Multi-Level Power Converter Using Series-Connected Solid-State Transformers

Solid state transformers (SSTs) and multi-level power conversion systems have been researched actively. These techniques are able to control voltage and current easier than conventional systems and have a potential to reduce the volume and weight of the power conversion systems. We develop a multilevel converter with the series-connected SST units for solar power conditioning system (PCS). In each SST unit, an LLC converter driven by SiC-MOSFETs are included, and we propose a control method of the LLC converter to keep the efficiency for solar PCS in which the input voltage form photovoltaic panel changes. The proposed method is evaluated with a prototype SST unit, and its efficiency shows 98% or more even if the case of the input voltage from the panel is relatively high.