Frequency-domain modelling and stability analysis of a DFIG-based wind energy conversion system under non-compensated AC grids: impedance modelling effects and consequences on stability

Impedance-based frequency-domain method is an effective tool for the stability assessment of a doubly fed induction generator (DFIG) system. Several impedance models have been proposed recently; however, these models are usually associated with model reductions since the complexity in achieving a detailed DFIG model. This may lead to unreliable stability results under certain conditions, and a clarification of this modelling effect is lacking in the literature. Therefore, this study aims to address this issue by developing a detailed DFIG impedance model. To achieve this target, a modular modelling technique is proposed instead of the conventional linearisation by parts, for which the components of a DFIG system are modelled as multi-port modules. Through this method, the detailed DFIG model together with four types of reduced-order models can be derived efficiently. The detailed DFIG model is verified by the measured frequency responses in PSCAD/EMTDC, along with its correctness in Nyquist-based stability analysis. Subsequently, four types of the reduced-order models are compared with the detailed one in terms of Nyquist plots, so that their performance and effectiveness for stability analysis are clarified. Besides, conclusions regarding the reduced-order models are also verified by time-domain simulations.