Power system modal analysis considering doubly-fed induction generators

This paper presents a modal analysis of a two machine power system that includes a doubly-fed induction generator (DFIG). The DFIG's model considers rotor flux linkages as dynamic states and stator flux linkages as algebraic variables. Active- and reactive-power controllers are also modeled. Active power is tracked for optimal power extraction from the wind. Using the power system set of differential-algebraic equations, eigenvalue trajectories are obtained when the load is varied. The system dynamics show little interaction between the DFIG and the synchronous machine (base case). Thus, system behavior is compared when the DFIG is replaced by (i) a hypothetical synchronous generator and (ii) a negative load (NL). Results show that an NL model resembles very well a DFIG dynamic model in the power system. A high sensitivity with respect to the parameters of the fast loop of the power controllers is observed. Lowering the parameters of the reactive power controller can actually make the system more stable. With respect to the loading at the Hopf point, its estimation is obtained with a low error by the NL model. These results have been verified using a 39-bus, 10-machine system. Using an NL model for representing wind power generators in power systems analysis can provide reasonable results while reducing simulation time and model complexity.