Grid-Forming Cascaded-Bridge Converters With Parallel Connectivity

Grid-forming converters (GFMCs) offer a range of desirable features, such as grid formulation, inertia and damping emulation, voltage/frequency support, and better stability in weak grids. In parallel, cascaded-bridge converters (CBCs), such as cascaded H-bridge converters (CHBs), enjoy the advantages of modularity and expandability, thus being promising candidates in high-voltage GFMCs. Although the serial connection of submodules enables high-voltage stresses, CHB submodules fail to jointly share the current. Therefore, conventional CHBs can hardly comply with short-term overload requirements, which remain a tricky problem for GFMCs. By leveraging the parallel capacity of symmetrical half-bridge submodules, this article proposes grid-forming CBCs with parallel connectivity, which benefits from: 1) implementation of multilevel converter GFM functionality and customized grid-supportive services; 2) increased current capacity; 3) minimization of sensor usage and control complexity; and 4) GFM capability sustainment under submodule faults. Simulation and experimental results confirm the validity of the proposed converter and control schemes, leading to a 30.7%-64.8% improvement of current capacity while realizing grid-forming functions, such as virtual inertia and damping synthesis.