Dynamic Fault-Tolerant Control of Dual-Purpose Grid-Forming Inverters for Harmonic Mitigation and Energy Storage

The growing penetration of renewable energy sources demands advanced control technologies to maintain grid stability and reliability, and grid-forming inverters (GFMs) have emerged as a promising solution to address this challenge. This paper presents a novel approach for managing power quality and energy storage in grid-connected systems through dual-purpose GFMs. In the proposed framework, one GFM connects a photovoltaic (PV) solar farm to the grid, while another GFM provides energy storage support and harmonic mitigation. The second GFM, referred to as the storage-GFM inverter, addresses challenges introduced by active loads, such as electric arc furnaces and pulse radars, which produce discontinuous high-magnitude harmonics. When the total harmonic distortion (THD) of the load current exceeds the predefined value, the storage GFM inverter switches to Shunt Active Filter (SAF) mode, ensuring compliance with IEEE 519-2022 harmonic limits. In the absence of active load, the storage GFM inverter functions as an inverter for the storage system, charging or discharging based on system demand. Both inverters operate in grid-following mode under normal grid conditions and can seamlessly transition to grid-forming mode during grid outages to maintain an islanded system. A key novelty of this work is the integration of a single inverter topology capable of performing multiple roles, including grid forming, harmonic filtering, and fault current limitation. The versatility of these inverters provides both stability through grid-forming capabilities and safety through effective harmonic elimination and fault current limitation.