Modeling, Analysis, and Design for Small-Signal Stability in Sequence-Decomposed Grid-Forming Control

Fast and accurate detection of symmetrical components is critical for ride-through of asymmetrical faults in grid-forming (GFM) inverter based resources (IBRs). Sequence-decomposed GFM control enables to emulate the behavior of a synchronous machine by an IBR in both positive- and negative-sequences, where current references are generated separately in each sequence from the extracted symmetrical components of the terminal voltage. Cross-coupled dynamics between the stationary frame components attributed by the symmetrical component extraction (SCE) complicates the analysis and design process and appropriate modeling and analysis method for sequence-decomposed GFM control structures is yet to be reported. In this work, a small-signal model is developed for the analysis and design of such control implementations. It is demonstrated that by virtue of its overall structure, sequence-decomposed GFM control enables simplified analysis eliminating the cross-coupled dynamics characteristic to SCE. Subsequently, comparative analysis is presented between delay based and filter based SCE methods focusing on their impact on small-signal stability. Design guidelines are provided along with supporting experimental evidence using a laboratory inverter prototype. The analysis and experiments demonstrate that delay based sequence component extraction method offers greater stability margins under open-load and loaded GFM operations.