Investigations on Service Extensions of Solid State Transformer

Abstract

Solid State Transformers (SSTs) are receiving significant research attention in recent years as the countries around the world gear up for low carbon future. Though SSTs are contemplated as a prospective replacement to line frequency transformers (LFTs), they are far more superior to the latter in extending their services besides isolation and voltage conversion. They are multifunctional with all power quality conditioning functions embodied in a single entity. This paper investigates the possible service additions that could be offered by the SSTs deployed in power distribution systems. The additional services include harmonic reduction, mitigation of sag/swell/load transients, compensation for outage, power factor correction, voltage regulation under unbalanced loads, capacity addition to LFTs and provision of low and medium voltage dc output. The investigations are carried out by modeling a three-stage SST with two-switch bridgeless boost power factor correction (BBPFC) converter for the front end, Dual Half-bridge (DHB) converter for the isolation stage followed by a full bridge SPWM inverter for the final stage. The choice of converter topologies for the three stages of the SST is justified on the basis of active part count, control performance and operational simplicity. Further, the modeled SST is modular providing room for extended power and voltage levels, fault isolation and easy maintenance. Simulation results are presented in support of the investigations.