Dynamic Behavior Of Wind Turbine Research Articles

Variable cross-sectional effect on bi-directional blades–tower–soil–structure dynamic interaction on offshore wind turbine subject to wind–wave loads

BackgroundThis study introduces a numerical model designed to simulate interactions occurring between a wind turbine's tower and the surrounding soil, as well as between the nacelle, blades, and the surrounding environment. This simulation accounts for both fore–aft and side-to-side movements. To describe these interactions, the model leverages the Euler–Lagrange equations. It calculates wave loads utilizing the Morison equation, with wave data generated based on the JONSWAP spectrum. Furthermore, aerodynamic loads are determined using the blade element moment theory, and the wind spectrum is generated using the Von Karman turbulence model. The tower is represented as a variable cross-sectional beam, employing a two-noded Euler beam element with two degrees of freedom: transverse displacement and rotation, and utilizing Hermite polynomial shape functions.ResultsIn a comparative analysis against experimental data, this modified model demonstrates significant enhancements in accurately reproducing the dynamic behavior of wind turbines with variable cross-sectional towers, outperforming models that approximate the tower with a constant cross section. Our findings reveal that the modified model achieves a remarkable improvement of 15% in replicating the tower's dynamic response when compared to the constant cross-sectional models. As a case study, a 5 MW monopile wind turbine with a flexible foundation, specifically the one provided by the National Renewable Energy Laboratory (NREL), is employed to simulate its dynamic response.ConclusionsThis research presents a robust numerical model for simulating wind turbine behavior in various environmental conditions. The incorporation of variable cross-sectional tower representation significantly improves the model's accuracy, making it a valuable tool for assessing wind turbine dynamics. The study's findings highlight the importance of considering tower flexibility in wind turbine simulations to enhance their real-world applicability.

A STUDY OF PERFORMANCE OF DFIG BASED MICROGRID SUBJECTED TO DISTURBANCES

The integration of wind energy into the electrical grid has become increasingly essential in our pursuit of sustainable and renewable energy sources. The research employs techniques to capture the complex dynamics of DFIG wind turbines, encompassing the rotor, drivetrain, and electrical subsystems. This analysis provides critical information for designing control strategies that enhance the stability and performance of grid-connected wind turbines. Furthermore, the inclusion of a detailed model allows us to investigate the mechanical aspects of the turbine. This holistic approach not only enhances our understanding of the system but also aids in the development of strategies to mitigate disturbance and improve the overall reliability of wind turbines. The findings of this study contribute to the optimization of grid connected DFIG wind turbines, making them more resilient and efficient in harnessing wind energy. As renewable energy sources continue to play a pivotal role in the global energy landscape, a comprehensive understanding of the dynamic behavior of wind turbines is essential for achieving a sustainable and reliable power supply. Key Words: MCDM; AHP; TOPSIS; MOORA; HRES.

WindPACT 1.5 MW Wind Turbine Rotor Dynamic Loads Under the Effect of Atmospheric Turbulence

The increasing demand for energy in the modern world, and the environmental effects of conventional energy sources, necessitate the need for renewable energy. Among the renewable energy sources, wind energy provides a clean and sustainable source of energy. Since the wind is of turbulent nature, the dynamic behaviour of wind turbines is highly affected by the turbulence intensity value. The study of dynamic loads and behaviour of wind turbine components is of crucial importance to making decisions regarding a wind turbine’s operation. In this work, the rotor dynamics of the WindPACT 1.5 MW wind turbine are studied under the influence of atmospheric turbulence. Four different wind fields with a mean wind speed value of 12 m/s, and turbulence intensities of 1%, 10%, 25% and 50% are simulated for the study. Rotor thrust force and torque are evaluated for each turbulence intensity. It was found that as the turbulence intensity increased, the fluctuations of the load around the mean value increased severely. For the rotor thrust, although the mean value is nearly unchanged, the standard deviation increases by 325% for the 50% turbulence intensity compared to the 1% intensity. An enormous increase in the rotor torque’s standard deviation occurs as well, for the 50% intensity compared to the 1% intensity, a 1300% increase occurs. The extremely high difference implies complications not only in the tower dynamics but also in the added cost of variable speed control continuously in operation. Continuous monitoring of wind speeds is highly recommended for the decision of putting the turbine into brake in such cases of severe turbulence.

