Energization and Start-up of Modular Three-stage Solid State Transformers

Abstract

Grid-connection and startup of solid state transformers (SST) based on modular topologies are studied in this work. A simple solution is implemented to feed the auxiliary electronics (i.e. sensors, control boards, drivers, etc.) of each SST module. It is based on feeding this circuitry from the DC links of the module using Auxiliary Power Supplies (APS). However, this structure leads to a problematic energization of the SST due to the threshold input voltage of the APS. Before the DC link capacitors are charged to this voltage threshold, the APSs are not functional and consequently SST energization and connection to the grid are performed without monitoring. Although startup in this situation is problematic, adequate procedure can prevent unwanted transients. In this paper, a step-by-step simple procedure is proposed for energizing a three-stage SST based on a Cascaded H-Bridge (CHB) modular topology. Simulation results as well as experimental tests are presented.