Transient stability margin of variable versus fixed speed wind systems in electrical grids

For networks with large scale integration of wind farms this paper demonstrates a significant difference between the transient behavior of variable speed wind systems that adopt doubly fed induction generators with a four quadrant ac-to-ac converter connected to the rotor windings (DFIG) and a fixed speed wind system, where the conventional cage induction generator is used. The reason for this difference is explained, and it is shown that the phenomenon is due to the ability of the two dedicated rotor current regulators of the DFIG to control the electrical torque and reactive power quickly and accurately. This difference is clearly observed after a severe fault (short circuit) occurrence. It will be demonstrated that the adjustable speed generator (DFIG) enhances system stability in power networks.