Control and dynamic response analysis of full converter wind turbines with squirrel cage induction generators considering pitch control and drive train dynamics

This paper first deals with the control and dynamic modeling of full converter based wind turbines (WTs) with squirrel cage induction generator (SCIG) and then studies stability and dynamic behavior of WT considering the pitch angle control and drive train dynamics. In this way, WT system is divided into several single-input–single-output subsystems with several PI controllers, and control loops related to stator current, rotor flux, generator speed and pitch angle are extracted. Then, at the first stage, pitch angle control design based on the single-mass drive train model is presented, and WT dynamic performance is investigated by the modal and frequency response analyses of the whole WT system. It is shown that the control design based on the single mass model may result in unstable modes and thus unstable WT response. Next, theoretical analyses are developed for the elaborate pitch angle controller design using two-mass drive train model to consider torsional dynamics associated with the multi mass drive train model. Further, the paper examines the WT stability and interaction of the pitch control system with the speed control loop at different pitch control bandwidths. Finally, WT responses are studied by time domain simulations in the MATLAB-SIMULINK environment.

Dynamic behavior of wind turbines influenced by aerodynamic damping and earthquake intensity

AbstractIn the present paper the effects of aerodynamic damping and earthquake loads on the dynamic response of flexible‐based wind turbines are studied. A numerical analysis framework (NAF) is developed and applied. NAF is based on a user‐compiled module that is developed for the purposes of the present paper and is fully coupled with an open source tool. The accuracy of the developed NAF is validated through comparisons with predictions that are calculated with the use of different numerical analysis methods and tools. The results indicate that the presence of the aerodynamic loads due to the reduction of the maximum displacement of the tower attributed to the dissipation of earthquake excitation energy in fore‐aft direction. Emergency shutdown triggered by strong earthquakes results to a rapid change of aerodynamic damping, resulting to short‐term instability of the wind turbine. After shutdown of the wind turbine, enhanced dynamic response is observed. For the case where the wind turbine is parked, the maxima displacement and acceleration of tower‐top increase linearly with the peak ground acceleration. With the use of the least‐square method a dimensionless slope of tower‐top displacements is presented representing the seismic response coefficient of tower that can be used to estimate the tower‐top acceleration demand. Moreover, on the basis of the seismic response coefficient, an improved model for the evaluation of load design demand is proposed. This model can provide accurate predictions.

Dynamic behavior of wind turbines. An on-board evaluation technique to monitor fatigue

The evaluation of fatigue behavior of wind turbines, that is of supporting structures, blades or gear boxes, is always performed off-line, by post processing experimental acquisitions or simulation results. Moreover, the evaluation of potentiality of smart controls, that have the aim to avoid failures by reducing loads and consequently fatigue stresses, is performed in the same way.In this paper is presented a tool that allows to on-line evaluate and foresight fatigue potential damage by simply on time processing reference signals such as tower top acceleration (typical experimental acquisition) or tower base bending moment (typical numerical measure).This evaluation technique is converted into a well know numerical code, oriented to control systems (Simulink), to be used into multibody simulation by co-simulation approach. This step allowed to verify its capabilities and the possibility to realize its physical prototype and to use its results as input variable for active control strategies oriented to minimize damage.As test case a standard 5 MW wind turbine and a classical control logic were used.

Characterisation of wind speed series and power in Durban

Both the planning and operating of a wind farm demand an appropriate wind speed model of its location. The model also helps predict the dynamic behaviour of wind turbines and wind power potential in the location. This study characterises the wind speed series and power in Durban (29.9560°S, 30.9730°E), South Africa, using Markov chain and Weibull distribution. Comparison of statistical quantities of measured and Markov model-generated wind speed series revealed that the model accurately represented the measured wind speed series. The Markov model and Weibull distribution were also compared through their corresponding probability density functions. The root mean square error of the Markov model against the measured wind speed series was nearly one-tenth that of the Weibull distribution, indicating the effectiveness of the former. Finally, the analysis of wind power density showed that Durban and its environs need large wind turbines with hub heights greater than 85 m for efficient utilisation of the available wind energy.

