Steady state modeling and analysis of DFIG for variable-speed variable-pitch wind turbines

Due to its advantages, doubly-fed induction generator (DFIG) based variable-speed wind turbines (VSWT) are recently the most widely used topology of wind energy conversion systems (WECS). This paper provides a steady-state modeling and analysis of DFIG systems. A steady-state model for DFIG is derived based on a wound-rotor induction machine 3rd order model with a stator flux-oriented control scheme. This model is used for steady-state performance analysis of DFIG system connected directly to an infinite bus considering the optimal operation through following of the maximum power tracking characteristics. A fundamental steady-state stability criterion based on DFIG power-slip characteristics is used to study the steady-state stability of the system considering the entire maximum power-tracking characteristics. Also, the solo effect of the rotor voltage d-q components on the doubly fed induction machine (DFIM) steady-state performance and stability is analyzed. The results illustrate the steady-state stability limitations, as well as causes of steady-state instabilities of DFIG system as affected by the stator power demanded and the rotor-impressed variables. Moreover, DFIG rotor-speed range limitation causes and indicators that hinder steady-state stability are assessed. Therefore, the presented work is valuable for steady-state operation management of DFIG systems. Future work may include experimental verification of the given results and finding ways for improving stability of DFIG.