Protection Scheme for a Medium Voltage Mobile Utility Support Equipment based Solid State Transformer (MUSE-SST)

In recent years, the concept of solid-state transformers (SSTs) has evolved to be one of the front runners in the development and realization of a smart grid. The recent strides in the field of medium voltage wide bandgap semiconductor devices and the availability of 10 kV SiC MOSFETs and 15 kV SiC IGBTs have made it possible to build medium voltage SSTs using simple converter topologies. With the SST interfacing two grids, it forms a crucial juncture in the electrical distribution system which necessitates a high fault tolerance capacity of the SST during grid fault conditions. In addition, the grids need to be protected from any faults or abnormal operation in the SST which makes it imperative to implement different fault protection considerations on the SST. In this paper, these fault protection systems are studied in terms of their breaking time, breaking current/voltage, and fault coordination. The protection schemes are analyzed on a Gen3 10 kV SiC MOSFETs based Mobile Utility Support Equipment Solid-State Transformer (MUSE-SST) which is developed at FREEDM Systems Center aimed at interconnecting a 4.16 kV grid to a 480 V grid or load. Simulation results and are provided to evaluate the protection schemes. Initial experimental test results are also provided.