Immittance Model Estimation of Grid-connected VSCs: A Dual-linear Dependence

Future power grids are expected to be supported by a large number of inverter-based resources (IBRs), but the physical implementation of these IBRs varies significantly and may be confidential. Therefore, the immittance model of IBRs is a key tool for stability analysis of power systems with high IBR penetrations. However, obtaining the immittance model of IBRs over a wide operating range remains challenging. In this paper, a new dual-linear dependence is discovered and proposed, specifically that the admittance model of Grid-Following (GFL) controlled VSCs and the impedance model of Grid-Forming (GFM) controlled VSCs exhibit a strong linear dependence on operating points. Based on this discovery, this paper proposes an immittance model estimation framework utilizing Takagi-Sugeno (T-S) fuzzy logic. This framework can interpolate or extrapolate the immittance models across the entire operating range using immittance measurement data from only eight operating points, effectively eliminating the need for a large amount of immittance measurements, avoiding the computational burden of neural network training, and possessing interpretability. This paper comprehensively evaluates and verifies the computational speed, effectiveness, and accuracy of the proposed framework from the perspectives of absolute error and eigenvalue error.