State control of DFIG in converter-fixed reference frame for wind-energy plants with focus on parameter uncertainties

Doubly-fed induction generators (DFIG) still play an important role in wind-energy applications. One of the major challenges concerning their operation is to meet not only steadystate, but also dynamic requirements. State-of-the-art DFIGs are often controlled applying dq-control structures to guarantee steady-state power-quality requirements. The need of an exactly known transformation angle causes problems, especially under grid-faults. Flux-based approaches offer more potential under grid-faults but these approaches do not offer current control which is essential to fulfil certain requirements under grid conditions. A new control approach based on inverter-fixed coordinates is presented, allowing fast reaction to dynamics and satisfying also the steady-state power-quality requirements. The advantages of both, current control and inverter-fixed reference frame, are combined in this control concept. Even under model uncertainties, the new approach provides highly dynamic behaviour and good steady-state operation which is under analysis in this paper.