Showing papers on "Turbine published in 2016"

Wind plant power optimization through yaw control using a parametric model for wake effects—a CFD simulation study

Abstract: This article presents a wind plant control strategy that optimizes the yaw settings of wind turbines for improved energy production of the whole wind plant by taking into account wake effects. The optimization controller is based on a novel internal parametric model for wake effects called the FLOw Redirection and Induction in Steady-state (FLORIS) model. The FLORIS model predicts the steady-state wake locations and the effective flow velocities at each turbine, and the resulting turbine electrical energy production levels, as a function of the axial induction and the yaw angle of the different rotors. The FLORIS model has a limited number of parameters that are estimated based on turbine electrical power production data. In high-fidelity computational fluid dynamics simulations of a small wind plant, we demonstrate that the optimization control based on the FLORIS model increases the energy production of the wind plant, with a reduction of loads on the turbines as an additional effect. Copyright © 2014 John Wiley & Sons, Ltd.

Experimental and theoretical study of wind turbine wakes in yawed conditions

Abstract: This work is dedicated to systematically studying and predicting the wake characteristics of a yawed wind turbine immersed in a turbulent boundary layer. To achieve this goal, wind tunnel experiments were performed to characterize the wake of a horizontal-axis wind turbine model. A high-resolution stereoscopic particle image velocimetry system was used to measure the three velocity components in the turbine wake under different yaw angles and tip-speed ratios. Moreover, power and thrust measurements were carried out to analyse the performance of the wind turbine. These detailed wind tunnel measurements were then used to perform a budget study of the continuity and Reynolds-averaged Navier–Stokes equations for the wake of a yawed turbine. This theoretical analysis revealed some notable features of the wakes of yawed turbines, such as the asymmetric distribution of the wake skew angle with respect to the wake centre. Under highly yawed conditions, the formation of a counter-rotating vortex pair in the wake cross-section as well as the vertical displacement of the wake centre were shown and analysed. Finally, this study enabled us to develop general governing equations upon which a simple and computationally inexpensive analytical model was built. The proposed model aims at predicting the wake deflection and the far-wake velocity distribution for yawed turbines. Comparisons of model predictions with the wind tunnel measurements show that this simple model can acceptably predict the velocity distribution in the far wake of a yawed turbine. Apart from the ability of the model to predict wake flows in yawed conditions, it can provide valuable physical insight on the behaviour of turbine wakes in this complex situation.

Wind turbine wake models developed at the technical university of Denmark: A review

Abstract: Wind turbine wakes are one of the most important aspects in wind power meteorology because they decrease the power production and increase the loading of downstream wind turbines. Therefore, there is a continuous need to find a ‘good’ wake model to properly plan wind power plant-level control strategies, predict the performance and understand the fatigue loads of turbines. In this paper, six widely used approaches of wake modelling (Jensen, Larsen, Dynamic Wake Meandering, Fuga and, Ellipsys3D LES and RANS together with their interpretations) that were developed at Technical University of Denmark, are described and the model subcomponents are analysed. The models are evaluated using data from the Sexbierum (onshore) and the Lillgrund (offshore) wind farms to understand how to best utilize them. The paper provides a comprehensive conceptual background to wake modelling combined with the overview of the state-of-the-art models including their implementations on operating wind farms.

A review of wind turbine bearing condition monitoring: State of the art and challenges

Abstract: Since the early 1980s, wind power technology has experienced an immense growth with respect to both the turbine size and market share. As the demand for large-scale wind turbines and lor operation & maintenance cost continues to raise, the interest on condition monitoring system has increased rapidly. The main components of wind turbines are the focus of all CMS since they frequently cause high repair costs and equipment downtime. However, vast quantities of their failures are caused due to a bearing failure. Therefore, bearing condition monitoring becomes crucial. This paper aims at providing a state-of-the-art review on wind turbine bearing condition monitoring techniques such as acoustic measurement, electrical effects monitoring, power quality, temperature monitoring, wear debris analysis and vibration analysis. Furthermore, this paper will present a literature review and discuss several technical, financial and operational challenges from the purchase of the CMS to the wind farm monitoring stage.