Inverse Aerodynamic Optimization Considering Impacts of Design Tip Speed Ratio for Variable-Speed Wind Turbines

Because of the slow dynamic behavior of the large-inertia wind turbine rotor, variable-speed wind turbines (VSWTs) are actually unable to keep operating at the design tip speed ratio (TSR) during the maximum power point tracking (MPPT) process. Moreover, it has been pointed out that although a larger design TSR can increase the maximum power coefficient, it also greatly prolongs the MPPT process of VSWTs. Consequently, turbines spend more time operating at the off-design TSRs and the wind energy capture efficiency is decreased. Therefore, in the inverse aerodynamic design of VSWTs, the static aerodynamic performance (i.e., the maximum power coefficient) and the dynamic process of MPPT should be comprehensively modeled for determining an appropriate design TSR. In this paper, based on the inverse design method, an aerodynamic optimization method for VSWTs, fully considering the impacts of the design TSR on the static and dynamic behavior of wind turbines is proposed. In this method, to achieve higher wind energy production, the design TSR, chord length and twist angle are jointly optimized, which is structurally different from the conventional separated design procedure. Finally, the effectiveness of the proposed method is validated by simulation results based on the Bladed software.

Participation of DFIG Wind Turbine Controlled by Active Disturbance Rejection Control in Primary Frequency Control

In this article, we study control strategies enabling a variable speed of the wind turbine to participate in primary frequency control. The need for this participation is much stronger than the importance of the penetration of wind energy. These studied strategies based on control of the rotational speed of the generator and on the control of the pitch angle, allow to lower the power captured by the turbine so to maintain a reserve active power at all times according to the available maximum power. In case of frequency fault, these strategies increase or decrease the electrical power generated according to the variation of the grid frequency. The paper analyses the dynamic behavior of wind turbine at the primary frequency control for different wind speed values in Matlab-Simulink environment, and the performance of the implemented control strategies are studied.

Grid Code Requirements for Wind Power Integration in Europe

As the capacity of wind power continues to increase globally, stricter requirements regarding grid connection of wind generators are introduced by system operators. The development of wind turbine technology is inevitably affected by the new grid codes, and wind power plants are expected to support the grid and provide ancillary services much like conventional power plants. The most demanding regulations are found in Europe where wind penetration levels are higher. This paper presents the main aspects of current grid code requirements for the integration of wind power in European countries and suggests performance characteristics in order to satisfy the most demanding requirements. The dynamic behavior of wind turbines with doubly fed induction generators is investigated and a solution for low voltage ride through compliance is presented.

Farm Wide Dynamics: The Next Critical Wind Energy Frontier

The dynamic behaviour of wind turbines continues to be a major area of research in the wind power industry. Increasingly, wind turbines are grouped into large arrays that form farms capable of generating hundreds of megawatts of power. Farm wide dynamics refers to the collective behaviour of multiple wind turbines that cumulatively produces effects that cannot simply be modelled by summing the behaviours of individual machines. Many facets within this topic have been addressed singly in the literature and are widely used in industry; while others are less understood. It is here asserted that the farm wide dynamic approach is essential for the optimum design, power production, management, and profitability of a wind farm. The inter-relationships between the subcomponents of farm siting, power production, and maintenance are illustrated and discussed. A simple weighting system to assist in the prioritization of the critical dynamic elements is proposed.

Vibrations of wind-turbines considering soil-structure interaction

Wind turbine structures are long slender columns with a rotor and blade assembly placed on the top. These slender structures vibrate due to dynamic environmental forces and its own dynamics. Analysis of the dynamic behavior of wind turbines is fundamental to the stability, performance, operation and safety of these systems. In this paper a simplied approach is outlined for free vibration analysis of these long, slender structures taking the soil-structure interaction into account. The analytical method is based on an Euler-Bernoulli beam-column with elastic end supports. The elastic end-supports are considered to model the flexible nature of the interaction of these systems with soil. A closed-form approximate expression has been derived for the first natural frequency of the system. This new expression is a function of geometric and elastic properties of wind turbine tower and properties of the foundation including soil. The proposed simple expression has been independently validated using an exact numerical method, laboratory based experimental measurement and field measurement of a real wind turbine structure. The results obtained in the paper shows that the proposed expression can be used for a quick assessment of the fundamental frequency of a wind turbine taking the soil-structure interaction into account.

