Hierarchical Failure Mode Effect Analysis for the Protection Design of a MV AC-DC Solid State Transformer based EV Extreme Fast Charging Station

Solid state transformer (SST) is one of the key technologies that enable efficient and high power density extreme fast charging (XFC) stations for electric vehicles (EV). To ensure the safe and reliable operation of the SST, a robust fault protection system is essential. In this paper, a hierarchical failure mode effect analysis (FMEA) is carried out to enable a systematic design of the internal fault protection system of a 1MVA multilevel medium voltage (MV) SST for the Extreme Fast Charger. First, the MV SST is divided into several subsystems based on its functionality and FMEA is conducted on the components to identify and simulate local fault scenarios. From the module level FMEA, a local protection system consisting of sensors, actuators, and the protection logic of the local controller (LCon) is developed. Subsequently, system level FMEA is conducted to develop the global protection system for the SST which is embedded in the central controller (CCon).