Coordinated strategy between positive- and negative-sequence currents of wind farms for transient stability enhancement of synchronous generators under asymmetrical grid faults

As the penetration of wind power is growing, it is demanded that wind farms should contribute to maintaining power system stability, for particularly under various grid fault conditions. Highly-penetrated wind farms are able to influence synchronous generators´ (SGs´) behaviour for transient stability enhancing by injecting the designed positive- and negative-sequence currents, especially when the electric distance between wind farms and SGs is short. In this paper, SG´s transient stability during asymmetrical grid faults is the centre of interest. The relationships between SG´s rotor swing function and wind turbines injecting currents are analysed based on the mathematical models of unbalanced power system. Coordinated requirements for positive- and negative-currents injection of wind turbines, for the purposes of to enhance transient stability, are proposed during asymmetrical faults. Time domain simulation validates the result.