965 research outputs found
Wind turbines controllers design based on the super-twisting algorithm
The continuous increase in the size of wind turbines (WTs) has led to new challenges in the design of novel torque and pitch controllers. Todayâs WT control design must fulfill numerous specifications to assure effective electrical energy production and to hold the tower vibrations inside acceptable levels of operation. Hence, this paper presents modern torque and pitch control developments based on the super-twisting algorithm (STA) by using feedback of the fore- aft and side-to-side acceleration signals of the WT tower. According to numerical experiments realized using FAST, these controllers mitigate vibrations in the tower without affecting the quality of electrical power production. Moreover, the proposed controllersâ performance is better than the baseline controllers used for comparison.Postprint (author's final draft
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Effects of soilâstructure interaction on the design of tuned mass damper to control the seismic response of wind turbine towers with gravity base
This paper studies the effect of soilâstructural interaction (SSI) on gravityâbased wind turbine towers equipped with tuned mass dampers (TMDs) subjected to earthquake loading. A smallâscale shaking table test of wind turbine towers with TMD was conducted, and the results showed that using TMD designed considering SSI resulted in larger vibration suppression. A simplified analytical numerical model was developed for SSI analysis considering TMD. The effect of soil site class and the earthquake intensity on the response reduction efficiency of the TMD was also discussed using the simplified model. It is concluded that the TMD efficiency depends not only on the soil stiffness but also on the characteristics of the applied ground motions, both of which are affected by the site classes and earthquake intensity levels. Moreover, the peak acceleration ratio (PAR), the root mean square acceleration ratio (RAR), the peak displacement ratio (PDR), and the root mean square displacement ratio (RDR) of the top of the wind turbine tower were obtained with and without TMD for different earthquake intensities and sites. These parameters can be used as references for the rational selection of TMD parameters considering SSI
Load reduction of a monopile wind turbine tower using optimal tuned mass dampers
We investigate to apply tuned mass dampers (TMDs) (one in the foreâaft direction, one in the sideâ side direction) to suppress the vibration of a monopile wind turbine tower. Using the spectral element method, we derive a finite-dimensional state-space model d from an infinite-dimensional model d of a monopile wind turbine tower stabilised by a TMD located in the nacelle. and d can be used to represent the dynamics of the tower and TMD in either the foreâaft direction or the sideâ side direction. The wind turbine tower subsystem of is modelled as a non-uniform SCOLE (NASA Spacecraft Control Laboratory Experiment) system consisting of an EulerâBernoulli beam equation describing the dynamics of the flexible tower and the NewtonâEuler rigid body equations describing the dynamics of the heavy rotor-nacelle assembly (RNA) by neglecting any coupling with blade motions. d can be used for fast and accurate simulation for the dynamics of the wind turbine tower as well as for optimal TMD designs. We show that d agrees very well with the FAST (fatigue, aerodynamics, structures and turbulence) simulation of the NREL 5-MW wind turbine model. We optimise the parameters of the TMD by minimising the frequency-limited H2-norm of the transfer function matrix of d which has input of force and torque acting on the RNA, and output of tower-top displacement. The performances of the optimal TMDs in the foreâaft and sideâside directions are tested through FAST simulations, which achieve substantial fatigue load reductions. This research also demonstrates how to optimally tune TMDs to reduce vibrations of flexible structures described by partial differential equations
Fragility reduction of offshore wind turbines using tuned liquid column dampers
High flexibility of offshore wind turbines (OWTs) makes them vulnerable to excessive vibrations. This paper studies vibration control of offshore wind turbines induced by multi-hazard excitations. A model consisting of entire offshore wind turbine foundation and tower controlled by tuned liquid column dampers(TLCD) considering nonlinear soil pile interaction is established. The model is subjected to wave, wind, and seismic loading. The effect of severity of earthquake on the performance of the structural control device is investigated. A fragility analysis based on acceleration capacity thresholds is performed to estimate reliability improvement using the structural control devices. The fitted fragility functions based on multiple stripes analysis are constructed and compared with the empirical cumulative distribution curves. The results suggest that the use of an optimal TLCD with a mass ratio of 2.5% reduces the fragility of the system by as much as 6% and 12% for operational and parked conditions, respectively
Fluid inerter for optimal vibration control of floating offshore wind turbine towers
This paper proposes the use of a tuned mass damper fluid-inerter (TMDFI) for vibration control of spar-type floating offshore wind turbine towers. The use of an inerter in parallel with the spring and damper of a tuned mass damper (TMD) is a relatively new concept. The ideal inerter has a mass amplification effect on the classical TMD leading to greater vibration control capabilities. Previous work by the authors has shown that inerter based TMDs have great potential in vibration control of floating offshore wind turbines where enhanced vibration mitigation can be achieved using a relatively lighter device than classical TMDs. However, this previous work was based on the assumption of an ideal inerter that assumes the use of a mechanical flywheel type inerter. Mechanical inerters have some inherent disadvantages due to their complexity in design and high cost of maintenance. The use of a fluid inerter can alleviate these disadvantages as its design is rather simple and it comes with very low maintenance. Such devices have been proposed and investigated in the literature, however, their applicability in vibration control of floating wind turbines has not been investigated by researchers. The optimal design of a TMDFI is presented in this paper. It has been shown that optimization of a TMDFI is a six-dimensional non-linear optimization problem whose solution hyperplane contains multiple local minima. A systematic way has been developed in this paper, avoiding the use of metaheuristic search techniques, to optimize the damper while providing greater insight into the damper properties that offers a set of guidance to the designer. Numerical results demonstrate impressive vibration control capabilities of this new device under various stochastic wind-wave loads. It has been shown that the fluid-inerter performs as well as the ideal mechanical inerter. The considerable advantages of a TMDFI over the classical TMD demonstrated in this paper makes it an exciting candidate for vibration control
Strong stabilization of a wind turbine tower model in the plane of the turbine blades
We investigate the strong stabilization of a wind turbine tower model in the plane of the turbine blades, which comprises a nonuniform SCOLE system and a two-mass drive-train model (with gearbox). The control input is the torque created by the electrical generator. Using a strong stabilization theorem for a class of impedance passive linear systems with bounded control and observation operators, we show that the wind turbine tower model can be strongly stabilized. The control is by static output feedback from the angular velocities of the nacelle and the generator rotor
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Floating Offshore Wind Turbines Oscillations Damping.
