Arm Inductance Impact on Switched Capacitor Modular Multilevel Converter for Quasi Square Wave Modulation Regarding Voltage Mismatch

The modular multilevel DC transformer (MMDCT) is served as a crucial part in MVDC and HVDC networks. This article initially expands on the soft-switching analysis by considering practical cases, offering an in-depth investigation into switching behavior when there are time delays between arm switchings. This highlights the necessity of adding arm inductance in order to smooth arm current and reduce switching losses. Furthermore, this article presents a detailed transient analysis model of MMDCT arm current based on RLC equivalent circuit, which contributes to a more accurate component sizing according to voltage and current overshoot. The validity and switching improvement of applying proposed component design are verified through simulation and experiments with a scaled MMDCT prototype.