Page 156 - Hybrid-Renewable Energy Systems in Microgrids

140 Hybrid-Renewable Energy Systems in Microgrids

Figure 7.14 Power generations of VSI in islanded mode.

Figure 7.15 Three-phase voltage and frequency measured at Bus 5 in islanded mode.

the control strategies using instantaneous power theory have less impact on the charac-
teristics of the short circuit current under unbalanced faults. As an example, Fig. 7.16
shows the short-circuit current leaving bus 3 when A-g and A-B fault is initiated at
0 s in the middle of line 3-4, where all three VSIs are controlled to injected balanced
current under fault conditions. The prefault conditions are kept the same as the last
section both modes.
When the microgrid is operating under islanded mode, the three VSIs become
the main sources of the short-circuit current. In the following simulations, the short-
circuit current is examined considering various prefault conditions, which includes