Disturbance Observer-Based Super-Twisting SMC for Variable Speed Wind Energy Conversion System Under Parametric Uncertainties

Effective control of the generator’s shaft speed will ensure maximum power is captured from the wind turbines. However, the parameters of the wind energy conversion system (WECS)-based generators, including stator resistance and inductance, could change over time due to power loss, winding degradation, or core saturation. These parametric uncertainties affect the performance of the designed controllers. Although the sliding mode controllers (SMCs) are robust to matched uncertainties, the unmatched parametric uncertainties were not effectively compensated for by the SMC. This study investigated the performance of the SMC and super-twisting SMC (ST-SMC) under unmatched uncertainties using variable wind speed. Initially, the controllers were designed with the nominal parameters of the WECS-based permanent magnet synchronous generator (PMSG). Then, the values of the stator resistance and inductance were changed without changing the control design to test the robustness of the controllers to unmatched uncertainties. Finally, the uncertainties were estimated by the disturbance observer and incorporated into the controllers as a compensation mechanism. The controllers were designed using the synthetic wind profile and validated with the real-wind data. The transient and overall response of the controllers were analyzed using mean-absolute error (MAE) and root-mean-square error (RMSE) of the shaft speed tracking. The results demonstrated that the uncertainty compensation-based SMC/ST-SMC approach provides satisfactory shaft speed tracking performance even under parametric uncertainties.