Solid-State Transformers with Input-Series/Output-Parallel configuration offer a convenient solution for AC/DC power transformation, but are affected by a second-order harmonic ripple due to a local single-phase AC/DC conversion in each module. This ripple can be counteracted by installing active filters, eliminating the need for oversized DC-bus capacitances. However, in an ISOP SST, dynamic interactions may arise from the coupling between different modules. This paper analyzes their effect on the closed-loop stability. It is shown that achieving stability for an active filter individually is not sufficient to guarantee the stability when multiple units are operated at once, but stronger requirements are needed. The analysis is supported by experimental validation, and the results can aid to improve the robustness of future designs.
