## 4 Simulation Results
The proposed LVRT control strategy complies with the LVRT requirement, and the three-phase grid currents (\(I_{R}\), \(I_{S}\), and \(I_{T}\)) maintain a sinusoidal waveform, as shown in Figure 11d. In this paper, an additional simulation was performed to analyze the variations of the PCC voltage depending on the phase of the reactive current injected into the three-phase grid. Figures 12 and 13 show the simulation results of the PCC voltage depending on the phase of the reactive current when the ESS operates under the discharging and charging conditions, respectively. In Figures 12 and 13, the magnitudes of \(V_{R}\), \(V_{S}\), and \(V_{T}\) are decreased to 60% as compared with those of phase voltages under normal conditions. Therefore, \(I^{*}_{de}\) was determined to 80% (approximately 8.56 A) of \(I_{Inting}\) in the grid-connected ESS through the proposed LVRT control strategy. \(I^{*}_{qe}\) as the reference active current is calculated according to (1) as approximately 6.42 A. The \(I_{qe}\) values as shown in Figures 12c and 13c are controlled by \(I^{*}_{qe}\) (6.42 A in Figure 12c and \(-\)6.42 A in Figure 13c), depending on the operating conditions of the ESS, such as the discharging and charging conditions. Figure 10: Simulation results of the voltage-level calculation process that uses the three-phase grid voltages. (**a**) Three-phase grid voltages and magnitude; (**b**) Voltage-level of the three-phase grid. Figure 11: Simulation results of the proposed LVRT control strategy depending on the detecting the LVRT requirement based on the voltage-level. (**a**) Voltage-level of the three-phase grid; (**b**) Synchronous reference frame \(d\)-axis current and reference current; (**c**) Synchronous reference frame \(q\)-axis current and reference current; (**d**) Three-phase grid currents. Figure 12: Simulation results of the PCC voltage depending on the phase of the reactive current when the ESS operates under the discharging condition. (**a**) PCC voltage; (**b**) Synchronous reference frame \(d\)-axis current and reference current; (**c**) Synchronous reference frame \(q\)-axis current and reference current; (**d**) Three-phase grid currents. As shown in Figures 12b and 13b, the inductive reactive current is injected into the three-phase grid during the interval from 0.3 to 0.5 s, and the capacitive reactive current is injected during the interval from 0.5 to 0.7 s. Depending on the phase of the reactive current injected into the three-phase grid, the PCC voltage (\(V_{\mathrm{PCC}}\)) is changed as shown in Figures 12a and 13a with an extended simulation waveform. Regardless of the operating conditions of the ESS, the \(V_{\mathrm{PCC}}\) magnitude is higher when the capacitive reactive current is injected as compared with the \(V_{\mathrm{PCC}}\) magnitude when the inductive reactive current is injected. Therefore, when the grid voltage drops, the capacitive reactive current determined by the proposed LVRT control strategy needs to be injected into the three-phase grid. This contributes to the PCC voltage increase. The three-phase grid currents (\(I_{R}\), \(I_{S}\), and \(I_{T}\)) are shown in Figures 12d and 13d. Figures 14 and 15 show the simulation results of the active and reactive currents of the grid-connected ESS depending on the SOC under discharging and charging conditions. In the discharging and charging conditions of the grid-connected ESS, the proposed LVRT control strategy is applied when the grid voltage drops. However, in Figure 14, the SOC of the battery in the DC-link is changed from 20 to 10 at 0.3 s. It is lower than designated value, which is decided to 15. Additionally, in Figure 15, the SOC of the battery is changed from 80 to 90 at 0.3 s. It is higher than designated value, which is decided to 85. Fundamentally, the SOC of the battery cannot change as immediately as a step function because it is a dynamic variable. However, it was simulated to show the performance of the proposed algorithm depending on the SOC of the battery.