This paper presents a novel transformerless interconnected cascade multilevel topology to improve the support of low- and medium-voltage distribution grids under unbalanced nonlinear loads. The proposed Interconnected Single-Star Bridge-Cells (iSSBC) is derived from the Single-Star Bridge-Cells (SSBC) and features the inclusion of three star-connected inductors, allowing the exchange of active power between the clusters. Therefore, the proposed topology can supply negative-sequence components to mitigate load disturbances at the grid-end current, enhancing the regulation capability in comparison to the SSBC. The power flux of the proposed topology is presented along with the control system. Experimental results validate the proposed topology combined to the proposed control system for grid current and dc voltage regulation under unbalanced nonlinear loads.