This paper describes the formulation and verification of a novel observer of wind parameters. The general idea behind the proposed approach is to consider the wind turbine rotor as an anemometer. In ...fact, the rotor responds to varying wind conditions; by properly interpreting this response, one can indirectly measure some desired wind characteristics, as for example yaw and shear, as described here.
Measurements of wind conditions obtained this way are not affected by the usual disturbances of existing sensors, for example when installed in the nacelle or in the rotor wake. Furthermore, the approach provides rotor-equivalent quantities, and not the typical point information provided by wind vanes, anemometers or other similar sensors, whose information might be too local for large rotors.
The proposed method is here formulated for the observation of wind direction and vertical shear. The new observer is demonstrated first in a comprehensive simulation study using high-fidelity aeroservoelastic models, and then experimentally using an aeroelastically-scaled wind tunnel model.
•Estimation of wind shear and wind misalignment.•Estimation of rotor-effective wind characteristics, in contrast to the local information provided by standard sensors.•Estimator uses only blade root loads.•Demonstration in a high-fidelity simulation environment.•Further verification using an aeroelastically-scaled model in a wind tunnel.
This work focuses on the design of wind turbine rotors of wind tunnel size that match the aerodynamic (for both rotor and wake) and aeroelastic behavior of multi-MW machines, including gravitational ...effects. The approach follows the classical definition of length, time and mass scaling ratios to respect nondimensional scaling parameters. The sub-scale model is obtained by a complete aero-structural re-design procedure, considering airfoils with similar polars at sub-scale Reynolds and the use of adequate materials. The approach is applied to the design of a sub-scale wind tunnel rotor that mimics the behavior of a 10 MW wind turbine. Results illustrate the main characteristics of the proposed method as well as its limitations, highlighting the challenges posed by representing a gravo-aeroelastic system at a much reduced scale.
A previously described observer of wind misalignment is validated using field test data collected on the NREL CART3 wind turbine. The observer uses blade root bending moment 1P harmonics, computed ...using the transformation of Coleman and Feingold, to infer the rotor-equivalent relative wind direction. The observation model parameters are determined by a least squares fitting using recorded blade loads and met-mast measured wind direction and speed; a random sample consensus (RANSAC) algorithm is used to robustify the parameter estimation procedure while detecting outliers in the experimental samples. The observer is validated using an independent verification data set: recorded blade bending loads are fed to the observer and the estimated wind misalignment is compared to both the one provided by the met-mast vanes, assumed as the ground truth, and by an on-board nacelle-mounted wind vane. Results show that the rotor-equivalent wind misalignment estimates provided by the proposed observer are well correlated in the low frequency spectrum with the met-mast reference, and in general are in much better accordance with it than the on-board wind vane measurements.
•Wind observer provides rotor-equivalent wind misalignment information, to be used for wind turbine yaw control.•Observer uses blade loads, wind speed and rotor azimuth, all quantities typically already available on modern wind turbines.•Model-free approach, uses field test data to build observation model.•NREL CART3 wind turbine field data is used for model validation.•Observed wind misalignment is better correlated with met-mast measurements than the on-board wind vane.
In this paper, the turbine itself is used as an anemometer to estimate the inflow at its rotor disk. Indeed, given that any anisotropy in the wind will lead to periodic loads, by studying the machine ...response one can infer rotor-effective wind conditions and exploit such information for turbine and farm-level control applications. Specifically, expanding the idea of previous publications, the case of an individually pitch-controlled machine is considered herein: a linear implicit model is formulated to relate some characteristics of the wind -in the form of shears and misalignment angles- to the 1P harmonics of pitch angles and blade loads. The performance of the proposed algorithm is tested in a simulation environment, including both uniform and turbulent wind conditions.
This paper considers the problem of power regulation for a variable speed wind turbine in the presence of a blade tip speed constraint, for example to limit noise emissions. The main contribution of ...the paper is the formulation of a policy for the regulation of the machine in the transition region between the classical regions
II and
III that accommodates the tip speed constraint, and the derivation of associated wind schedules for the rotor speed, blade pitch and aerodynamic torque. To exemplify the possible use of such wind schedules in the design of control laws, model-based controllers are formulated in this paper that are capable of performing power curve tracking throughout all wind speeds, in contrast with commonly adopted approaches that use switching controllers to cover the various operating regimes of the machine. The proposed regulation policies and control laws are demonstrated in a high fidelity simulation environment for a representative 3 MW machine.
► Power optimization in the presence of a rotor speed constraint. ► Smooth transition between operating regions of controller. ► No switching logics. ► Wind-driven schedules, implemented through a wind observer.
We describe a multi-layer architecture for the control of variable speed wind turbines, whereby each control layer targets a specific goal. The proposed architecture is inspired by the ...multi-objective nature of the wind turbine control problem.
Three main goals are identified and associated with three distinct control loops: a) trimming and load alleviation for large scale gusts engulfing the whole rotor disk, targeted by a collective-pitch/torque controller; b) alleviation of deterministic slowly varying and low frequency loads, targeted by a higher harmonic controller operating in the frequency domain; and c) alleviation of non-deterministic loads caused by small spatial and fast temporal wind fluctuation due to turbulence.
The proposed control architecture is demonstrated by means of various tests conducted in a high-fidelity simulation environment.
► Higher harmonic individual blade pitch control. ► Multi-objective approach to control synthesis. ► Targets deterministic and non-deterministic loads. ► Demonstration in a high fidelity simulation environment.
We study the problem of deforming unstructured grids using pseudo-structural lumped-parameter systems. A basic network of edge springs is complemented with an additional set of linear springs that ...oppose element collapsing. This is here achieved by confining each mesh vertex to its ball, through linear springs that are attached to the vertex and to its projections on the ball entities. The resulting linear pseudo-structural problem can be solved efficiently with an iterative method. The proposed procedures are compared with a revisited version of the torsional spring method with the help of two and three-dimensional example problems.
We present a novel planning strategy which is applicable to high performance unmanned aerial vehicles. The proposed approach takes as input a 3-D sequence of way-points connected by straight flight ...trim conditions, and ldquosmoothsrdquo it in an optimal way with the goal of making it compatible with the vehicle dynamics. The smoothing step is achieved by selecting appropriate sequences of alternating trims and maneuvers from within a precomputed library of motion primitives. The resulting extremal trajectory is compatible with the vehicle and therefore trackable with small errors; furthermore, it is guaranteed to stay within the flight envelope boundary, alleviating the need for flight envelope protection systems. Yet it can be computed in real-time using closed-form expressions, all nonlinearities due to the vehicle model being confined to the stored library of motion primitives. The new method is demonstrated for the aggressive maneuvering of a helicopter.
Having an improved awareness of the flow within a wind farm is useful for power harvesting maximization, load minimization and design of wind farm layout. Local flow information at each wind turbine ...location can be obtained by using the response of the wind turbines, which are consequently used as distributed sensors. This paper proposes the use of hub loads to track the position of wakes within a wind farm. Simulation experiments conducted within a high-fidelity aeroservoelastic environment demonstrate the performance of the new method.
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