Mixed-Sensitivity Robust Disturbance Accommodating Control for Load Mitigation and Speed Regulation of Wind Turbines

To meet ever-growing global demand of renewable energy, wind turbines have seen an exponential growth in size over the past few decades to capture more energy from wind. This has led to a growing concern of increased loading of wind turbine components as a result of additional weight and flexibility, hence, affecting operational and power reliability. To tackle this challenge, this contribution proposes a robust observer-based control strategy for mitigating structural loads as well as regulating power production of utility-scale wind turbines. Variation of the rotor effective wind profile, which is responsible for fatigue loading of turbine components, acts as a disturbance to the wind energy conversion system. Additionally, linear models used to design most wind turbine control systems have inherent modeling errors and do not capture nonlinearities caused by changing operating conditions. Although robust controllers address this challenge, they do not incorporate wind disturbance models. A few robust disturbance accommodating controllers have been proposed before to mitigate modeling errors and nonlinearities due to wind disturbances. However, these have been tested on smaller wind turbines. Their performance have also not been benchmarked against the latest baseline controllers. Therefore, this contribution proposes to extend this control strategy to an onshore 5 MW National Renewable Energy Laboratory (NREL) reference wind turbine (RWT) and compares its performance against the recently developed proportional-integral (PI)-based baseline controller from NREL, the reference open-source controller (ROSCO). Based on simulations results for various wind profiles, the proposed control scheme improves tower load mitigation and generator speed regulation performance.