Response Of Wind Turbine Research Articles

Enhancing the net energy of wind turbine using wind prediction and economic NMPC with high-accuracy nonlinear WT models

Economic nonlinear model predictive control (ENMPC) is a strong candidate for controlling wind turbines (WTs). In the model predictive control (MPC) group, the model is the crucial component for the true controller performance. It is common to use simplified models to reduce the problem complexity. These models neglect some of the underlying dynamic responses of real wind turbines. This paper simulates the case in which high accuracy nonlinear models describe both the plant and the controller. The results will be compared to reduced-order models in order to extract conclusions and decide the most appropriate model for WT control. On the other hand, one of the main features of MPC and ENMPC is the concept of receding prediction horizon, which considers the future evolution of the plant to compute the control action. The error of prediction will drastically reduce MPC performance. Also, rapid variation in wind speed can cause problems since wind turbines cannot easily follow these sudden variations due to their high inertia and aerodynamic characteristics. This paper provides an advanced control approach to improve the energy extraction from turbulent wind and enhance wind turbine durability. By implementing this method, the wind speed forecasting is done with a combination of artificial neural networks (ANN) and dynamic equations applied in ENMPC. The results show a significant enhancement of the control performance.

Effect of pulse-like near-fault ground motions on utility-scale land-based wind turbines

Seismic response of a utility-scale land-based wind turbine to near-fault pulse-like ground motions is presented in this study. The structural model corresponds to the 5-MW prototype developed by National Renewable Energy Laboratory. Response parameters such as tower-top displacement, base shear, and overturning moment are calculated by time history analysis and response spectral analysis using different estimates of response spectra. The results show that peak ground velocity and the frequency of dominant pulse of the ground motion are critical parameters governing the response, while peak ground acceleration has very weak correlation to response. When the pulse period is in the vicinity of structural period, seismic response is found to be much larger than those imposed by extreme events in design wind loads. Response spectral analysis using the actual spectra obtained from actual ground motions yielded results close to those from time history analysis. The spectral model prescribed in Eurocode8 is found to be inadequate in representing near-fault seismic action on the wind turbine.

Experimental and computational dynamic response comparison of hybrid and mono windmill towers considering soil–structure interaction

In countries like India, wind turbine heights are rapidly increasing to harvest more wind energy at a given location. In recent years, due to increase in hub height of windmill likelihood, soil lying below foundation may influence dynamic response of wind turbines. By increasing the height of the conventional monopole supporting system, it becomes slender and dynamically sensitive under the influence of soil below foundation; therefore, in the present investigation, hybrid supporting system is proposed to avoid slenderness effect of monopole system. A 1:40 scaled model of 78-m-high conventional monopole windmill and hybrid windmill comprised of nacelle, rotor mass and supporting tower are prepared in the laboratory. To study the behavior of both the towers under operational dynamic loads of rotor, laboratory tests were conducted on scaled model considering soil below foundation. Simulations of experimental analysis are presented for multi-degree of freedom turbine structure subjected to dynamic loading of rotor considering soil stiffness below base. It is examined in terms of displacement in time domain, shear at base of tower and response spectra. From laboratory tests and its simulation, it can be concluded that hybrid supporting system are recommended for windmill towers with higher hub heights considering soil stiffness below foundations.

Experimental and numerical study on the multi-body coupling dynamic response of a Novel Serbuoys-TLP wind turbine

The floating wind turbine (FWT) based on the tension leg platform (TLP) plays an important role in addressing the issue of energy pinch, but the central characteristic for TLP is that in vertical direction it is similar to a rigid structure with tension tendons to restrain motion, while in horizontal direction, it seems to be compliant with less constrain. The large amplitude motions in the horizontal plane caused by this compliance will seriously affect the performance of the platform under harsh environmental conditions. To address this problem, a new type of tension leg platform wind turbine connected with a series of buoys (Serbuoys-TLP) is proposed. A time-domain simulation program (DUTMST) for the TLP and Serbuoys-TLP based on MATLAB is provided, with consideration of the multi-body coupling effect between the body, tension leg and buoy. That is, each buoy can be analysed as a separate mass structure connected on the tension leg. The accuracy of DUTMST is discussed via comparison with the results of an experiment and AQWA. The dynamic responses of TLP and Serbuoys-TLP are presented in DUTMST. The results show that the Serbuoys-TLP can significantly reduce the horizontal response of the TLP. In addition, the horizontal response suppression effects of Serbuoys-TLP are investigated by varying the wave factor and parameters of buoys. Additionally, the parameters of buoys adapted to the East China Sea are given.

