## 2 Modular Multilevel Converter and Sub Module Variants
Even though it has more components, it lacks the dc-link short circuit handling capability, which results in severe control losses [17]. Two FBSMs are connected, as shown in Figure 3c, for improving the capacitor voltage performance, while keeping their SM's power level the same. This configuration [23] double-submodule (DSM) can improve the \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sub-Module (SM)** & **NVL** & **Voltage Level** & **NS** & **MNSC** & **MBV** & **Bipolar** &
\begin{tabular}{c} **DC-Fault** \\ **Handling** \\ \end{tabular} \\ \hline Two-Level SMs & & & & & & & \\ \hline HBSM & 2 & 0, +V\({}_{\text{C1}}\) & 2 & 1 & V\({}_{\text{C1}}\) & No & No \\ \hline Unipolar SM & 2 & 0, +V\({}_{\text{C1}}\) & 3 & 1 & V\({}_{\text{C1}}\) & No & Yes \\ \hline Unidirectional & 2 & 0, +V\({}_{\text{C1}}\) & 1 & 1 & V\({}_{\text{C1}}\) & No & No \\ \hline CSSM & 2 & 0, +V\({}_{\text{C1}}\) & 3 & 2 & V\({}_{\text{C1}}\) & No & Yes \\ \hline Three-Level SMs & & & & & & & \\ \hline FBSM & 3 & 0, +V\({}_{\text{C1}}\), \(-\)V\({}_{\text{C1}}\) & 4 & 2 & V\({}_{\text{C1}}\) & Yes & Yes \\ \hline TLFCSM & 3 & 0, +V\({}_{\text{C2}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 4 & 2 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & No & No \\ \hline TLNPC-1 & 3 & 0, +V\({}_{\text{C2}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 4 & 2 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & No & No \\ \hline TLNPC-2 & 3 & 0, +V\({}_{\text{C2}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 6 & 2 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & No & No \\ \hline TLNPC-3 & 3 & 0, +V\({}_{\text{C2}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 4 & 2 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & No & No \\ \hline DSM & 3 & 0, +V\({}_{\text{C2}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 8 & 4 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & No & Yes \\ \hline TLCCSM & 3 & 0, +V\({}_{\text{C2}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 5 & 3 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & No & Yes \\ \hline DBSM & 3 & 0, +V\({}_{\text{C1}}\), \(-\)V\({}_{\text{C2}}\) & 2 & 1 & V\({}_{\text{C1}}\) & Yes & Yes \\ \hline IHSM & 3 & 0, +V\({}_{\text{C1}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 5 & 3 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & No & Yes \\ \hline Four-Level SMs & & & & & & \\ \hline CDSM-1 & 4 & 0, +V\({}_{\text{C1}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 5 & 3 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & Yes & Yes \\ \hline CDSM-2 & 4 & 0, +V\({}_{\text{C2}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 7 & 3 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & Yes & Yes \\ \hline Asymmetrical & 4 & 0, +V\({}_{\text{C2}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 4 & 2 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & Yes & Yes \\ \hline Mixed SM & 4 & 0, +V\({}_{\text{C2}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 6 & 3 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & Yes & Yes \\ \hline SDSM & 4 & 0, +V\({}_{\text{C2}}\), +(V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 5 & 3 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & Yes & Yes \\ \hline Five-Level SMs & & & & & & \\ \hline FLCCSM & 5 & 0, +V\({}_{\text{C1}}\), +V\({}_{\text{C2}}\), \(\pm\)(VC\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 6 & 3 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & Yes & Yes \\ \hline CCSM & 5 & 0, +V\({}_{\text{C1}}\), +V\({}_{\text{C2}}\), \(\pm\)(VC\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 8 & 4 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & Yes & Yes \\ \hline PCSM & 5 & 0, +V\({}_{\text{C2}}\), \(\pm\)(VC\({}_{\text{C1}}\) + V\({}_{\text{C2}}\)) & 8 & 4 & V\({}_{\text{C1}}\) + V\({}_{\text{C2}}\) & Yes & Yes \\ \hline \hline \end{tabular} Note: SM—Submodule, NVLs—Number of Voltage Levels, NSs—Number of Switches, MNSC—Maximum Number of Switches in the Conduction Path.  
\end{table} 
Table 1: Comparison of different submodules [13; 14; 15; 16; 17; 18; 19; 20]. functionality of the SM without an increment in the semiconducting device's cost.