Comprehensive Impedance Analysis of DFIG-Based Wind Farms Considering Dynamic Couplings
Jinlong Wang, Peng Wang, Haoran Zhao, Futao Yang
Abstract
Existing wind farm impedance analyzes using aggregated impedance models neglect the influence mechanisms of dynamic couplings between wind farm control (WFC), wind turbines, and collector lines on system stability. This article proposes a novel comprehensive impedance model (CIM) for the wind farm based on the doubly-fed induction generator (DFIG), considering multiple dynamic couplings for thorough impedance analysis. At the DFIG level, small-signal characteristics of rotor speed are introduced into the impedance model to reflect couplings between mechanical and electromagnetic dynamics. Meanwhile, at the wind farm level, couplings between the WFC and DFIGs are represented as a current source controlled by voltage and current perturbations at the wind farm point of common coupling (PCC), connected in parallel with the original DFIG impedance. Since the PCC voltage and current are associated with all DFIGs and collector lines, this controlled source effectively captures their couplings. Analysis with CIM reveals that considering mechanical dynamics improves the accuracy of DFIG impedance in the low-frequency band, while the WFC affects the impedance characteristics of the wind farm in the full-frequency range. Moreover, excessively large WFC proportional-integral parameters can lead to system destabilization. Simulation and experimental results confirm the validity of the CIM and its precise application in stability analysis.