A Novel Multilevel Solid-State Transformer for Hybrid Power Grids

This paper presents a new proposed topology of a solid-state transformer (SST) for application in hybrid power grids (ac and dc), in which the possibility of operating with various voltage levels (multilevel) in both sides is the main characteristic. At the interface with the power grid (primary side), the proposed SST consists of an ac-dc converter in Y configuration that guarantees operation with five levels in each phase-to-neutral voltage. To establish the hybrid power grid on the secondary side, the SST is composed of a dc-ac converter in Y configuration to establish an ac-grid, also operating with five levels in each phase-to-neutral voltage, and by a dc-dc converter to establish a dc-grid, which operates with three voltage levels. The interface between the converters of the primary side and the secondary side is guaranteed by an intermediary isolated dc-dc converter. As fundamental requirements, the proposed SST operates with balanced and sinusoidal currents on the primary side, and with balanced and sinusoidal voltages on the secondary side (ac-grid), as well as controlled voltages and currents on the dc-grid. Throughout the paper, the proposed topology for the SST is described in detail, with the operating principle of each converter being presented. The obtained results, both on steady-state and transient-state, for several main operating conditions, prove the correct functioning of the proposed SST, highlighting important features that contextualize the operation of the proposed SST in smart grids.