Dual-port grid-forming control of MMCs and its applications to grids of grids.

Motivated by the emergence of power systems that consist of HVAC and HVDC subgrids this work focuses on grid-forming (GFM) control of Interconnecting Power Converters (IPCs) that are the key elements for connecting HVAC and HVDC systems. We introduce the concept of dual-port GFM control that leverages the ability of Modular Multilevel Converters (MMCs) to simultaneously form its AC and DC terminal voltage and present two dual-port GFM MMC controls. We provide analytical results and high-fidelity simulations that demonstrate that (i) dual-port GFM control is more resilient to contingencies (i.e., line and generator outages) than state-of-the-art single-port GFM control, and (ii) unlike single-port GFM control, dual-port GFM control does not require assigning grid-forming and grid-following (GFL) roles to the IPC terminals in grids of grids. Finally, we provide an in-depth discussion and comparison of single-port GFM control and the proposed dual-port GFM controls.