Design, Analysis and Implementation of a 500kVA Hybrid Solid State Transformer

The Hybrid Solid State Transformer (HSST) is an amalgam of a resilient yet cost effective line frequency transformer (LFT) and a fractional power rated, controllable and responsive solid-state transformer (SST). Existing works have mainly focused on Hybrid Transformers (HT) where the required isolation is provided by an auxiliary line frequency winding or transformer making the distinction between HTs and FACTs devices less evident. This article proposes and studies an HSST system through a case-study of a 20kV/500kVA Hybrid Solid State Transformer (HSST) utilizing a single stage Dual Active Bridge (DAB) based SST complemented by simulation analysis, describing the plethora of control possibilities that undoubtedly improve the operational flexibility in the grid. A hardware prototype of the 20kV HSST unit has been assembled and tested, demonstrating some of the control functionalities, and demonstrating efficiencies of up to 98.4%.