Comparison of Two Fractional-Order High-Order SMC Techniques for DFIG-Based Wind Turbines: Theory and Simulation Results

Abstract

Two new nonlinear techniques are proposed in this study for improving the performance and efficiency of the doubly-fed induction generator (DFIG)-based wind turbine systems. Direct torque control (DTC) is among the most widely used strategies for controlling DFIGs due to its many advantages, such as robustness, simplicity, and fast response dynamics. However, this control causes big ripples in both torque and flux. Furthermore, it has significant total harmonic distortion (THD). Several solutions are proposed to overcome these problems, including nonlinear techniques and intelligent strategies such as genetic algorithms. In this work, two different controllers are proposed to improve the performance of the DTC technique. Firstly, the second-order continuous sliding mode (SOCSM) based on fractional-order (FO) control, and secondly, the super twisting algorithm (STA) based on the FO technique. The biggest advantages of the proposed strategies are their durability and ease of execution. Based on the proposed controls, the DTC strategy can greatly improve generator performance in different operating conditions. This paper also provides a comparative analysis of DTC-FOSOCSMC, DTC, and DTC-FOSTA in terms of reference tracking, robustness, chattering reduction, and computational complexity, using mathematical theory and simulation carried out in Matlab/Simulink using a 1.5 MW DFIG-based wind turbine. The simulation results demonstrate the effectiveness and high performance of the proposed DTC techniques.