Page 155 - Hybrid-Renewable Energy Systems in Microgrids

Study of control strategies of power electronics during faults in microgrids 139

Figure 7.12 Power generations of VSI and the utility grid in grid-connected mode.

Figure 7.13 Three-phase voltage and frequency measured at Bus 5 in grid-connected
mode.

5.3 Performance under unbalanced faults
This section examines the short-circuit behavior of the microgrid subject to unbal-
anced faults under both grid-connected and island mode. It is assumed that all VSIs
try to inject the same amount of active and reactive power as prefault conditions. If
the converter peak current limit is reached in any phase, the corresponding VSI will
curtail its active power delivery to comply with the current limit in each phase. When
the microgrid is operating under grid-connected mode, the utility grid is the main
source of short-circuit current, which is much higher than that from VSIs. Therefore,