Reduction of Structural Loads in Wind Turbines Based on an Adapted Control Strategy Concerning Online Fatigue Damage Evaluation Models

Abstract

In recent years, the rapidly-increasing demand for energy generation from renewable resources has been noticeable. Additional requirements are consequently set on Wind Turbine (WT) systems, primarily reflected in WT size and power rating increases. With the size increase of WT, structural loads/fatigue stress on the wind turbine become larger, simultaneously leading to its accelerated aging and the shortening of its lifetime. The primary goal of this contribution is to establish an approach for structural load reduction while retaining or slightly sacrificing the power production requirements. The approach/control strategy includes knowledge about current fatigue damage and/or damage increments and consists of multi-input multi-output controllers with variable control parameters. By the appropriate selection of the designed Multi-Input Multi-Output (MIMO) controllers, the mitigation of structural loads in accordance with a predefined range of accumulated fatigue damage or damage increments, exactly to the extent required to provide a predefined service lifetime, is obtained. The validation of the aforementioned control strategy is based on the simulation results and the WT model developed by National Renewable Energy Laboratory (NREL). The obtained results prove the efficiency of the proposed control strategy with respect to the reduction of rotor blade bending moments, simultaneously exhibiting no significant impact on the resulting power generation.

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].…”

“…Because of varying wind speed and inherent measurement noise, the PI-Observer estimates unknown disturbances and reconstructs the system state. The disturbance accommodation control compensates for the disturbance, fluctuating incoming wind, and regulates the power/speed of the wind turbine [19].…”

“…Here, the higher damage accumulation threshold will activate the controller with higher load mitigation capability. The gain scheduling module is able to monitor the damage accumulation so as to determine the changes in the operational ranges by varying the gain of the individual pitch controller [19]. This enables the proposed control scheme to be able to achieve a trade-off between structural load mitigation and power/speed regulation, thereby inhibiting premature failure before the expected lifetime.…”

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

“…A control strategy for extending the maintenance interval of wind turbine blades under assumed crack initiation, detected using a data filtering algorithm, is proposed (Beganovic et al, 2015). In (Beganovic et al, 2018;Njiri et al, 2019), a set of switching controllers with varying degrees of load mitigation are engaged sequentially based on the accumulated damage obtained from an online damage evaluation model to extend the lifetime of rotor blades. An adaptive lifetime controller is proposed in (Do and Söffker, 2019) to guaranty the desired lifetime of the tower.…”

“…Depending on the damage accumulation and the predicted lifetime provided by a online damage evaluation model, the weights of the lifetime controller are varied. However, in (Beganovic et al, 2015(Beganovic et al, , 2018Njiri et al, 2019;Do and Söffker, 2019) fatigue damage is considered in only one turbine component. The lifetime controllers used are not adaptive to varying wind conditions.…”