State-of-the-art in wind turbine control: Trends and challenges

Abstract: Wind energy is one of the most rapidly growing renewable sources of energy due to the fact that it has little negative impact on environment. To meet the growing demand, wind turbines are being scaled up both in size and power rating. However, as the size increases, the structural loads of the turbine become more dominant, causing increased fatigue stress on the turbine components which can lead to early failure. Another area of focus in wind energy is lowering production cost to give it a competitive edge over other alternative power sources. From the control point of view, low production cost of wind energy can be achieved by operating the wind turbine at/or near the optimum power efficiency during partial load regime, guaranteeing reliability by reducing fatigue loads, and regulating generated power to its rated value in the high wind regime. Often, it is difficult to realize a control algorithm that can guarantee both efficiency and reliability because these two aspects involve conflicting objectives. This paper reviews various control strategies that are used in wind turbine systems, both in low and high wind speed regions focusing primarily on multi-objective control schemes. Emerging trends that are likely to influence the current or future wind energy production, either positively or negatively, are also discussed.

Sliding Mode Control of PMSG Wind Turbine Based on Enhanced Exponential Reaching Law

Abstract: This paper proposes a sliding-mode control (SMC)-based scheme for the variable-speed direct-driven wind energy conversion systems (WECS) equipped with a permanent magnet synchronous generator connected to the grid. In this paper, diode rectifier, boost converter, neutral point clamped inverter, and L filter are used as the interface between the wind turbine and grid. This topology has abundant features such as simplicity for low- and medium-power wind turbine applications. It is also less costly than back-to-back two-level converters in medium-power applications. The SMC approach demonstrates great performance in complicated nonlinear systems control such as WECS. The proposed control strategy modifies reaching law (RL) of the sliding mode technique to reduce chattering issue and to improve total harmonic distortion property compared to conventional RL SMC. The effectiveness of the proposed control strategy is explored by simulation study on a 4-kW wind turbine, and then verified by experimental tests for a 2-kW setup.

Wake structure in actuator disk models of wind turbines in yaw under uniform inflow conditions

Abstract: Reducing wake losses in wind farms by deflecting the wakes through turbine yawing has been shown to be a feasible wind farm controls approach. Nonetheless, the effectiveness of yawing depends not only on the degree of wake deflection but also on the resulting shape of the wake. In this work, the deflection and morphology of wakes behind a porous disk model of a wind turbine operating in yawed conditions are studied using wind tunnel experiments and uniform inflow. First, by measuring velocity distributions at various downstream positions and comparing with prior studies, we confirm that the non-rotating porous disk wind turbine model in yaw generates realistic wake deflections. Second, we characterize the wake shape and make observations of what is termed as curled wake, displaying significant spanwise asymmetry. The wake curling observed in the experiments is also reproduced qualitatively in Large Eddy Simulations using both actuator disk and actuator line models. Results suggest that when a wind turbine is yawed for the benefit of downstream turbines, the curled shape of the wake and its asymmetry must be taken into account since it affects how much of it intersects the downstream turbines.

Analytical Modeling of Wind Farms: A New Approach for Power Prediction

Abstract: Wind farm power production is known to be strongly affected by turbine wake effects. The purpose of this study is to develop and test a new analytical model for the prediction of wind turbine wakes and the associated power losses in wind farms. The new model is an extension of the one recently proposed by Bastankhah and Porte-Agel for the wake of stand-alone wind turbines. It satisfies the conservation of mass and momentum and assumes a self-similar Gaussian shape of the velocity deficit. The local wake growth rate is estimated based on the local streamwise turbulence intensity. Superposition of velocity deficits is used to model the interaction of the multiple wakes. Furthermore, the power production from the wind turbines is calculated using the power curve. The performance of the new analytical wind farm model is validated against power measurements and large-eddy simulation (LES) data from the Horns Rev wind farm for a wide range of wind directions, corresponding to a variety of full-wake and partial-wake conditions. A reasonable agreement is found between the proposed analytical model, LES data, and power measurements. Compared with a commonly used wind farm wake model, the new model shows a significant improvement in the prediction of wind farm power.

A Critical Review on Wind Turbine Power Curve Modelling Techniques and Their Applications in Wind Based Energy Systems

Abstract: Power curve of a wind turbine depicts the relationship between output power and hub height wind speed and is an important characteristic of the turbine. Power curve aids in energy assessment, warranty formulations, and performance monitoring of the turbines. With the growth of wind industry, turbines are being installed in diverse climatic conditions, onshore and offshore, and in complex terrains causing significant departure of these curves from the warranted values. Accurate models of power curves can play an important role in improving the performance of wind energy based systems. This paper presents a detailed review of different approaches for modelling of the wind turbine power curve. The methodology of modelling depends upon the purpose of modelling, availability of data, and the desired accuracy. The objectives of modelling, various issues involved therein, and the standard procedure for power performance measurement with its limitations have therefore been discussed here. Modelling methods described here use data from manufacturers’ specifications and actual data from the wind farms. Classification of modelling methods, various modelling techniques available in the literature, model evaluation criteria, and application of soft computing methods for modelling are then reviewed in detail. The drawbacks of the existing methods and future scope of research are also identified.

