Comparison of Grid-Following and Grid-Forming Inverters Performance for Frequency Stability in Power Systems: A Dynamic Study

The significant growth of the share of inverterbased resources in transmission power grids has led to changes in the dynamic nature of the power network. One of these changes is the significant reduction of network inertia and its direct impact on the frequency stability of the network. Therefore, it is necessary to provide appropriate control systems for inverter-based resources to maintain frequency stability. Accordingly, this article aims to compare and study the performance of several controllers based on the concepts of, 1) grid following inverters, such as decoupled-PQ and WECC. 2) grid-forming inverters, such as Synchronverter, droop, and virtual synchronous machine. To compare the performance of these control methods, frequency stability indicators such as rate of change of frequency and Nadir frequency have been used. Also, the constraints of the protection system (frequency relays) have been considered to assess the performance of these controllers in the primary frequency control loop. The results of dynamic simulations performed in the IEEE 39-Bus test system show, based on the nadir frequency index and the limitations of the protection system in the primary control loop, that the grid-forming controllers have performed better than the grid-following controllers.