Feasibility of monitoring large wind turbines using photogrammetry

Abstract Photogrammetry, which is a proven measurement technique based on determination of the 3D coordinates of the points on an object by using two or more images taken from different positions, is proposed to be a promising and cost efficient alternative for monitoring the dynamic behavior of wind turbines. The pros and cons of utilizing this measurement technique for several applications such as dynamic testing or health monitoring of large wind turbines are discussed by presenting the results of the infield tests performed on a 2.5 MW - 80 m diameter - wind turbine. Within the scope of the work, the 3D dynamic response of the rotor is captured at 33 different locations simultaneously by using 4 CCD (charge coupled device) cameras while the turbine is rotating. Initial results show that the deformations on the turbine can be measured with an average accuracy of ±25 mm from a measurement distance of 220 m. Preliminary analyses of the measurements also show that some of the important turbine modes can be identified from photogrammetric measurement data.

Dynamic Behavior of Wind Turbine by a Mixed Flexible-Rigid Multi-Body Model

Dynamic Behavior of Wind Turbine by a Mixed Flexible-Rigid Multi-Body Model

Wind turbine dynamic response–difference between connection to large utility network and isolated diesel micro-grid

The difference in dynamic behaviour of wind turbines connected to different size networks is analysed for synchronous and induction generators. Modal analysis has been applied to equivalent mechanical models of the wind turbine generator and the grid connection to show the difference in dynamics for a wind turbine generator connected to a large (interconnected) utility network or an (isolated) diesel micro-grid. Frequency domain analysis of these models has been used to quantify the effect of system parameters, such as enhanced drive train damping, diesel governor action and generator slip, on dynamic interaction. It has been shown that for wind turbines connected to a large grid an induction generator can reduce dynamic interaction. In contrast, for an isolated diesel micro-grid the diesel governor response and the compliance of the diesel generator dominate the system's dynamics, and the choice of either generator option for the wind turbine is dictated by other factors.

Foundation modelling to assess dynamic behaviour of offshore wind turbines

The dynamic behaviour of wind turbines at offshore locations is more complex than that of both onshore wind turbines and offshore platforms used in the oil and gas industry. In order to reduce the computational burden, the work presented in this paper aims at simplification of the dynamic model of the foundation, while maintaining sufficient accuracy. A stiffness matrix at the mudline is found to be the best solution for monopiles. With respect to the required accuracy, the sensitivity of dynamic behaviour to variations in several parameters is investigated. An inaccuracy of about 4% can be expected for the first natural frequency. Finally, experimental data is used to determine whether expected accuracy is met in practice and whether modelling techniques, which are commonly used for offshore structures, can be used for wind turbines on monopile foundations. For five wind turbines in an offshore wind farm the results corresponded with expectations, but two wind turbines in another farm gave unexplained higher errors.

Analysis of a variable-speed wind energy conversion scheme with doubly-fed induction generator

In the last decade, the high penetration of wind turbines into the power system has been closely related to the advancement of wind turbine technology and control. The electric system contained by a large wind turbine, as well as within an offshore wind farm with hundreds of MW power capacity, has become more and more important in the interaction between the mechanical system of the wind turbine and the main power system. Furthermore, power electronics is entering the wind turbine circuitry which improves the controllability. The work presented in this paper has the main objective of extending the ability of the existing wind turbine design tools, in order to simulate the dynamic behaviour of wind turbines and the wind turbine–grid interaction.

International workshop: The dynamic behaviour of wind turbines : 28–30 April 1986, Sophia Antipolis (Alpes-Maritimes), France

International workshop: The dynamic behaviour of wind turbines : 28–30 April 1986, Sophia Antipolis (Alpes-Maritimes), France