Publications Details

Suppressing Post-Fault Active Power Transients in Grid-Forming Inverters

Elliott, Ryan T.; Darbali-Zamora, Rachid

With the advent of grid-forming inverters, the question of how they behave during and immediately following short-circuit faults has become of major importance in the choice of control strategy and inverter design. This problem has greatly stimulated activity in the study of power electronics and their effects on large-scale systems, as evidenced by the formation of the Universal Interoperability for Grid-Forming Inverters (UNIFI) Consortium. This paper investigates a particular droop-controlled grid-forming inverter model called REGFM-Al, recently ap-proved for use in system-wide studies by the WECC Modeling and Validation Subcommittee. We show that following 3-phase faults, inverters that behave according to the REGFM-Al specification may inject significant post-fault active power transients. We describe the mechanism by which this occurs and propose a state reset strategy for mitigating the amplitude of these transients. To illustrate the main concepts, we present simulation results for a two-area test system augmented with a 200MVA solar photovoltaic power plant represented as a single equivalent grid-forming inverter. The analysis described in this paper was performed in MATLAB using the Power and Energy Storage Systems Toolbox (PSTess). To validate the model implementation in PSTess, we compared simulation results against GE Vernova's Positive Sequence Load Flow (PSLF) software.