  This work focuses on grid-forming (GFM) control of Interconnecting Power
Converters (IPCs) that are used to interconnect multiple HVAC and HVDC subgrids
to form a grid of grids. 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.
