Control System Design for Doubly-Fed Induction Generator (DFIG) in Wind Turbine Applications

This thesis comprehensively investigates control system design, performance analysis, and grid synchronization methodologies for a wind turbine-driven Doubly-Fed Induction Generator (DFIG). The DFIG represents a specialized induction machine configuration featuring two back-to-back power converters. The grid-side converter interfaces the stator winding with the electrical grid, while the rotor-side converter connects to the machine's rotor circuit through a DC-link capacitor, with control algorithms typically implemented using Park transformations and PI regulators for decoupled power control.

The research provides detailed exposition of control system architecture developed using stator-voltage and stator-flux oriented reference frames. The implementation involves mathematical modeling of machine dynamics in dq-coordinates, simulation development using tools like MATLAB/Simulink with subsystems for converter control and grid synchronization, and experimental validation through prototype testing. The study further examines advanced grid synchronization techniques, particularly emphasizing phase-locked loop (PLL) algorithms for stator-voltage synchronization with grid parameters, including implementation details for frequency and phase detection circuits.

Additionally, the work analyzes DFIG applications in renewable energy systems, highlighting operational advantages in wind power generation including enhanced efficiency through optimal speed control, improved power quality via active/reactive power regulation, and increased reliability through fault-ride-through capability implementation. The thesis concludes by identifying future research directions involving advanced control algorithms like model predictive control and artificial intelligence-based synchronization techniques for enhanced grid stability.