Modeling and analysis of grid-synchronizing stability of a Type-IV wind turbine under grid faults

Transient behavior and response of wind turbines have been extensively studied in the context of the low-voltage-ride-through (LVRT) for many years, in which the identified transients are mostly associated with circuit responses, whereas underlying stability issues relevant to converter control yet remain concealed. Recently, small-signal analyses of grid-tied converters have shown that the phase-locked-loop (PLL) may interact with other converter controls when synchronized to nonideal grids, if not properly treated, it may lead to oscillations. Enlightened by this, this paper will explore the PLL effects on the stability of a Type-IV wind turbine, however, from a large-signal analysis viewpoint. To achieve this, a nonlinear reduced-order model focusing on the transient interaction of PLL and the faulty grid is developed rigorously from the model assumption to verification. Based on this, the grid-synchronizing stability (GSS) provoked by grid faults is identified and the mechanism of which is revealed through the equal-area-principle (EAP). Then, impacts of system parameters (e.g. PLL bandwidth) on GSS margin are quantitatively evaluated by calculating the critical-clearing-time (CCT), and the acquired knowledge could be useful guidelines for PLL parameter design. Finally, all the analyses are verified by a switching model of the Type-IV wind turbine system in PSCAD/EMTDC.

Probabilistic analysis of offshore wind turbines under extreme resonant response: Application of environmental contour method

Offshore wind turbines can exhibit dynamic resonant behavior due to sea states with wave excitation frequencies coinciding with the structural eigenfrequencies. In addition to significant contributions to fatigue actions, dynamic load amplification can govern extreme wind turbine responses. However, current design requirements lack specifications for assessment of resonant loads, particularly during parked or idling conditions where aerodynamic damping contributions are significantly reduced. This study demonstrates a probabilistic approach for assessment of offshore wind turbines under extreme resonant responses during parked situations. Based on in-situ metocean observations on the North Sea, the environmental contour method is used to establish relevant design conditions. A case study on a feasible large monopile design showed that resonant loads can govern the design loads. The presented framework can be applied to assess the reliability of wave-sensitive offshore wind turbine structures for a given site-specific metocean conditions and support structure design.

Research on the Influence of Wind Characteristics on Output Characteristics of Doubly - fed Wind Turbines

The inherent randomness and intermittence of wind power will make it difficult to accurately predict the output of wind farms and the regulation and stability of power grids. As the output power of the turbine is proportional to the third power of the wind speed, tiny variation of the wind speed will cause much larger fluctuation of the turbine output. With the construction of wind farms gradually moving to non-wind resource-rich areas such as mountainous areas, wind turbines have to face more pulsating wind and greater turbulence intensity. In this paper, based on field measurement data and Generated wind conditions, a doubley-fed wind turbine simulation model was built to simulate the influence of different wind condition variations on the output characteristics of the doubly-fed wind turbines. The response of wind turbines to pulsating wind speed is analyzed by using the step response module to simulate the characteristics of wind. By dividing three different working intervals of wind turbine, the influence of different turbulence intensity on the output characteristics of wind turbines is analyzed. The simulation results have theoretical significance for improving the accuracy of wind turbine output prediction and wind turbine optimization design.

Vibration control of horizontal axis offshore wind turbine blade using SMA stiffener

Modern multi-megawatt wind turbines have large flexible blades that often exhibit significant vibration when exposed to turbulent wind. The present study proposes longitudinal stiffening of blades to address this issue using tendon made of shape memory alloy. A reduced order model of the combined system is developed that incorporates blade stiffening. The nonlinear material behavior of the stiffener is modeled by combining the principle of thermodynamics with the constitutive model as proposed in the literature. Thus, super-elastic effects are utilized in active mode (i.e. using Jule heating with the help of current flow) to apply actuation force that opposes blade deformation. Three-dimensional wind field passing through the rotor plane is simulated using TurbSim package freely available from National Renewable Energy Laboratory, USA. Aerodynamic loads are computed using modified Blade Element Momentum theory and wave loads are simulated using Morison’s equation where wave time histories are simulated from the JONSWAP spectrum. Using these loads as input, the response of a benchmark wind turbine is simulated to show the performance of the proposed control strategy. Numerical results presented in this paper clearly demonstrate the efficiency and advantage of the SMA based stiffener to improve the vibration characteristics of the large turbine blades.

