Ultrafast Grid Impedance Identification In Dq-Asymmetric Three-Phase Power Systems

The identification of dq-asymmetric impedances presents a challenging estimation problem due to the strong crosscoupling between axes, which is especially prominent at low frequencies. Conventional identification schemes are often hampered by the requirement for sequential perturbations or the difficulty of selecting appropriate global parametric models. This paper introduces an active non-parametric frequency-domain approach that utilizes complex transfer functions and local parametric approximations. This formulation eliminates the requirement for periodic steady-state measurements while providing precision comparable to that of correctly specified parametric models. By solving localized linear least-squares problems, the approach maintains high computational efficiency while remaining agnostic to the specific grid structure. Electromagnetic transient (EMT) simulations demonstrate that the proposed method achieves highfidelity identification with a 1 Hz frequency resolution using only one second of noise-corrupted measurements. The results confirm a significant reduction in measurement time compared to available techniques. Additionally, the approach shows superior robustness against model-order selection errors, ensuring accurate wideband modelling of grid dynamics.