ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...
ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ... ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...
3. FUNDAMENTALS OF DVR Mustafa İNCİ If the distribution circuit is weak there is need to inject small compensation voltage to operate correctly. During short circuit operation, the injected voltages and magnetic fluxes are virtually zero thereby full load current pass through the primary. The DVR will be most of the time in normal mode operation. During standby mode normal operation), the short circuit impedance of the injection transformer determines the voltage drop across the DVR (Teke, 2005). 3.3.2.3. Injection Mode The primary function of Dynamic Voltage Restorer is compensating voltage disturbances on distribution system. To achieve compensation, three single-phase ac voltages are injected in series with required magnitude, phase and wave shape. The types of voltage sags, load conditions and power rating of DVR will determine the possibility of compensating voltage sag (Teke, 2005). 3.3.3. Voltage Injection Strategies The way in which the dynamic voltage restorer (DVR) is used during the voltage injection mode depends upon several limiting factors such as: DVR power rating, load conditions, and voltage-sag type. For example, some loads are sensitive to phase-angel jumps, some others are sensitive to a change in voltage magnitude and some others are tolerant to all these disturbances. Therefore the control strategies to be applied depend upon the load characteristics (Shazly et al., 2013). There are four different methods of DVR voltage injection strategies: • Pre-sag compensation • In-phase compensation • In-phase advanced compensation 33
3. FUNDAMENTALS OF DVR Mustafa İNCİ 3.3.3.1. Pre-sag compensation The pre-sag compensation method tracks supply voltage continuously load voltage during a fault to restore the pre-fault condition. Figure 3.13 shows the singlephase vector diagram of the pre-sag compensation. In this method, the load voltage can be restored ideally, but injected active power cannot be controlled and is determined by external conditions such as the type of faults and load condition (Quirl et al., 2006). Figure 3.13. Vector diagram of pre-sag compensation 3.3.3.2. In-phase compensation As already mentioned, the pre-sag compensation does not lead to a minimized voltage amplitude. This can be realized with the in-phase strategy, which is designed to control the DVR with a minimum output voltage. In Figure 3.14, the voltages for this strategy are depicted. In contrast to the pre-sag version, the voltage is now compensated in phase to the grid voltage after the sag. Hence, the required voltage amplitude is minimized, but the phase jump is not compensated (Meyer et al., 2008). 34
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- Page 5 and 6: ACKNOWLEDGEMENTS First and foremost
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3. FUNDAMENTALS <strong>OF</strong> DVR Mustafa İNCİ<br />
If the distribution circuit is weak there is need to inject small compensation<br />
voltage to operate correctly. During short circuit operation, the injected voltages and<br />
magnetic fluxes are virtually zero thereby full load current pass through the primary.<br />
The DVR will be most of the time in normal mode operation. During standby mode<br />
normal operation), the short circuit impedance of the injection transformer<br />
determines the voltage drop across the DVR (Teke, 2005).<br />
3.3.2.3. Injection Mode<br />
The primary function of Dynamic Voltage Restorer is compensating voltage<br />
disturbances on distribution system. To achieve compensation, three single-phase ac<br />
voltages are injected in series with required magnitude, phase and wave shape. The<br />
types of voltage sags, load conditions and power rating of DVR will determine the<br />
possibility of compensating voltage sag (Teke, 2005).<br />
3.3.3. Voltage Injection Strategies<br />
The way in which the dynamic voltage restorer (DVR) is used during the<br />
voltage injection mode depends upon several limiting factors such as: DVR power<br />
rating, load conditions, and voltage-sag type. For example, some loads are sensitive<br />
to phase-angel jumps, some others are sensitive to a change in voltage magnitude and<br />
some others are tolerant to all these disturbances. Therefore the control strategies to<br />
be applied depend upon the load characteristics (Shazly et al., 2013). There are four<br />
different methods of DVR voltage injection strategies:<br />
• Pre-sag compensation<br />
• In-phase compensation<br />
• In-phase advanced compensation<br />
33
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