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

Abstract

Motivated by the emergence of power systems that consist of HVAC and HVDC subgrids this work focuses on gridforming (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.