This article deals with the modelling and control of oscillations that appear on floating offshore wind turbines (FOWT). First, these offshore wind energy systems, located in deep waters, are described and the modeling approach is presented. Secondly, the traditional structural control strategies based on tuned mass-damper (TMD) systems for oscillations reduction are complemented with a passive mechanism called inerter in order to improve the performance of the structural controller. This work is based on a previous work by the authors in which the inerter was located in parallel to an existing TMD in the nacelle of the FOWT. In this work, the inerter is located between the tower and the barge and results are compared to those obtained previously showing better performance. The results here presented are promising in terms of oscillations damping, both in amplitude and frequency, and constitute preliminary results of the ongoing current research of the authors
Vibration suppression of offshore wind turbine foundations using tuned liquid column dampers and tuned mass dampers
Highly dynamic nature of the applied loads on flexible and lightly damped offshore wind turbine (OWT) foundations affects the lifetime and serviceability of the system. In this study, the excessive vibration responses of OWTs are minimized using tuned mass dampers (TMD) and tuned liquid column dampers (TLCD). Due to high efficiency of TLCDs and TMDs for certain loading conditions, a combined TLCD-TMD is also utilized to improve the overall performance in a wide range of loading conditions. First, a parametric study was performed that highlights the sensitivity of these structural control devices. The effect of two devices on fixed offshore wind turbine foundations for the benchmark 5MW NREL turbine in various loading patterns was investigated. Then, the model was subjected to stochastically generated wind loading in operational, parked, startup, and shutdown conditions. The results suggest that the standard deviation of the dynamic responses can be greatly reduced with all structural control devices. However, TMDs are more efficient in operational conditions, whereas TLCDs show better performances in parked conditions. This highlights the possibility and efficiency of a combined TLCD-TMD system in which the dynamic responses are minimized efficiently in a wider selection of loading conditions
Modelling and control of coupled infinite-dimensional systems
First, we consider two classes of coupled systems consisting of an infinite-dimensional
part [sigma]d and a finite-dimensional part [sigma]f connected in feedback. In the first class of coupled
systems, we assume that the feedthrough matrix of [sigma]f is 0 and that [sigma]d is such that
it becomes well-posed and strictly proper when connected in cascade with an integrator.
Under several assumptions, we derive well-posedness, regularity and exact (or approximate)
controllability results for such systems on a subspace of the natural product state
space. In the second class of coupled systems, [sigma]f has an invertible first component in its
feedthrough matrix while [sigma]d is well-posed and strictly proper. Under similar assumptions,
we obtain well-posedness, regularity and exact (or approximate) controllability results as
well as exact (or approximate) observability results for this class of coupled systems on
the natural state space.
Second, we investigate the exact controllability of the SCOLE (NASA Spacecraft Control
Laboratory Experiment) model. Using our theory for the first class of coupled systems,
we show that the uniform SCOLE model is well-posed, regular and exactly controllable
in arbitrarily short time when using a certain smoother state space.
Third, we investigate the suppression of the vibrations of a wind turbine tower using
colocated feedback to achieve strong stability. We decompose the system into a
non-uniform SCOLE model describing the vibrations in the plane of the turbine axis,
and another model consisting of a non-uniform SCOLE system coupled with a two-mass drive-train model (with gearbox), in the plane of the turbine blades. We show the strong
stabilizability of the first tower model by colocated static output feedback. We also prove
the generic exact controllability of the second tower model on a smoother state space
using our theory for the second class of coupled systems, and show its generic strong
stabilizability on the energy state space by colocated feedback
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