Solid State Transformer for Medium Voltage Grid Applications Enabled by 10 kV SiC MOSFET based Three-Phase Converter Systems

The emergence of wide bandgap semiconductors in power electronics has made it possible to manufacture medium voltage (MV) devices with low on-state resistance and offer fast switching transitions. This has enabled high switching frequencies in MV applications, which reduces the size and weight of the magnetic components and has opened up many opportunities in the field of power transmission and distribution. With the increasing popularity of MVac and MVdc microgrids, it has become necessary to have suitable MVac/MVdc, MVac/MVac, or MVac/LVac converters to integrate MVac systems with AC or DC microgrids. On account of this, an MV solid-state transformer (MV-SST) enabled by 10 kV SiC MOSFETs is developed to integrate an MV grid of 4.16 kV to a low voltage (LV) grid of 480 V. The MV-SST is divided into three stages: MVac/MVdc stage, MVdc/LVdc stage, and LVdc/LVac stage. These three stages ensure an SST operation to integrate MVac and LVac grids and provide an option to integrate DC loads or DC grids at the DC ports. This paper discusses the design, development, and operation of the 10 kV SiC MOSFETs based SST. A concise description of the hardware challenges in developing the MV-SST system is also shown. A brief description of the design aspects of different parts of the system (MVac/MVdc stage, MVdc/LVdc stage, and LVdc/LVac stage) is highlighted. Stability analysis for integrating the different converter systems is also provided to ensure that the system remains stable in its rated operating conditions. The operation and feasibility of the MV-SST system are demonstrated by experimental results.