Comparative Study of Frequency Support Functions of IBRs for Bulk Power System Frequency Stability

Various grid support functions for inverter-based resources (IBRs) have been proposed to improve system stability. Impact analysis of the introduction of IBRs with grid support functions predominantly uses a small-scale or bulk system model, including only a few IBRs due to the computational burden. This paper compares the frequency support function of IBR for frequency stability of a bulk power system interconnected with subsystems including large numbers of IBRs using the reduced-order model method for a distribution system including IBRs. This paper examines the contribution to frequency stability of three types of IBRs: Grid-following inverters with Frequency-Watt function, droop-controlled grid-forming (GFM) inverters and virtual synchronous generator-based GFM inverters. Findings show that the Rate of Change of Frequency (RoCoF) was influenced by the contribution of the frequency support function of IBRs, as well as by the interrelationship between the load-voltage characteristic and the voltage support function of IBRs. The analysis is validated using time-domain simulations in the PSCAD/EMTDC environment.