The semiconductor switching devices are used in wide variety of industrial
loads. The non-linear characteristics of semiconductor devices cause distorted
waveforms associated with harmonics. To overcome this problem and providing
clean electrical supply filter unit is used (Choi et al., 2002; Li et al., 2001). The
purpose of any of the filtering schemes is for the attenuation of the high-order
harmonics due to the inverter switching (Choi et al, 2000). Two filtering methods are
presented in literature: line side and inverter side.
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