Modal Analysis of a Grid Connected Doubly-Fed Induction Generator

This paper presents the modal analysis of a grid connected doubly-fed induction generator. The inherent oscillating modes of the DFIG are determined with the single machine infinite bus power system model. The effects of initial rotor speed and grid strength on the machine dynamics are studied. The conditions for which stator transients can be neglected are also determined. Nomenclature e´qs e´ds [pu] equivalent internal q- and d-axis voltage ??qr ??dr [pu] rotor q- and d-flux Lss Lrr Lm [pu] stator, rotor and mutual inductance Rs Rr [pu] stator and rotor resistance ??elB [rad/s] electrical base speed = 2??50 rad/s ??s ??r [pu] synchronous and rotor speed iqs ids iqr idr [pu] stator and rotor q- and d-current Vqs Vds Vqr Vdr [pU] stator and rotor q- and d-voltage Hg Ht [s] generator and turbine inertia ??tw [rad] shaft twist angle Tshaft Te [pu] shaft and electromagnetic torque Vb [pu] infinite bus voltage magnitude y [rad] angle betw. inf. bus and DFIG voltages