Enhanced model of the doubly fed induction generator-based wind farm for small-signal stability studies of weak power system

This study proposes an enhanced model of the doubly fed induction generator (DFIG)-based wind farm (WF) for small-signal stability (SSS) studies of weak power system. This model consists of a wind turbine, a drive train, a simplified generator/converter module and associated controls. As analysed and verified in this study, the dynamics of the phase-locked-loop and the rotor current loop are important for accurate SSS studies of the weak power system involving the DFIG-based WF and thus should be modelled appropriately. The enhanced model is validated by eigenvalue analysis and time-domain simulations. Compared with the detailed model, the WT3 model provided by General electric (GE) energy and the conventional model, the enhanced model presents high precision and satisfactory simplification for SSS studies. As the application of the enhanced model, a case study is carried out to explore the impact of WF ancillary voltage/frequency controls on SSS of the weak grid. As indicated in this study, the WF ancillary controls exert distinct impact on SSS. New lightly damped power oscillations can be introduced. Therefore extra measures should be considered if the ancillary controls are required by the WF in order to satisfy the future grid codes.