Optimized double-stage fractional order controllers for DFIG-based wind energy systems: A comparative study

This paper presents a nonlinear robust control approach based on a Fractional-Order Proportional-Integral-Derivative–Fractional-Order Proportional-Integral (FOPID-FOPI) controller, applied to the direct power control of a Doubly Fed Induction Generator (DFIG) in Wind Energy Conversion Systems (WECS). To achieve the desired control objectives, two dual-stage FOPID-FOPI controllers were implemented, resulting in a total of sixteen tunable parameters. Given the complexity of tuning these parameters, metaheuristic optimization techniques, specifically the Remora Optimization Algorithm (ROA) and Grey Wolf Optimization (GWO), were employed to optimize the controller gains by minimizing various cost functions, including the Integral of Time-multiplied Square Error (ITSE), Integral of Square Time-multiplied Square Error (ISTSE), Integral Square Time-multiplied Square Error (ISTES), and Integral Time Absolute Error (ITAE). Key criteria, such as response time and ripple of the stator power in the DFIG, were analyzed to evaluate performance. The results demonstrate that the ITAE-based ROA-FOPID-FOPI controller achieves the shortest response time of 0.23 ms for reactive power, 0.1 (ms) for active power, and a significant reduction in power ripple—75 % for active power and 66.66 % for reactive power. Additionally, the ITAE-based ROA-FOPID-FOPI controller reduces the Total Harmonic Distortion (THD) by 17.07 % compared to the GWO-optimized controller across all cost functions.Overall, the findings highlight the superior performance of the ITAE-based ROA-FOPID-FOPI controller in enhancing power quality and dynamic response in DFIG-based WECS.