# Application of a High-Power Reversible Converter in a Hybrid Traction Power Supply System
## 5 Simulation and Experiment  
### DC Short-Circuit Fault Simulation  
A simulation model was built according to the reversible converter circuit topology in Figure 6, and the specific parameters are shown in Table 1.  
Figure 11: The stage of uncontrolled rectification.  
Due to the fact that the location of the short-circuit point is unpredictable, the simulation study is carried out in two situations, which are called proximal short-circuit (PSC) and remote short-circuit (RSC). Suppose the resistance of the overhead contact line is \(r_{1}\) = 0.028 \(\Omega\)/km, the inductance of that is \(l_{1}\) = 2.6629 mH/km, the resistance of the rail is \(r_{2}\) = 0.023 \(\Omega\)/km, the inductance of the rail is \(l_{1}\) = 1.78 mH/km. Thus, the equivalent line resistance is \(r\) = \(r_{1}\) + \(r_{2}\) = 0.051 \(\Omega\)/km, and the equivalent line inductance is \(l\) = \(l_{1}\) + \(l_{1}\) = 4.4429 mH/km.  
Related parameters and calculated results of PSC are shown in Table 2.  
Simulation results of the PSC are shown in Figures 12 and 13:  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Items** & **Values** \\ \hline AC input voltage \(V_{\text{n}}\) & 450 V \\ DC output voltage \(V_{\text{d}}\) & 750 V \\ AC side inductor \(L_{\text{r}}\) & 300 \(\mu\)H \\ DC Capacitance \(C\) & 36 mF \\ Capacitance parasitic resistance \(R_{\text{c}}\) & 0.02 m\(\Omega\) \\ Equivalent internal Resistance of diode \(R_{\text{on}}\) & 0.3 m\(\Omega\) \\ Rated power \(P\) & 1 MW \\ Switching frequency \(f_{\text{s}}\) & 2 kHz \\ \hline \hline \end{tabular}
\end{table}
Table 1: Converter parameters for the simulation. AC: alternating current; DC: direct current.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Items** & **Values** \\ \hline Short-circuit distance \(x\) & 10 m \\ Line resistance \(R\) & 0.51 m\(\Omega\) \\ Line inductance \(L\) & 0.044 mH \\ Theoretical discharge time of capacitance \(t_{1}\) & 1.9 ms \\ Theoretical peak current inductance \(i_{\text{L}}(t_{1})\) & 23,000 A \\ Theoretical period component amplitude of short-circuit current \(I_{\text{m}}\) & 3886 A \\ \hline \hline \end{tabular}
\end{table}
Table 2: Related parameters and calculated results for proximal short-circuit (PSC).  
Figure 12: DC inductor current and capacitor voltage for proximal short-circuit (PSC).  
The simulation results and the theoretical calculation results are compared in Table 4.  
From the comparisons in Table 4, some conclusions can be obtained. When the RSC occurs, the simulation results basically agree with the theoretical calculation results. However, when the RSC occurs, there are greater differences between simulation results and theoretical results. The reason is that the discharge current of the DC capacitor in RSC is smaller than the current that is provided by the AC system, so when the capacitor discharge is finished, the DC inductor current has not reached its peak value, but continues to increase slowly to the steady state short current.  
It is known from the above comparison that the peak short-circuit current in PSC is larger, and the rise is also faster, so it will do greater harm to semiconductor devices. In order to protect the reversible converter effectively, the PSC should be seriously considered.