DFIG Wind Turbine Novel Cascade Control guaranteeing Sensorless Field Orientation and Stability

The most common techniques employed for the control of doubly-fed induction generator (DFIG) wind turbine systems are restricted to either the well-known field-orientation control (FOC) or the direct-power control (DPC), with each one of them, however, suffering in one way or another from distinctive drawbacks. Instead of these standard methods, in this paper, a novel and nonlinear model-based control approach is adopted, which is developed in view of the entire system structure and characteristics. The key novelties introduced by the proposed design are due to an innovative technique, defined as 3s-FOC, which is formulated to enable the implementation of a simple cascade-mode PI-based control scheme that i) achieves stator field orientation without the need for estimating the actual flux, ii) guarantees system stability while simultaneously provide a relaxation on the transient response, iii) improves the closed-loop system dynamic behavior by employing extra damping terms in the inner-loop current regulators. The stability and state convergence properties of the complete system is firmly ensured as it is verified by a rigorous analysis based on advanced Lyapunov-based methods and input-to-state stability (ISS) techniques. Finally, a thorough simulation is conducted, which firmly verifies the theoretical results and the superior controlled system dynamic performance.