Coordinated Control of DFIG Based Wind Farms and SGs for Improving Transient Stability

This paper proposes a coordinated control of doubly fed induction generator (DFIG)-based wind farms' (WFs) post-fault active power and synchronous generators' (SGs) tripping with the aim of improving transient stability of both the first swing and multi swings. To achieve it, the impact mechanism of the WFs' post-fault active power and SGs' tripping on the stability margin of each swing is first presented by using extended equal area criterion (EEAC). Based on this, a principle of the coordinated control is put forward. The WFs' control period is designed as six stages, and the value of post-fault active power in each stage is suggested to improve the stability of the first five swings and maintain the post-fault steady state. To decrease the tripping amount of the SGs, the SGs are tripped only when WFs' control effect is not sufficient to avoid the instability. Then, by utilizing an “online pre-decision and real-time matching”scheme, an engineering application method for the control principle is proposed, where the control procedures and detailed parameters calculation are demonstrated. The numerical simulations show that the coordinated control has a better damping effect and a less control cost (less amount of tripped SGs) than the traditional DFIG control or traditional SG tripping.