| Description |
Type-3 wind turbine generators, otherwise known as the Doubly-Fed Induction Generators (DFIG), have gained significant attention due to the smaller rating of their power electronic converter and decoupled control of active and reactive powers. This dissertation deals with the modeling, analysis, and design of feedback controllers for gridconnected DFIGs. Due to the unique structure of the DFIG's model, the analysis and design of the proposed control laws are simplified by transforming their representation into equivalent systems with complex coefficients and half the number of poles. The complex domain framework allows for the simplified design of controllers that can ensure stability and performance. Three rotor voltage control laws have been proposed for the direct connection of a DFIG-based wind farm to the grid. These control laws are of increasing levels of complexity and place the poles of the feedback system at desired locations in the left-half plane. All three controllers demonstrate acceptable dynamic responses depending on the choice of the closed-loop poles. In addition to simulations, the performance of the proposed controllers has been validated in experiments on a laboratory testbed. An advantage of the complex vector representation is that 2×2 feedback systems with real coefficients can be analyzed as single-input single-output (SISO) systems. This simplifies the robustness analysis and derivation of the system stability margins. |
