**8. Conclusions**

In the present work, the calculation of the cell losses for Modular Multilevel Converters (MMCs) equipped with half-bridge modules, each directly connected to an elementary electrochemical cell and driven by Nearest Level Control (NLC), has been generalized for any common mode voltage value. It was observed that the total cell losses of both a Single Star MMC and a Double Star MMC are significantly higher than those occurring in an equivalent VSI.

The novel analytical investigation allowed the development of an optimal common mode voltage injection law that minimizes the cell power losses under all balanced operating conditions. The proposed method delivers a significant reduction in cell losses, which is dependent on the converter working condition and, in particular, is about 17.5% in the worst case.

All of the analytical derivations have been validated by means of an experimental set-up based on a two-arm SS-MMC with 12 modules per arm, showing an error within 2.5% in all the considered cases and confirming the effectiveness of the proposed technique, with a cell loss reduction of about 45% in the performed tests.

In conclusion, in comparison with conventional VSI solutions, MMC solutions show intrinsic advantages (modularity, BMS functionality, fault tolerance, reduced EMI issue, etc.), but are characterized by higher cell losses, which represent an important fraction of the total losses. The proposed optimum common mode voltage injection law introduces a significant reduction of the converter losses, making MMCs more attractive with respect to conventional power converters.

**Author Contributions:** Conceptualization, G.B. and I.S.; methodology, D.R. and I.S.; software, E.C.; validation, D.R. and G.B.; formal analysis, D.R.; investigation, E.C. and I.S.; data curation, G.B. and E.C.; writing—original draft preparation, G.B., E.C. and I.S.; writing—review and editing, D.R.; supervision, I.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
