## 2 Simplified DC Microgrid Description and System Parameters  
The configuration of the proposed small-scale multi-terminal low-voltage DC system with three small interconnected areas is shown in Figure 1. The breakers which connect the buses must open during the fault condition in any part of the interconnected lines. In each area, PV panels, loads, and the storage system, as the main components, were connected through the converters and breakers. the PV boost converter used a Maximum Power Point-Tracking-Incremental Conductance (MPPT-IC) Algorithm to track the maximum power point and deliver the maximum available power of the PV [18; 19]. The feedback PI controller was used to regulate the output voltage of the boost rectifier. Also, batteries were equipped with a DC-DC bidirectional converter to provide two-way power flow. They charged by using the surplus power generation of PV and discharging over the night and cloudy periods. The main components of the system are listed in Table 1. In this configuration, power can be shared among the neighboring areas based on the voltage deviation of each local area. We also specified some representative locations where faults (\(F_{1}\)-\(F_{3}\)) could occur in the system to evaluate the proposed protection system. Due to the effects of line impedance on the voltage drop, fault current, and fault interruption time, we considered it as a constant value. In a multi-terminal network, a consideration of CB at both ends of the line and interconnected buses are essential to prevent complete blackout by downstream short-circuit faults. Recently, the SSCB has been recognized by a key enabling technology for the DC distribution system and had the ability to interrupt the circuits under a full load within \(\upmu\)s. The regional short-circuit interruption can be perfectly obtained by integrating the CB with the related controller throughout the system [20]. The relevant electrical circuits and controllers of the converters with battery and solar panels are depicted in Figures 2-4. In Figure 4, the difference of the bus voltage (\(V_{bus}\)) and the reference value (desired bus voltage) was computed by the synchronous measurement of the bus voltage, and the mismatch converged to the desired value through two feedback PI controllers and the proper operation of the bidirectional converter.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Symbol** \\ \hline Max \(P_{PV1}\) & 20.5 kW & \(P_{PV1}\) \\ Max \(P_{PV2}\) & 31 kW & \(P_{PV2}\) \\ Max \(P_{PV3}\) & 41 kW & \(P_{PV3}\) \\ DC \(Load_{1}\) & 15 kW & \(L_{1}\) \\ DC \(Load_{2}\) & 23 kW & \(L_{2}\) \\ DC \(Load_{3}\) & 34 kW & \(L_{3}\) \\ Battery & 45 (3 \(\times\) 15) kWh & \(B\) \\ DC bus voltage & 400 V & \(V_{bus}\) \\ Feeder length & 1.5 km & \\ Switching Frequency & 5 kHz & \(F\) \\ Line Resistance & 0.14 \(\Omega\)/km & \(R\) \\ Line Inductance & 0.24 mH/km & \(L\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: System parameter and components.  
Figure 1: The single-line diagram of a DC microgrid cluster and fault locations.  
Figure 2: Circuit diagram of the boost converter and the related feedback PI controller.