## 4 Result
### Test Results of LV Loads  
The load test for the STPC was configured as shown in Figure 13. Although the test system in Figure 13 produces a three-phase output, the analysis primarily focused on the unbalance caused by single-phase loads distributed across the phases, as well as the impact on other lines [25]. Figure 12: Simulation results of STPC fault current. Figure 13: Diagram of single-phase load testing. Household appliances are typically single-phase loads. While the output of the STPC provides a three-phase voltage, it can also accommodate single-phase loads; therefore, household loads were connected to each phase separately. The test loads included televisions, lighting devices, and heating equipment. In addition to residential appliances, single-phase industrial loads such as compressors and welders were also connected. Although welders are not typically considered household appliances, and guidelines from KEPCO recommend connecting them through a dedicated transformer, they were included in the test to examine their impact on other loads [24]. Each phase of the STPC was connected to a single-phase load. Specifically, electric heater and compressor loads were connected to the R-N phase, the welding machine was connected to the S-N phase, and the electronic heater, television, and lighting loads were connected to the T-N phase. The test results are illustrated in Figure 14.  
Except for the S phase, to which the welding machine was connected, the voltage and current in the other phases remained stable. In the S phase, a significant change in current was observed, while the voltage remained within the specified limits, and the connected loads operated normally. The THD also showed a significant increase only in the S phase, with no noticeable impact on the other phases. These results confirm that the load unbalance and distortion in one phase had a minimal effect on the performance of the other phases in the STPC. The detailed THD measurement results for voltage and current are presented in Table 5.  
Figure 15 presents the input and output voltage and current waveforms for a nonlinear load rated at 3 kVA. As shown in the figure, the voltage waveform remains sinusoidal, while the current waveform varies according to the characteristics of the load. In the case of nonlinear loads, only the current waveform is affected, with no significant impact observed on other loads or the STPC. These results indicate that the STPC maintains a stable operation even under nonlinear loading conditions. Figure 14: Test results of single-phase load testing. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & \(\mathbf{V_{THD\text{-}R}}\) & \(\mathbf{V_{THD\text{-}S}}\) & \(\mathbf{V_{THD\text{-}T}}\) & \(\mathbf{I_{THD\text{-}R}}\) & \(\mathbf{I_{THD\text{-}S}}\) & \(\mathbf{I_{THD\text{-}T}}\) \\ \hline THD & 0.66\% & 4.62\% & 0.33\% & 8.32\% & 92.63\% & 11.10\% \\ \hline \end{tabular}
\end{table} 
Table 5: THD measurements for each phase. For the induction motor load, a DOL motor without inverter control functionality was considered. Induction motors typically exhibit a high inrush current during startup, which can significantly affect upstream power equipment and the connected PDS, often resulting in voltage drops. Therefore, an experimental analysis of motor loads was necessary [21]. Although methods such as soft starters and capacitor banks are commonly used to mitigate motor inrush current, these techniques are not suitable for the STPC, as it operates as a grid-connected power conversion system supplying multiple loads [26]. While some large manufacturers provide inrush current specifications for motor loads, such data are not always available. Table 6 presents typical starting current values based on motor ratings. It should be noted that efficiency, power factor, and rated current values are based on 100% load conditions, and these characteristics may vary depending on the manufacturer. A motor load was required for the test.