Frequency-Domain Injection-Based Equivalent Impedance Identification for Distribution Networks with High-Penetration Distributed PV

The rapid proliferation of distributed photovoltaic (PV) systems under the carbon peaking and carbon neutrality goals has fundamentally altered the structure and operational characteristics of distribution networks. The transition from a single-source radial network to a multi-source interactive active network introduces significant variations in system equivalent impedance, complicating protection coordination and degrading relay performance. Existing impedance identification methods, whether offline simulation-based or online measurement-based, suffer from inherent limitations: offline approaches rely on imprecisely obtainable network parameters, while online techniques such as the least-squares and statistical relationship methods are vulnerable to parameter drift, leading to considerable estimation errors. To overcome these challenges, this paper proposes a frequency-domain injection-based impedance identification approach. By superimposing harmonic voltage or current signals onto the inverter control references and extracting the steady-state response at specific frequencies using continuous wavelet transform with a Blackman window, the method achieves accurate equivalent impedance estimation. An abnormal data elimination procedure further enhances robustness against measurement noise. Hardware-in-the-loop simulations validate the proposed method under various PV capacities and complex frequency conditions. Results demonstrate that the proposed technique consistently maintains average identification errors below 5%, significantly outperforming conventional time-domain methods. The proposed method provides a reliable equivalent impedance identification approach and is of significant application value for protection coordination and relay performance enhancement in distribution networks with high-penetration, distributed PV.