Effect of foundation type and modelling on dynamic response and fatigue of offshore wind turbines

AbstractThis paper presents dynamic response and fatigue analyses of several bottom‐mounted offshore wind turbine (OWT) models, simulated in the aero‐hydro‐servo‐elastic simulation tool FAST. The distinction between the models is the foundations, which are modelled with different methods, concepts, and dimensions. The US National Renewable Energy Laboratory has developed a 5‐MW reference turbine supported on a monopile, the NREL 5MW, which was used as a reference model in this paper. The paper presents the implementation and comparison of two different foundation modeling methods, referred to as the simplified apparent fixity method and the improved apparent fixity method. Furthermore, sensitivity analyses of different monopile dimensions were performed, followed by sensitivity analyses of suction caisson foundations of different dimensions. The final part of the paper presents fatigue analyses for the foundation models considered in this study subjected to 17 load cases. Fatigue damage, fatigue life, and damage equivalent loads were calculated, as well as the relative fatigue contribution from each load case.

Implementation of Intelligent Algorithms for Pitch Angle and Output Power Control of Dfig Wind Turbine System.

The blade pitch angle is the vital part of wind energy system in getting desired output power. PID controller with the modified gains is considered as flexible and is administered for the regulation of blade pitch angle of turbine in this paper because of its lucidity, intermittent in its functionality and with easy usage in control system. FLC has powerful approach for collecting wind turbine response over PI controller where the speed and generator output power acting as input control variables for FLC with which these variables are evenly responsible to maintain proper aerodynamic power and its speed at rated value without any disturbance in output power and at gust speeds, the intelligent algorithms are been implemented to control the pitch angle upon adjusting the angle between the chord line of blades by adopting to new learning techniques as per the data collected. ANFIS had both the features of ANN and Fuzzy Logic Controllers by using Particle Swarm Optimization which gives the better response over the typical PI controller. This paper gives the information of supremacy of FOPID controller with PSO tuning over the other existing controllers. The dominance of the proposed method is made evident with the simulation results using 9MW WTS using MATLAB Simulink.

Adaptive filtering with robust controller for improvement of inertial response of wind turbine

Adaptive filtering with robust controller for improvement of inertial response of wind turbine

Dynamic response of a monopile wind turbine in waves: Experimental uncertainty analysis for validation of numerical tools

The responses of a monopile offshore wind turbine subjected to irregular wave loads are investigated numerically and experimentally, considering a range of sea states. An extensive experimental campaign was carried out on a fully flexible model, representative of a 5 MW offshore wind turbine, at 1:40 scale. An assessment of the experimental results for the response amplitude operator for regular waves and the 90th percentile seabed bending moment in long-crested irregular waves is carried out using two models (analytical and numerical) for uncertainty propagation, suggesting that bias errors in the model properties and in the wave elevation contribute the most to the total uncertainty. The experimental results are also compared to a numerical model using beam elements and Morison-type wave loads with second order wave kinematics. The numerical model does not capture all of the responses within the level of uncertainty of the experiments, and possible reasons for the discrepancies are discussed.

Aeroelastic Analysis of a Coplanar Twin-Rotor Wind Turbine

Multi-rotor system (MRS) wind turbines can be a competitive alternative to large-scale wind turbines. In order to address the structural behavior of the turbine tower, an in-house aeroelastic tool has been developed to study the dynamic responses of a 2xNREL 5MW twin-rotor configuration wind turbine. The developed tool has been verified by comparing the results of a single-rotor configuration to a FAST analysis for the same simulation conditions. Steady flow and turbulent load cases were investigated for the twin-rotor configuration. Results of the simulations have shown that elasticity of the tower should be considered for studying tower dynamic responses. The tower loads, and deformations are not straightforward with the number of rotors added. For an equivalent tower, an additional rotor will increase the tower-top deflection, and the tower-base bending moment both in the fore-aft direction will be more than doubled. The tower torsional stiffness becomes a crucial factor in the case of a twin-rotor tower to avoid a severe torsional deflection. Tower natural frequencies are dominant over the flow conditions in regards to the loads and deflections.

