Abstract
In recent years, doubly-fed induction generators (DFIGs) has become one of the major type of variable-speed fixed-frequency generators for large-scale wind farm applications. Some elementary sensor-based flux-oriented control strategies have been successfully implemented in current wind power industry practice. Similar to technology developments in conventional fixed-speed induction generator, sensorless control may be a new issue to further reduce sensor cost and provide similar satisfactory transient performance of sensor-based control. The main theme of this thesis is to study sensorless control algorithms for DFIGs. Both grid-connected and stand-alone configurations will be addressed. The main contributions of this thesis can be summarized as follows: Static characteristics of DFIGs and their operating capacity will be conducted first. Dynamical models in terms of both the voltage and current model on stator flux oriented control will be developed in the generalized flux-oriented scheme. And a laboratory real-time control 2.2 kW DFIG platform is developed. The system is constructed by Matlab/Simulink and xPC system. Finally two types of sensorless control, including the model reference adaptive system (MRAS) control and the full-order observer control, are studied. Detailed analysis are provided. Both software simulations and hardware experiments are conducted. Experimental works have been conducted to verify the effectiveness of the proposed control strategy. Comparion studies of both sensorless control laws are also discussed.