Evaluation of Closed-loop Control Techniques for Single-stage MVAC-LVDC Solid-State-Transformers in Compact EV Ultra-Fast Charging Stations

Though power-dense and efficient single-stage Solid-state-transformer (SST) based futuristic electric-vehicle (EV) ultra-fast charging station (EV-UFCS) solutions are proposed, their underlying control techniques are not comprehensively analysed in prevalent literature. In this paper, three available control techniques presented in literature, viz. (i) standalone low-voltage DC (LVDC) bus Voltage Control, (ii) LVDC bus Voltage Control augmented with conventional Power Balance Control (PBC) and (iii) recently proposed Multi-objective Optimal Control (MOC), are investigated for the single-stage SST-based grid-interface of an EV-UFCS. Experimental comparison is presented while using measurements taken during implementation of the three investigated control techniques in a single-stage SST experimental setup operated at 11.7 kVA(pk) load. This comparative analysis clearly shows that the Multi-objective Optimal Control strategy results in a higher efficiency (especially at lower loads) while restricting grid-side current THD within given grid-code limits, and thus proves to be a superior control choice.