Abstract
In recent years the focus of wind energy industry is on reducing levelized cost of energy by rotor upscaling. Moreover, a current topic of interest to both industry and academia is the extension of lifetime to existing wind turbines approaching the end of initial design span. Thus, the need for load alleviation technologies integrated in the design process or for retrofit purposes is becoming more relevant. One of these is individual blade pitch control, a recurring topic in research, with known advantages and weaknesses namely the pitch actuator and bearing wear. The present work suggests such a system incorporating three independent controllers with input the root bending moments on the rotating frame. The linear system used for controller design is based on black box identification of non-linear simulations and filters are used both for the input and output. Different setups of the independent blade control scheme are applied on a 10 MW reference turbine, with a large and highly flexible rotor representative of the current industrial status, under wind conditions as defined by relevant certification standards. The investigation aims on evaluating the system’s performance based on the fatigue load alleviation potential for different components as well as identifying the tradeoff for each design choice. Finally, based on basic assumptions the reductions are translated to possible life time extension for each component based on a combined operation where the new controllers are applied for a percentage of the initial 20 year lifetime.
Highlights
The ongoing rapid growth in wind turbine rotor size leads to higher loads requiring more advanced load alleviation techniques
The baseline collective pitch controller (CPC) is a traditional controller for variable speed pitch regulated turbines with PI feedback for pitch and gain scheduling over pitch angle without any additional tower or drivetrain damping loops
Additional financial benefits can be considered, the present study focuses on the technical feasibility of the suggested business case
Summary
The ongoing rapid growth in wind turbine rotor size leads to higher loads requiring more advanced load alleviation techniques. Active and passive technologies could be major enablers in order to keep up this growth rate. Active control technologies [1] like individual pitch control (IPC) and smart rotors are more attractive since they offer more design freedom to load alleviation for different components. The life time extension possibilities for existing turbines is of high interest as installed capacity is increased and more projects are coming close to the end of design life [2], while new standards are being published for certification purposes [3] and major manufacturers already offer such service packages. Depending on the estimated remaining fatigue reserve of the different components the load alleviation from an updated controller with IPC, including possibly de-rating of the turbine, is a potential enabler for prolonging life time
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