ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...

3. FUNDAMENTALS OF DVR Mustafa İNCİ
Figure 3.14. Vector diagram of in-phase compensation
In most cases, a voltage sag leads to a phase jump, therefore the distortions
due to phase changes are not minimized. As a consequence, a phase jump will be
applied to at the load, leading to transients and circulating currents. Thus, if a
sensitive load must be secured, the in-phase compensation cannot be used, be-cause
it could lead to the tripping of sensitive loads. Note that, to realize this strategy, the
PLL has to be synchronized to the grid voltage itself, and therefore, must not be
locked to the pre-sag grid voltage during the compensation (Meyer et al., 2008).
3.3.3.3. Phase advance compensation
In this method the real power spent by DVR is minimized by decreasing the
power angle between the sag voltage and the load current. In the two previous cases,
namely pre -sag and in-phase compensation, active power is injected into the system
by the DVR during disturbances. Moreover, the active power supplied is limited to
the stored energy in the DC link and this part is one of the most expensive parts of
the DVR. The minimization of injected energy is achieved by making the injection
voltage phasor perpendicular to the load current phasor (Shazly et al., 2013).
35