Smart Rotor With Trailing Edge Flap Considering Bend–Twist Coupling and Aerodynamic Damping: Modeling and Control

Aerodynamic damping and bend–twist coupling significantly affect the dynamic response of wind turbines. In this paper, unsteady aerodynamics, aerodynamic damping, and bend–twist coupling (twist-towards-feather) are combined to establish a smart rotor model with trailing edge flaps (TEFs) based on a National Renewable Energy Laboratory (NREL) 5 MW reference horizontal-axis wind turbine. The overall idea is to quantitatively evaluate the influence of aerodynamic damping and bend–twist coupling on the smart rotor and to present the control effect of the TEFs under normal wind turbine operating conditions. An aerodynamic model considering the dynamic stall and aerodynamic damping as well as a structural bend–twist coupling model with the influence of gravity and centrifugal force are incorporated into the coupling analysis. The model verification shows that the present model is relatively stable under highly unsteady wind conditions. Then, a robust adaptive tracking (RAT) controller is designed to suppress fluctuations in both the flapwise tip deflection and output power. The simulations show an average reduction of up to 63.86% in the flapwise tip deflection power spectral density (PSD) of blade 1 at the 1P frequency, with an average reduction in the standard deviation of the output power of up to 34.33%.

Optimised de-rated wind turbine response and loading through extended controller gain-scheduling

An increasing number of wind turbines are expected to be able to participate in the ancillary services that would normally be provided by conventional power plants, as the penetration of the wind energy in the electricity grid is increasing. Specifically, the turbines are needed to be able to control their active power based on the operator command. Constraining the possible output power, i.e. decreasing the power to less than the maximum or rated power, is therefore important for the wind turbine control system. When a turbine is operating under a de-rating strategy, the operating points of the turbine, i.e. the steady-state blade pitch and the tip speed ratio, change compared to the normal case and this needs to be considered within the controller design. Thus, this paper is to study the influence of the de-rating on the turbine controller gain-scheduling and its effect to power output and fatigue damage of the key turbine components. The results show that the wind turbine response is refined through tuning under the different down-regulation operation points, that translate into less fatigue damage of the key turbine components. For a typical multi-megawatt turbine, it is found that the main component lifetime damage can be reduced substantially. In numerical terms, there are up to 6.5% for the tower BM in fore-aft direction and 2.7% for the blade root flapwise direction, which can lead in a prolonged operational lifetime of the wind turbine.

Research on Robust Day-Ahead Dispatch Considering Primary Frequency Response of Wind Turbine

With the large-scale integration of renewable energy sources (e.g., wind power), the system inertial response and primary frequency regulation are affected. The virtual synchronous generator technology, which makes it possible for wind power units to adjust the frequency, provides a new way of approaching this problem. In this paper, we set up the related constraints that fit the optimal dispatch framework with a primary reserve representing the primary frequency response between the conventional synchronous generator and the wind power units, and the technical parameters of the virtual synchronous generator. Meanwhile, we use the robust day-ahead optimization dispatch model considering the wind power integrated primary frequency control in the real-time operation with the scenario of the wind power output showing the uncertainty of wind power. Based on the model, we identify the key set using an iterative method and obtain the maximum power loss. Through the proposed model, we could provide the day-ahead unit output and real-time primary reserve, thus ensuring the reliable operation of the system. Finally, the effectiveness of the proposed method is verified by a computational experiment.

Nonlinear Aeroelastic Analysis of Large Wind Turbines Under Turbulent Wind Conditions

We investigate in this Paper the nonlinear aeroelastic response of large horizontal axis wind turbines under a stochastically simulated turbulent wind field, which is instantaneously sampled by the rotating and deforming blades of the rotor. The aeroelastic code combines the unsteady blade element momentum theory, equipped with several important corrections, with the displacement-based nonlinear finite element implementation of the geometrically exact beam theory. The structural model is both shearable and extensible and does not place any restrictions on the magnitudes of the configuration variables or those of the resulting one-dimensional strain measures. The aeroelastic coupling takes into account the beam axis deformations, elastic twist, and vibration-induced velocities. The three-component, three-dimensional turbulent wind field is obtained using the Mann spectrum, from which the instantaneously sampled wind speeds are extracted by spatiotemporal interpolation in the spirit of Taylor’s frozen turbulence hypothesis. The structural and unsteady aerodynamic analysis components of the aeroelastic code are validated using benchmark examples. A fully coupled nonlinear aeroelastic simulation is carried out for the National Renewable Energy Laboratory’s 5 MW research wind turbine. The influence of three-dimensional instantaneous sampling, transverse (lateral and vertical) components of turbulence, vertical wind shear, and flow unsteadiness on the aeroelastic response under turbulence is examined along with the effects of coupling parameters including the vibration-induced velocities and elastic twist of the rotor blades. The dominant frequency contributions in key aeroelastic response variables due to each of these effects are identified.

