## 5 Experimental Verification  
The simulation model of the DC microgrid built using PSCAD/EMTDC is shown in Figure 5. At the sending ends, the transmission terminal is in constant power (PQ) control mode and the receiving terminal is in constant DC voltage (\(U_{dc}\)) control mode. The DC microgrid voltage is 1.2 kV and the transmission power is 0.5 MW [25; 26]. The parameters and cable lengths of each element are shown in Table 1. A DC cable and bipolar connections were used. The DC arc current is nonlinear; changes in amplitude are not obvious at HRF. The amplitude frequency variations of various arc currents are shown in Figure 6. As the arc current increases, so too does the high-frequency component; the current amplitude \begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Value** \\ \hline DC line voltage & 1.25 kV \\ Cable resistance & 0.02 ohm/km \\ Cable inductance & \(7.68\times 10^{-6}\) H/km \\ \hline \end{tabular}
\end{table} 
Table 1: DC microgrid model parameters. Figure 4: Flow chart of arc resistance detection. Figure 5: A two-port DC microgrid. decreases when the frequency increases. The frequency-domain characteristics of arc current were directly related to the amplitude. When the amplitude is low, the frequency fluctuates. Therefore, the Cassie model can represent a DC arc under a low arc current. The arc resistance current depends on the arc voltage. During simulation, the arc current was affected mainly by the grounding point in series with the arc resistance. The fault time was 3 s, the arc resistance ground connection was 100 ohm, the fault distance was 1 km, and the interaction voltages were 160 and 200 V. The amplitude and frequency characteristics of the normal and line currents grounded by the arc resistance are shown in Figure 7.  
Comparison of Figure 8a,b shows that, after grounding, the frequency amplitudes at lower layer increased, as did the arc voltages. The amplitudes of the line current changes were in line with this analysis. Time-based frequency-domain analyses are commonly used to explore arc resistance grounding, with wavelet decomposition then applied to extract the characteristics thereof. Analysis of the detail wavelet coefficients is preferred via decomposition to five layers, of which d5 is the special frequency layer (in which arc current amplitudes typically increase). This layer yields valuable information about arc frequency decomposition. The decomposed fault current is shown in Figure 8.  
Figure 6: The DC arc current spectrum. Figure 7: Amplitude frequencies of the normal and arc-resistance grounding fault currents: (**a**) Normal current amplitudes and frequency characteristics; (**b**) amplitude frequency characteristics when the inter-arc voltage was 160 V and the grounding resistance was 100 ohm; (**c**) amplitude frequency characteristics when the inter-arc voltage was 200 V and the grounding resistance 100 ohm. Wavelet decomposition does not directly yield frequency data. Thus, after collecting the decomposition data of all components of the frequency domain, The Hankel matrix was constructed and subjected to SVD, which yielded normal and arc currents with 30 single values (Figure 9). The singular value arrangement was guided mainly by the wavelet decomposition scale scores, using a5 as the feature contrast sequence. The effect of the arc current was then apparent; the top 10 a5 singular points on the fault current SVD decomposition graph exhibited obvious amplitude changes, reflecting the amplitude of the DC low-frequency band and low arc current amplitude. Figure 10 shows the result of fault signal after denoising the specified converter switching frequency and the background noise. Table 2 shows the time-domain data for different fault situations. The detection threshold was selected based on the normal current value, i.e., 27.