Forward Dual-Active-Bridge Solid-State Transformer for a SiC-Based Cascaded Multilevel Converter Cell in Solar Applications

Central inverters based on conventional topologies are the current preferred solution in solar farms because of their low cost and simplicity. However, such topologies have some disadvantages such as poor maximum power tracking, use of bulky filters, and low-frequency transformers. An interesting alternative in this case is the SiC-based cascaded multilevel converter (CMC), which provides a distributed maximum power point tracking control with reduced footprint and high flexibility. Each cell of a CMC usually has, as an intermediate stage, a solid-state transformer based on a dual-active-bridge dc-dc converter. Due to the unidirectional power flow characteristic of the photovoltaic application and aiming at further reduction in the converter volume, this work proposes a forward dual-active-bridge (F-DAB) topology, which reduces the number of active switches. This paper shows through analytical, simulation, and experimental results that the cell using an F-DAB is superior to other unidirectional topologies in three aspects: higher power density with commercially available power modules, reduced part count, and simplicity of control.