# Solid-State Transformer-Based DC Power Distribution Network for Shipboard Applications
## 2 DC Distribution Systems Based on Conventional and Solid-State Transformers  
The difference between the AC and DC transmission systems, depicted in Figure 2, should be considered in justifying the cost and efficiency of the SST [27]. In this regard, the \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Conventional System** & **Proposed System** \\ \hline Transformer & \begin{tabular}{c} High rating power \\ transformer \\ \end{tabular} & Less rating power transformer \\ \hline Distribution & AC & DC \\ \hline Generation & Diesel generators & Hybrid \\ \hline Main functions & \begin{tabular}{c} Voltage transformation, \\ isolation, and power \\ transmission \\ \end{tabular} & \
\begin{tabular}{c} Voltage transformation, \\ isolation, and power \\ transmission \\ \end{tabular} \\ \hline Additional functions & None &
\begin{tabular}{c} Automatic voltage regulation, \\ power factor correction, \\ power flow control, fault \\ current limitation \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Shipboard power distribution systems. system costs are higher in the case of the SST because they are compared with a mature technology, core-type transformers, while including the SST auxiliary circuit costs. In the AC transmission system, the SST possesses a higher cost, lower efficiency, and higher circuit footprint as it employs two converters at each side of the SST. Conversely, the core-type transformer does not require any interfacing components to perform voltage regulation and, therefore, is more advantageous in terms of system reliability, compatibility, and efficiency. However, in DC transmission systems, the traditional transformer requires three-phase converters to eventually realize the voltage regulations, which contribute to more bulky system requirements to accommodate the full power for the system, as shown in Figure 2. On the other hand, the DC distribution system based on SST requires fewer semiconductor devices, gate drivers, and heat sinks to achieve the same goal with a more compact system. Thus, in a DC distribution system, the system based on SST is more advantageous than the core-type counterpart since it offers higher efficiency and potentially reduced costs. Table 2 reveals the key differences in the DC transmission system in the case of utilizing core-type and solid-state transformers [28; 29; 30]. According to the extensive analysis of advanced shipboard power electronics carried out in Ref. [28], the SST technology maturity is yet to gain more momentum when compared to its core-type counterparts. Efficiencies up to 98% have been obtained and further enhancements are expected owing to the utilization of the wide-bandgap semiconductors, e.g., silicon carbide (SiC), which alleviate an improved power conversion system with smaller size and lower loss. Moreover, SiC MOSFETs are favorable since they are suitable for high frequency operation with fast switching capability and minimum switching loss [29]. Based on the conducted discussion, the solid-state transformer has proved to offer a \begin{table}
\begin{tabular}{l c c} \hline \hline  & **Core-Type Transformer** & **Solid-State Transformer** \\ \hline Converter rating & Full power rating & Cascaded and multilevel topologies at lower ratings \\ \hline \multirow{4}{*}{Semiconductor devices count} & 12 & 8 \\  & (in case of utilizing three-phase PWM back converters) & (in case of utilizing full power rated H-bridges and higher rated converters for MMC topologies) \\ \hline Overall system efficiency range & 88–92\% & \textgreater{}95\% \\ \hline Transformer power density & 0.2–0.35 kVA/kg & 0.5–0.75 kVA/kg \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison between the DC distribution systems based on conventional and solid-state transformers. Figure 2: Transmission systems based on core-type and solid-state transformer. multitude of merits and functionalities in DC grid applications in general and, particularly, traction ones. Therefore, this study proposes a smart SST using the latest SiC technology.