Revisiting the Effect of Grid-Following Converter on Frequency Dynamics - Part II: Spatial Difference

In addition to the center-of-inertia (COI) frequency dynamics discussed in Part I, spatial frequency difference in power systems with grid-following (GFL) converters is also of critical importance. Part II revisits the influence of GFLs on spatial frequency difference. Building on the interfacing state variables and equivalent frequency defined in Part I, this work proposes an extended frequency divider (FD) formula. A mapping between network node frequency and both the synchronous generator (SG) rotor frequency and GFL equivalent frequency is established. The superposition contribution of GFLs is shown to depend on the electrical distance between the GFL and the frequency observation node, as well as on system power flow conditions, without relying on assumptions about the system operating state. Furthermore, this work addresses the frequency mapping of branch currents for the first time. Simulation results confirm the accuracy of the proposed extended FD, quantitatively demonstrating that the contribution of GFLs to nodal frequency is relatively weak and that the superposition coefficients are timevarying. The branch current frequency superposition reveals a complex and distinctly different pattern.