Robust Structural Load Mitigation Control for Wind Turbines in Low Wind Speed Region

Wind turbines growth in size and flexibility leads to increased structural loads. These loads affect the lifetime of the turbines and increase related maintenance cost. During the past decade, advanced control strategies have been developed and adopted effectively to mitigate structural loads. However, most of the attempts focus on the above-rated region, only a few research relate to loads reduction in low wind speed region, which is below-rated. The main problem of below-rated region wind turbine control is to reduce structural loads without affecting the maximum power production. Most of the load mitigation control methods rely on the linear model linearized at a designed operating point, so control performance may deteriorate when the turbine operates at varying wind speed. In this paper, an observer-based controller, which is robust to wind speed change, is used in combination with a baseline maximum power point tracking controller to mitigate structural loads while keeping the maximum power captured. Simulation results using a high fidelity wind turbine model show that the proposed approach can realize multi-objective power and load control, and robustly make a reasonable compromise between power production maximization and structural loads reduction despite continuously varying wind speed.