ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...

4. MODELING OF PROPOSED DVR Mustafa İNCİ
Figure 4.12 shows that the unbalance voltage sag/swell in three phase systems
are detected to compansate unbalance voltage sag/swell seperately.
dqc f
V
dqa f
Vdqb,
f
,
, and
V ,
are severally filtered by low-pass filter for component elimination. Finally,
the filtered
V
dqa, f
Vdqb,
f
, Vdqc,
f
, are finally compared to a dc reference in comparator.
The comparator output is a sag/swell signal, which initiates a voltage sag/swell
compensation process when the voltage sag/swell occurs.
4.3.1.3. SOGI-PLL
Signals of the electrical utility grid are usually corrupted by noise and
harmonics. One way to remove these interferences is to apply filters. Either fixed or
adaptive filters can be used to fulfill the above purpose. Yet, the design of fixed
filters requires prior knowledge of both the signal and the noise, which may be
difficult to obtain, especially when the three-phase grid is subjected to unbalanced
faults. On the other hand, adaptive filters are able to adjust their impulse responses
automatically according to the output signal of the filters, and their designs require
less knowledge of the source signals or noise characteristics. This property of
adaptive filters has made them highly useful for a variety of applications. For PLL
applications, the adaptive filtering technique is employed mainly for noise reduction
and quadrature signal generation, as is illustrated in the following example(Gao et
al.,2012).
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