A Methodology to Select the Number of Cascaded Cells for a Medium Voltage Multilevel AC-DC Solid State Transformer

An extreme fast charging (XFC) station, capable of simultaneously charging multiple electric vehicles (EVs), is envisioned as a replacement for a traditional gas station. A cascaded multicell AC-DC solid-state transformer (SST) is proposed for the direct interconnection of the XFC station with the medium voltage (MV) grid to achieve galvanic isolation. The efficiency implications of the multicell SST are evaluated with state of the art Silicon (Si) and Silicon Carbide (SiC) power modules. A methodology is presented to select the number of cascaded cells for such a multicell SST. It is demonstrated that SiC power modules can enable simple and efficient SST designs with a fewer number of cascaded cells as compared to an SST solution that utilizes Si IGBT based power modules.