Prognostics-based adaptive control strategy for lifetime control of wind turbines

Abstract

Abstract. Variability of wind profiles in both space and time is responsible for fatigue loading in wind turbine components. Advanced control methods for mitigating structural loading in these components have been proposed in previous works. These also incorporate other objectives like speed and power regulation for above-rated wind speed operation. In recent years, lifetime control and extension strategies have been proposed to guaranty power supply and operational reliability of wind turbines. These control strategies typically rely on a fatigue load evaluation criteria to determine the consumed lifetime of these components, subsequently varying the control set-point to guaranty a desired lifetime of the components. Most of these methods focus on controlling the lifetime of specific structural components of a wind turbine, typically the rotor blade or tower. Additionally, controllers are often designed to be valid about specific operating points, hence exhibit deteriorating performance in varying operating conditions. Therefore, they are not able to guaranty a desired lifetime in varying wind conditions. In this paper an adaptive lifetime control strategy is proposed for controlled ageing of rotor blades to guaranty a desired lifetime, while considering damage accumulation level in the tower. The method relies on an online structural health monitoring system to vary the lifetime controller gains based on a State of Health (SoH) measure by considering the desired lifetime at every time-step. For demonstration, a 1.5 MW National Renewable Energy Laboratory (NREL) reference wind turbine is used. The proposed adaptive lifetime controller regulates structural loading in the rotor blades to guaranty a predefined damage level at the desired lifetime without sacrificing on the speed regulation performance of the wind turbine. Additionally, significant reduction in the tower fatigue damage is observed.

Observer-Based Disturbance Accommodation Control Strategy for Useful Lifetime Control and Structural Load Mitigation of Wind Turbines

“…The lifetime control reduces the flapwise bending moments with a standard deviation of 72.6%. Similar observations are also supported by the results achieved in [17] [18] and [19] [26].…”

“…The lifetime control strategy reduces the tower fore-aft moments with a standard deviation of 4.4% in Figure 10(b). These results are supported by studies in [17] [19] which show that tower fore-aft moments are influenced by the blade load mitigation.…”

“…Therefore, showing that the lifetime control strategy delays degradation hence ensuring the blades do not fail before the expected lifetime. Various studies in [17] [18] and [19] [26] also support that reducing structural loads in blades reduces damage accumulation.…”

“…This indicates that the control strategy in this paper is able to efficiently mitigate structural loads without compromising the generator power performance. Structural load mitigation and power regulation are also achieved in [17] and [19] but a slight compromise on power generation was noted in [19].…”

“…If the wind turbine component's operational lifetime according to the manufacturer is given, then the Remaining Useful Lifetime (RUL) of the component as in [17] can be calculated as…”