Estimating the wake deflection downstream of a wind turbine in different atmospheric stabilities: an LES study

Abstract: . An intentional yaw misalignment of wind turbines is currently discussed as one possibility to increase the overall energy yield of wind farms. The idea behind this control is to decrease wake losses of downstream turbines by altering the wake trajectory of the controlled upwind turbines. For an application of such an operational control, precise knowledge about the inflow wind conditions, the magnitude of wake deflection by a yawed turbine and the propagation of the wake is crucial. The dependency of the wake deflection on the ambient wind conditions as well as the uncertainty of its trajectory are not sufficiently covered in current wind farm control models. In this study we analyze multiple sources that contribute to the uncertainty of the estimation of the wake deflection downstream of yawed wind turbines in different ambient wind conditions. We find that the wake shapes and the magnitude of deflection differ in the three evaluated atmospheric boundary layers of neutral, stable and unstable thermal stability. Uncertainty in the wake deflection estimation increases for smaller temporal averaging intervals. We also consider the choice of the method to define the wake center as a source of uncertainty as it modifies the result. The variance of the wake deflection estimation increases with decreasing atmospheric stability. Control of the wake position in a highly convective environment is therefore not recommended.

Fault analysis of wind turbines in China

Abstract: The installed capacity of wind turbines in China increased rapidly in the past 10 years. Against the backdrop of growing wind turbine capacity, the failure of wind turbines is becoming increasingly serious. Based on the three primary configurations and failure statistics analysis of wind turbines in China, this paper summarizes the failures of wind turbine components, such as frequency converters, generators, gearboxes, pitch systems, yaw systems, blades, braking systems and sub-synchronous machines. Although there are many failure types and various causes, we can deduce four primary reasons for these failures: lack of core technologies; inferior quality due to price competition; design standards and wind farm climate differences; and no mandatory quality certification and exterior factors, such as wind farm construction, power grids and maintenance. Finally, while aiming to improve the reliability, a reliability management method with regard to the design, manufacturing and maintenance of wind turbines was proposed.

Progress and trends in nondestructive testing and evaluation for wind turbine composite blade

Abstract: Wind energy is one of the fastest growing renewable energy resources. It is distinctly important to increase reliability and availability of wind turbines and further to reduce the wind energy cost. Blades are considered to be one of the most critical components in wind turbine system because they convert Kinetic energy of wind into useable power. Blades are fabricated by carbon fiber reinforced polymer (CFRP) or glass fiber reinforced polymer (GFRP). Flaws and damages are inevitable during either fabrication or lifetime of a composite blade. Thus, non-destructive testing (NDT) and structural health monitoring (SHM) for wind turbine blade (WTB) are required to prevent failures and increase reliability in both manufacturing quality control and in-service inspection. In this work, a fully, in-depth and comprehensive review of NDT techniques for WTB inspection was reported based on an orderly and concise literature survey. Firstly, typical flaw and damage occurring in manufacturing progress and in service of WTB were introduced. Next, the developments of visual, sonic and ultrasonic, optical, electromagnetic, thermal and radiographic NDT for composite WTB inspection were reviewed. Thereafter, strengths and limitations of NDT techniques were concluded through comparison studies. In the end, some research trends in WTB NDT have been predicted, for example in combination with SHM. This work will provide a guide for NDT and SHM of WTB, which plays an important role in wind turbine safety control and wind energy cost savings. In addition, this work can benefit the NDT development in the field of renewable energy, such as solar energy, and energy conservation field, such as building diagnosis.

