## 5 Experiment Results  
To verify the validity of the proposed LVRT control strategy and analyze the variations of the PCC voltage, experiments were performed using the experimental setup as shown in Figure 16. In the experimental setup, the DC power supply (TC.GSS.20.600.4 WR.S) that has characteristic of the bidirectional power flow is used for the battery as shown in Figure 4. The experimental setup comprised a DC-link, control board, relay, switched mode power supply (SMPS), fan, power board, and magnetic contactor. The SMPS supplies the power to operate the control board and power board. The control board comprised a digital signal processor that used TMS320F28335, and the power board consisted of an inverter stage using the IGBTs and gate drivers. The parameters of the experiment were equal to those of the simulation listed in Table 1.  
Figure 17 shows the experimental results of the voltage-level calculation process. Under normal conditions, \(V_{R}\) as the \(R\)-phase grid voltage is 60 Hz/310 V\({}_{\text{peak}}\). However, in Figure 17, the grid voltage drops. The \(V_{R}\) magnitude decreases from 100% to 80% and further to 60% and 40%; subsequently, it increased to 70% and 100% as compared with the phase voltage magnitude under normal conditions. \(V_{mag}\) as the magnitude of the three-phase grid voltages is precisely calculated. In addition, \(V_{LEVEL}\) is determined, and it was used for detecting the LVRT requirement. Figure 16: Experimental setup. Figure 17: Experimental results of the voltage-level calculation process. In a scenario similar to that shown in Figure 17, the experimental results of the proposed LVRT control strategy depending on the detecting the LVRT requirement are shown in Figure 18. In Figure 18, \(I_{de}\) and \(I_{qe}\), which are the reactive and active currents, respectively, are changed by the detecting the LVRT requirement using \(V_{LEVEL}\) and the proposed LVRT control strategy. When \(V_{LEVEL}\) is 80%, \(I_{de}\) is injected into the three-phase grid with 40% of \(I_{nting}\) as the rating current in the grid-connected ESS. If \(V_{LEVEL}\) is lower than 50%, \(I_{de}\) is determined to 100% of \(I_{nting}\). In addition, \(I_{qe}\) is determined by \(I_{de}\) and \(I_{nting}\) after determining \(I_{de}\) using the proposed LVRT control strategy. As a result, when the grid voltage drops, the proposed LVRT control strategy complies with the LVRT requirement, and \(I_{R}\) as the \(R\)-phase grid current is maintained in a sinusoidal waveform, as shown in Figure 18.  
Figures 19 and 20 show the experimental 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 19 and 20, the magnitudes of the three-phase grid voltages are decreased to 60% as compared with those of phase voltages under normal conditions. Therefore, \(I_{de}\) is determined to 80% (approximately 8.56 A) of \(I_{nting}\) in the grid-connected ESS using the proposed LVRT control strategy. Additionally, \(I_{qe}\) is approximately 6.42 A according to (1). Figure 19 shows that \(I_{qe}\) is maintained at 6.42 A because the ESS operates under the discharging condition. \(I_{de}\) is changed to 8.56 from \(-8.56\) A, which means that the reactive current injected into the three-phase grid is changed to the capacitive reactive current from the inductive reactive current. In Figure 20, \(I_{qe}\) is maintained at \(-6.42\) A because the ESS operates under the charging condition. \(I_{de}\) is changed similar to that in Figure 19. Depending on the phase of the reactive current injected into the three-phase grid, \(V_{PCC}\) is changed. Regardless of the operating conditions of the ESS, the \(V_{PCC}\) magnitude is larger when the capacitive reactive current is injected as compared with the \(V_{PCC}\) magnitude when the inductive reactive current is injected. In other words, the capacitive reactive current helps in increasing \(V_{PCC}\) regardless of the operation conditions.