## 4 Simulation Results  
In this paper, the simulation was performed before verifying the operation of the 3-phase AC/DC PWM converter with the SOGI-FLL method for the DC distributed system. Table 1 shows the parameters that are used in the simulation, while the configuration of the simulation circuit is shown in Figure 15. In the existing AC power grid, the power from the power plant is supplied to the consumer in single phase 220 V\({}_{\text{rms}}\) and 3-phase 380 V\({}_{\text{rms}}\). Therefore, the 3-phase voltage is selected, as shown in the parameter. Also, when configuring of the DC distribution system, the DC-link voltage was selected as 700 V\({}_{\text{dc}}\), which is capable of meeting the scope of international electrotechnical commission (IEC) regulations [24]. The switching frequency is selected in consideration of the FS300R12 KE3, which IGBT are used in this system, and the LCL filter are designed to satisfy the current distortion regulation of the IEEE ST 519-2014. \begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **Value** & **Unit** \\ \hline Rated power of system & 50 & [kW] \\
3 phase line-to-line grid voltage & 380 & [V\({}_{\text{rms}}\)] \\ Grid frequency & 60 & [Hz] \\ Switching frequency & 5 & [kHz] \\ Output DC-link voltage & 700 & [V\({}_{\text{dc}}\)] \\ DC-link capacitance & 10200 & [\(\mu\)F] \\ LCL filter inductance at grid side & 120 & [\(\mu\)H] \\ LCL filter capacitance & 50 & [\(\mu\)F] \\ LCL filter inductance at converter side & 500 & [\(\mu\)H] \\ \hline \end{tabular}
\end{table} 
Table 1: Simulation parameter of DC distributed system. Figure 15: 3-phase AD/DC PWM converter schematic of DC distribution system used in simulation. Figure 16a shows the output voltage waveform of a DC distribution system while using a 3-phase AC/DC PWM converter. The system uses an initial charge circuit that charges a certain amount of voltage to the output capacitor for 0.2 s to reduce the inrush current entering the output capacitor. Then, the charge of the capacitor voltage increases, while the initial charge circuit is changed from the initial charge to a standby condition. Finally, an output voltage control of 700 V\({}_{\mathrm{dc}}\) is initiated from 0.3 s. In order to prevent the high overshoot of the output voltage at the start of the control, the voltage reference is given in the form of a ramp. The voltage reference then rapidly enters the steady state due to the fast dynamic characteristics of the PI controller. Figure 16b shows the output current waveform after connecting the DC link output to the load. The load is connected to the system from 0.8 s and the load capacity is increased by 10 kW every 0.15 s. Finally, a current is stably generated at the system rated capacity of 50 kW. Figure 16c shows the 3-phase input current waveform from the grid to the system. It is confirmed that the reactive component rarely flows when no load is applied, and the magnitude of the input current increases step by step when the load is connected. Figure 17a shows the 3-phase input voltage waveforms containing the 3 rd, 5 th, 7 th, 9 th, and 11 th harmonics. The input voltage is detected through the sensor and is then input to the controller. The SOGI-FLL is applied to the system controller in the middle of the \(\alpha\beta-dq\) coordinate transformation,  
Figure 16: Input and output waveforms of DC distribution system (**a**) the dc-link voltage; (**b**) the current of the DC load; and, (**c**) the current of the grid. and the output voltage of the SOGI-FLL indicates that the harmonics are reduced, as shown in Figure 17b. The THD of the detected positive sequence voltage is about 3.9%, which is appropriate for the phase angle detection. Figure 18 shows the waveforms when a voltage drop of about 30% occurs on the \(b\) phase. Figure 18a shows the dc-link output voltage waveform. A voltage ripple of about 2 [Vpeak-to-peak] is generated while voltage drop occurs. Figure 18b shows the unbalanced 3-phase input voltage waveform.