Comparison of stabilizing methods for doubly-fed induction generators for wind turbines

In this paper the stability of doubly-fed induction generators (DFIG) is investigated. At present, as countermeasure in case of fault near or far from the generator, the most common action to limit the negative effects on the generator stability and to preserve the power electronic equipment is to disconnect the back-to-back converter and short circuit the machine rotor with a crowbar. Main disadvantage of such strategy is that it is not possible to increase the stability area of the machine. As a consequence, frequently the generator goes unstable. In this paper a new stabilizing method for the DFIG is proposed. Furthermore, it is shown how this method protects the power electronic equipment of the DFIG and considerably increases the stability area during faults in comparison with the application of crowbar. The paper presents the simulation of a single DFIG connected to a high voltage system and of a DFIG wind park connected to a bus of a local energy system (LES). The LES is modelled as a meshed medium voltage islanding network with synchronous generators, lumped loads and local generation units as well. Numerical results under ATP-EMTP assuming disturbances of short duration are reported