## 7 Simulation Assessment
### Performance of the Separated Phase-Current Controls Using IBDGs
#### 7.2.1 Temporary SLG Fault
As shown in Figure 12a,b, the IBDGs injected the active current into phases \(a\) and \(c\). In the faulty phase, the fault and the connection of SDG were detected. The FIM strategy was enabled at 0.155 s to remove the effects of fault current contribution from the SDG. The active and reactive currents behaved rather arbitrarily because the current reference was computed by Equation (12), which is derived from the fault current, where the \(V_{dc}\) and grid voltage are not considered. As shown in Figure 12a,b, IBDG1 absorbed the active current from phase \(b\), while IBDG2 injected the active current into phase \(b\). After the tripping event of the recloser at 0.406 s, the FIM strategy was changed to an islanding strategy because the recloser sent a tripping signal to the IBDGs. In other words, no IBDG supplied the active and reactive currents to phase \(b\). This action prevented the damage caused by out-of-phase reclosing. The \(P\) and \(Q\) of all IBDGs can be seen in Figure 12c. Due to the active current injection, all IBDGs could inject the active power into the grid during a fault. The benefit of the voltage regulation feature is demonstrated in Figure 13 for the three-phase voltages at node 862, where the voltage regulation feature was disabled and enabled. During a ground fault, the grid overvoltage of the nonfaulty phase could occur due to the system grounding. In Figure 13a, the grid voltage in phase \(c\) was increased over the upper permissible voltage limit of 1.1 pu since the voltage regulation feature was disabled. When the voltage regulation feature was turned back on, all of the IBDGs compensated for the grid overvoltage of phase \(c\) by absorbing the reactive current, as shown in Figure 12a,b. The reactive current of phase \(c\) drawn by IBDG2 increased. Because the difference between \(V_{d}\) of IBDG1 and the upper permissible voltage limit was small, the IBDG1 consumed a low reactive current from phase \(c\). Although the grid overvoltage of phase \(c\) was reduced, it was still higher than the upper permissible voltage limit, as shown in Figure 13b. Figure 11: Conventional current control during temporary SLG fault: (**a**) active and reactive currents of IBDG1; (**b**) active and reactive currents of IBDG2; and (**c**) average powers of all IBDGs. At 0.2268 s, the voltage selector of IBDG1 switched the input of the voltage regulator from \(V_{d}\) of IBDG1 to \(V_{d}\) of IBDG2. The reactive current of phase \(c\) consumed by IBDG1 increased. Accordingly, the grid overvoltage of phase \(c\) could be compensated for at around the upper acceptable voltage limit. From the reactive power relationship (\(Q=-0.5V_{d}l_{q}\)), the reactive power flowed from the grid to the IBDGs when the reactive current was controlled as positive, meaning that the reactive current consumed by the IBDGs was of a positive quantity. Figure 12: Separated phase–current controls during temporary SLG fault: (**a**) active and reactive currents of IBDG1; (**b**) active and reactive currents of IBDG2; and (**c**) average powers of all IBDGs. Figure 13: RMS voltage at node 862 during temporary SLG fault: (**a**) disabled voltage regulation feature; (**b**) enabled voltage regulation feature.