Novel Autonomous Control of Grid-Forming DGs to Realize 100% Renewable Energy Grids

The grid-forming distributed generators (GFM-DGs) have attracted much attention as a key technology for realizing 100% renewable energy grids. This paper presents a novel control strategy to ensure the reliable operation of a renewable energy source (RES)-based GFM-DG even during weather variations. The GFM-DG connects a RES to the grid via source- and grid-side converters, with the converters' common DC-link voltage $V_{DC}$ indicating the power balance between the RES and the grid. We begin by identifying the limitation of conventional strategies in maintaining $V_{DC}$ against severe weather. To address the limitation, we propose a coordinated strategy for both source- and grid-side converters to regulate $V_{DC}$ cooperatively, ensuring GFM-DG stability even in adverse weather conditions while also achieving decentralized power sharing and contributions to frequency inertia and damping. The proposed strategy is applicable to photovoltaic- and wind turbine-based generators, as well as energy storage systems. A guideline for control parameter design and stability margin analysis for weather conditions are also provided. The effectiveness of the proposed strategy is validated via small-signal analysis and simulation case studies under various conditions of 100% renewable energy grids, characterized by severe weather, load demand changes, actual line impedances, and a grid fault.