A ISOP AC-AC Hybrid Switched-Capacitor SRC for Solid State Transformer Applications

This paper presents the one phase of a three-phase solid-state transformer (SST), which will be employed in a 13.8 kV / 220 V distribution system, realized as input-series output-parallel (ISOP) arrangement of multiple AC-|AC| modules and by a |AC|-AC unfolding stage. The modules are compounded by a front-end AC-|AC| active rectifier and by a |AC|-|AC| hybrid switched-capacitor series resonant converter (HSCSRC). The auto-balancing among the modules, the absence of large DC link capacitors and the simple modulation scheme are some advantages of the proposed SST. Experimental results are presented for a laboratory prototype of an ISOP arrangement of two modules with the unfolding stage for theoretical validation. The system rated power is 3.4 kVA with 2.3 kV input voltage and 220 V output voltage. The prototype holds a maximum efficiency of 96.8%.