Dynamic Performance Evaluation of Grid-Following and Grid-Forming Inverters for Frequency Support in Low Inertia Transmission Grids

Abstract

In transition to the renewable-rich power grid, the involving system will face the challenges of loss of inertia and control paradigm change due to the retiring of synchronous machines and the fast integrating of inverter-based resources (IBRs). A fundamental and emergent question that needs to be addressed is how to achieve adequate frequency regulation by IBRs in a low inertia power system. This paper presents and compares several possible IBR control methods to provide frequency support including grid following control with frequency-real power droop, droop-based grid forming control and virtual synchronous machine (VSM)-based grid forming control. With each method, the frequency dynamic performance and transient stability of a test system are evaluated. The rate of change of frequency (RoCoF), frequency nadir and critical clearing time are selected as metrics to compare the performance and stability of the different methods. Preliminary results from the case study indicate that while the grid following control with frequency-real power droop can achieve similar frequency nadir as the grid forming methods, its RoCoF tends to be higher and transient stability margin tends to be smaller.