Phaser-Based Transfer Function Analysis of Power Synchronization Control Instability for a Grid Forming Inverter in a Stiff Grid

The grid forming inverter (GFM) is considered a key technology to solve the issues of inverter-based resource (IBR)-rich grids. Many studies have investigated how GFM affects and improves power system stability. However, few studies have considered the instability of GFM as it relates to various grid conditions. This paper discusses the mechanism of power synchronization control instability of GFM by conducting transfer function analysis with focus on various grid conditions, the control logic of GFM, and relevant parameter setting. Based on the above analysis, a procedure for power synchronization controller design of GFM is proposed. Experimental tests in the control hardware in the loop (CHIL) environment are performed to verify the validity of the transfer function analysis and reveal that the instability of GFM is likely to occur when it is connected to stiff grids or experiences a larger phase delay due to a longer power measurement delay and lower damping of the controller.