ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...

4. MODELING OF PROPOSED DVR Mustafa İNCİ
4.3.2. Voltage Injection Strategy
Voltage sag and swell problems have several characteristic properties which
must be compensate. Sag/swell magnitude and phase jump problem are the most
important problems in sensitive loads. Therefore, the voltage injection strategies
must be applied depend upon these major issues.
The standard solution for compensating voltage sags is to reestablish the
exact voltage before the sag. Therefore, the amplitude and the phase of the voltage
before the sag have to be exactly restored. The resulting vector is shown in Figure
4.16.(Meyer et al., 2008)
Figure 4.16 Phasor diagram of Pre-Sag Compensation methods
In PSC method, determining pre-sag angle (θ presag ) is determined by using a
phase freezer unit. In literature, conventional phase freezer unit is created by
measuring the supply voltage (V s ) and freezing the phase angle of the supply voltage
when sag occurs. The phase angle of the supply voltage is used as the reference
phase angle of the load voltage (V l ) during sag operation as seen in Figure 4.17
(Delfino et al.,2005; Nielsen et al.,2004; Vilatgamuwa et al.,2002; Ajaei et al.,2011;
Köroğlu,2012).
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