Influence of earthquake ground motion modelling on the dynamic responses of offshore wind turbines

Offshore wind turbines (OWTs) are more and more widely used to produce electrical energy nowadays. Besides the constant wind and wave loads, earthquake excitation can be another important vibration source to the OWTs since many OWTs have been/will be constructed in the seismic prone areas. Extensive research works have been carried out to understand the dynamic behaviours of OWTs when they are subjected to multi-hazards (e.g. the simultaneous wind, wave and/or earthquake loadings). However, when seismic excitations are considered, the onshore earthquake records are normally used as inputs in the analyses due to the lack of offshore data and the difficulty in synthesizing the offshore seismic motions. This practice may lead to inaccurate structural response estimations since it is well known that the seawater can significantly suppress the seafloor vertical motions near the P wave resonant frequencies of the seawater layer, which in turn results in the different characteristics of onshore and offshore earthquake recordings. Moreover, the earthquake motions along the pile of OWTs are different from those at the ground surface, i.e. the earthquake motions vary with the soil depth. Recently, a method to stochastically simulate the earthquake ground motions on the offshore site was proposed, in which the influence of seawater layer was considered and the earthquake motions at any soil depth could be obtained. This paper carries out numerical simulations on the dynamic behaviours of OWTs subjected to the combined wind, wave and earthquake loadings, and the depth-varying offshore seismic motions are used as inputs in the analyses. The seismic responses of OWTs obtained from the onshore and offshore earthquake motions are calculated and compared. The influence of depth-varying ground motions on the dynamic responses of OWTs is discussed.

Analysis of seismic behaviour of an offshore wind turbine with a flexible foundation

This paper investigates the effects of nonlinear soil behaviours on the structural responses of offshore wind turbines (OWTs) subjected to wind, wave and earthquake loadings. A novel seismic analysis framework (SAF) is developed for the assessment of seismic behaviours of OWTs with flexible and fixed foundations. The SAF consists of an improved QuakeDyn module that is implemented into an open source tool (FAST). SAF has been validated through benchmark studies using numerical tools and the results show good agreements. Fully coupled nonlinear simulations have been performed for OWTs with fixed and flexible foundations under operational, parked and emergency shutdown states. The flexible foundation is modelled using nonlinear p-y curves obtained using LPILE. For all the examined operating conditions, notable differences of magnitude and variation in the responses between the flexible and fixed cases are observed, indicating the need for soil effects to be accounted in seismic behaviour analysis of wind turbines. It is further observed that the earthquake induces more severe vibrations on wind turbines with a flexible foundation compared to the one with a fixed base. Also, aerodynamic damping dissipates more energy from earthquake excitation resulting in a smaller tower-top fore-aft displacement. The shutdown triggered by the earthquake causes a 34% increase in the mudline bending moment for the flexible foundation case, while a decreasing trend is observed for the fixed foundation model. Similar observations are made regarding the tower-top displacements. The observations imply that ignoring the soil effect may lead to misjudgement of the consequence of an emergency shutdown. The relative orientation of the ground motion with respect to the wind direction causes significant difference in the seismic behaviour of the wind turbine. This confirms that it is necessary to interchange the horizontal components of an earthquake in order to consider the intersectional effect between ground motion and wind.

Loads and Response of a Tension Leg Platform Wind Turbine with Non-Rotating Blades: An Experimental Study

This paper describes model testing of a Tension Leg Platform Wind Turbine (TLPWT) with non-rotating blades to better understand its motion and tendon responses when subjected to combined wind and unidirectional regular wave conditions. The TLPWT structure is closely based on the National Renewable Energy Laboratory (NREL) 5 MW concept. Multiple free decay tests were performed to evaluate the natural periods of the model in the key degrees of freedom, whilst Response Amplitude Operators (RAOs) were derived to show the motion and tendon characteristics. The natural periods in surge and pitch motions evaluated from the decay tests had a relatively close agreement to the theoretical values. Overall, the tested TLPWT model exhibited typical motion responses to that of a generalised TLP with significant surge offsets along with stiff heave and pitch motions. The maximum magnitudes for the RAOs of surge motion and all tendons occurred at the longest wave period of 1.23 s (~13.0 s at full-scale) tested in this study. From the attained results, there was evidence that static wind loading on the turbine structure had some impact on the motions and tendon response, particularly in the heave direction, with an average increase of 13.1% in motion amplitude for the tested wind conditions. The wind had a negligible effect on the surge motion and slightly decreased the tendon tensions in all tendons. The results also showed the set-down magnitudes amounting to approximately 2–5% of the offset. Furthermore, the waves are the dominant factor contributing to the set-down of the TLPWT, with a minimal contribution from the static wind loading. The results of this study could be used for calibrating numerical tools such as CFD codes.