HT-PLL-Based Seamless Transition Strategy for DFIG With Power Quality Enhancement Through Fractional-Order Adaptive Filter

This article focuses on the seamless operational mode transition of a doubly-fed induction generator (DFIG) driven by a wind turbine (WT). Moreover, remote geographical allocation of wind farm installations demands power quality (PQ) improvement features, where the WT becomes a significant contributor to grid stability. This article presents a real-time implementation of a seamless transition of DFIG-based WT with the grid. The seamless transition process is aided by accurate phase angle estimates from a half-tangent phase-locked loop (PLL) technique, which is an improved version of synchronous reference frame (SRF) based PLL. The phase detector of SRF-PLL is aided with HT function, which improves the accuracy at steady state and has faster dynamics under large frequency excursions. For PQ enhancement, an adaptive filter-based current control approach is suggested for grid-side converter during grid-feeding operation. The adaptive filter is based on a fractional-order gradient-descent total least mean p-norm algorithm. The benefit of this algorithm compared to its parent total least square methods is its ability to repress impulse noises in the eccentricities of the signal, showing a better convergence rate. The proposed control approaches are tested and compared with popular methods in simulation, and an experimental setup validates the satisfactory operation by subjecting through dynamic conditions and load unbalances.