Forward dual-active-bridge solid state transformer for a SiC-based cascated 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 as poor maximum power tracking, use of bulky filters and low frequency transformers. A good alternative in this case is the SiC-based Cascaded Multilevel Converter (CMC), which provides a distributed MPPT 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 (DAB) DC-DC Converter. Due to the unidirectional power flow characteristic of the photovoltaic application and aiming further reduction in the converter footprint, 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 two aspects: greater power density with the available power modules and simplicity of control.