Performance parameters of Savonius type hydrokinetic turbine – A Review

Abstract: Energy crisis and high emission of fossil fuels are major driving forces for developing renewable energy based technologies. In order to meet growing demand for energy, hydropower can be one of the sustainable alternatives. Further, the hydrokinetic turbine is considered as one of the most emerging technologies which harness energy from flowing water. In this paper, an attempt has been made to review hydrokinetic energy theory for energy conversion system from water currents analogous to wind power system. The most widespread classes of hydrokinetic turbines are discussed in detail with respect to their benefits, drawbacks and desirable conditions for applications. It has been found that in spite of some prevailing downsides of vertical axis turbine like of self-starting and lower efficiency, vertical axis turbines are appealing for many riverine applications. One of the prominent turbines of its kind is the Savonius hydrokinetic turbine that has the capacity to self-start at a very low fluid velocity in the river, canal etc. However, Savonius type hydrokinetic turbine inherently has poor efficiency. A number of experimental and numerical studies with a large number of physical designs and parameters have been carried out in the area of Savonius rotor to enhance its efficiency. Under this study, review of different parameters affecting the performance of Savonius hydrokinetic turbine has been carried out and presented in this paper which may be useful for future studies to improve the efficiency of such turbines.

Design of a Unified Power Controller for Variable-Speed Fixed-Pitch Wind Energy Conversion System

Abstract: A unified power controller for variable-speed fixed-pitch wind energy conversion system (WECS) is designed covering the whole range of wind speed in this paper. The proposed controller is composed of a modified maximum power point tracking (MPPT) controller in low wind speed and a new constant speed and constant power controller in high wind speed. For the former, a combination of modified hill climb searching (HCS) and power signal feedback (PSF) MPPT algorithms is used. The modified HCS method is activated to search for the maximum power point (MPP) first, which is followed by the PSF method once one MPP is found. By using this controller, not only the a priori knowledge of the aerodynamic characteristics of turbine blades is avoided, but also low torque/power ripple is achieved; for the latter, a new auxiliary passive stall control method is proposed. It temporarily increases the output power to force the turbine to operate in deep stall regime, thus to decrease the captured power of the turbine. The proposed controller is implemented on a digital signal processor. The validity of the proposed method is verified by experimental results done on a 10-kW WECS.

Gas Turbine Performance

Abstract: Industrial gas turbines show performance characteristics that distinctly depend on ambient and operating conditions. They are not only influenced by site elevation, ambient temperature, and relative humidity, but also by the speed of the driven equipment, the fuel, and the load conditions. Proper application of gas turbines requires consideration of these factors. This tutorial explains these characteristics based on the performance of the engine compressor, the combustor and the turbine section, and certain control strategies. It introduces fundamental concepts that help to understand the flow of energy between the components. Additionally, methods are introduced that allow the use of data for trending and comparison purposes. The impact of component degradation on individual component performance, as well as overall engine performance is discussed, together with strategies to reduce the impact of degradation.

Current-Aided Order Tracking of Vibration Signals for Bearing Fault Diagnosis of Direct-Drive Wind Turbines

Abstract: Vibration monitoring is one of the most popular, effective, and reliable methods for bearing fault diagnosis. A key issue in the vibration monitoring for the bearings used in variable-speed wind turbines is the elimination of the effect of the turbine shaft speed fluctuation in the vibration signals measured under varying-rotating-speed conditions. This paper proposes a new current-aided vibration order tracking method for bearing fault diagnosis of variable-speed direct-drive (i.e., no gearbox) wind turbines. The method explores a new simple and effective approach to acquire the reference signal from a current signal measured from the stator of the generator for vibration order tracking. First, the instantaneous fundamental frequency of the current signal is estimated in the time-frequency domain to obtain the shaft rotating frequency. Then, the shaft phase-time relationship is established. With this information, the envelope of the synchronously recorded vibration signal is subsequently resampled at the equal-phase-increment time points. Finally, bearing fault diagnosis is performed by observing the peaks at bearing characteristic frequencies in the power spectrum of the resampled vibration envelope signal. The proposed method is validated by successful diagnosis of different bearing faults in a direct-drive wind turbine under varying-speed conditions.

Wind tunnel testing of wake control strategies

Abstract: Goal of this paper is to present results from wind tunnel tests aimed at evaluating the potential of different wake control strategies for wind farm power maximization and load reduction. The experiments are conducted in a large boundary layer wind tunnel, using up to six servo-actuated and highly sensorized wind turbine scaled models in different wind farm layouts. Two main strategies are considered: the first derates the upstream wind turbines, while the second aims at redirecting wakes away from the downstream machines. The latter strategy is implemented in two alternative ways, using either active yawing or individual blade pitching. The impact on wind farm power and loading of these control strategies is discussed, highlighting the most promising ones.