Modelling and real-time simulation of a modular bidirectional solid-state transformer for ultra-fast charging of electric vehicles

Abstract

This thesis proposes a modular Solid-State Transformer (SST) system architecture to be directly interfacing with a three-phase MV utility network enabling high-power and ultra-fast charging capabilities for electric vehicles, with the capacity to incorporate energy storage systems at the MVDC-link. This topological configuration allows bi-directional power flow for Vehicle-to-Grid and for scalability to higher voltage and power levels. A detailed model-based design of a multi-module SST is presented with 3.3 kV SiC MOSFETs for highly efficient charging rated at 1.5 MW, supplied by a 27.6 kV distribution feeder. The SST switching model is based on a high-frequency two-stage power conversion solution with a Cascaded H-Bridge (CHB) rectification stage followed by a Dual Active Bridge (DAB) conversion stage. Control strategies and modulation schemes are implemented to achieve voltage balance and unity power factor, and to mitigate current harmonics and voltage ripples in compliance with IEEE standards, validated by Model-in-the-Loop real-time simulation.