Individual Pitch Research Articles

Visually induced gains in pitch discrimination: Linking audio-visual processing with auditory abilities.

Perception is fundamentally a multisensory experience. The principle of inverse effectiveness (PoIE) states how the multisensory gain is maximal when responses to the unisensory constituents of the stimuli are weak. It is one of the basic principles underlying multisensory processing of spatiotemporally corresponding crossmodal stimuli that are well established at behavioral as well as neural levels. It is not yet clear, however, how modality-specific stimulus features influence discrimination of subtle changes in a crossmodally corresponding feature belonging to another modality. Here, we tested the hypothesis that reliance on visual cues to pitch discrimination follow the PoIE at the interindividual level (i.e., varies with varying levels of auditory-only pitch discrimination abilities). Using an oddball pitch discrimination task, we measured the effect of varying visually perceived vertical position in participants exhibiting a wide range of pitch discrimination abilities (i.e., musicians and nonmusicians). Visual cues significantly enhanced pitch discrimination as measured by the sensitivity index d', and more so in the crossmodally congruent than incongruent condition. The magnitude of gain caused by compatible visual cues was associated with individual pitch discrimination thresholds, as predicted by the PoIE. This was not the case for the magnitude of the congruence effect, which was unrelated to individual pitch discrimination thresholds, indicating that the pitch-height association is robust to variations in auditory skills. Our findings shed light on individual differences in multisensory processing by suggesting that relevant multisensory information that crucially aids some perceivers' performance may be of less importance to others, depending on their unisensory abilities.

Implementation of internal model based control and individual pitch control to reduce fatigue loads and tower vibrations in wind turbines

Vibration control and fatigue loads reduction are important issues in large-scale wind turbines. Identifying the vibration frequencies and tuning dampers and controllers at these frequencies are major concerns in many control methods. In this paper, an internal model control (IMC) method with an adaptive algorithm is implemented to first identify the vibration frequency of the wind turbine tower and then to cancel the vibration signal. Standard individual pitch control (IPC) is also implemented to compare the performance of the controllers in term of fatigue loads reduction. Finally, the performance of the system when both controllers are implemented together is evaluated. Simulation results demonstrate that using only IMC or IPC alone has advantages and can reduce fatigue loads on specific components. IMC can identify and suppress tower vibrations in both fore-aft and side-to-side directions, whereas, IPC can reduce fatigue loads on blades, shaft and yaw bearings. When both IMC and IPC are implemented together, the advantages of both controllers can be used. The aforementioned analysis and comparisons were not studied in literature and this study fills this gap. FAST, AreoDyn and Simulink are used to simulate the mechanical, aerodynamic and electrical aspects of wind turbine.

Fault-Tolerant Individual Pitch Control of a Wind Turbine with Actuator Faults

The sizes of wind turbines have been steadily increasing over the past decade, especially on the offshore sites. The greater structural flexibility of such machines necessitates considerations of reliable load mitigation techniques in order to alleviate the effects of asymmetric wind loads and fatigue. This paper proposes a reliable load mitigation scheme, referred to as ‘fault-tolerant individual pitch control’, which involves adjustments in pitch angles of the wind turbine blades individually in the presence of blade pitch actuator faults. The proposed scheme consists of a collective pitch control augmented with an individual pitch control, and a fault detection and diagnosis system. Simulation results obtained for a large-scale offshore wind turbine with a stochastic wind field illustrate effectiveness as well as fault-tolerance of the proposed scheme compared to the scheme based on control of pitch angles collectively. Moreover, the proposed scheme not only ensures more uniform output power with reduced loads on the turbine, but also tolerates the effects of possible faults in pith actuators of the blades.

Fault-tolerant Individual Pitch Control using Adaptive Sliding Mode Observer

Due to the increasing size of wind turbines, the unbalanced loads caused by the uneven spatial distribution of wind speed and turbulence are becoming larger and larger. As has been proved, individual pitch control (IPC) can mitigate the blade asymmetric loads greatly in region 3. On the other hand, the pitch actuator faults can affect the pitching performance with slow dynamics, resulting in generator power instability and even deteriorating the unbalanced loads of blades. However, the effects of unbalanced blade loads deterioration caused by pitch actuator faults have not been taken into account by the traditional IPC design. In the present paper, a fault-tolerant control (FTC) strategy using adaptive sliding mode estimation is combined with a traditional IPC system based on two different control methods (Proportional-Integral and H∞ loop-shaping). It maintains the nominal pitch performance and removes the negative effects of pitch actuator faults on generator power and unbalanced blade loads perfectly. The effectiveness of the proposed strategy is verified on the 5MW NREL wind turbine system.

Asymmetric Load Control Method for Individual Pitch of Horizontal Axis Marine Current Turbine

Asymmetric Load Control Method for Individual Pitch of Horizontal Axis Marine Current Turbine

Integrated Pitch Control System Design of a Wind Turbine by Using Multiobjective Optimization

Abstract The integrated pitch control system of a three-bladed, variable-speed, horizontal-axis large-sized wind turbines consists of three coupled control loops. The first one is known as collective pitch control (CPC). The second one is the active tower damping control (ATDC), which is used to damp tower oscillation due to the pitching activity. Finally, the third one is the individual pitch control (IPC), which is used to mitigate loads on the blades. In the present work, the coupled controllers are jointly tuned by using multiobjective optimization. Simulation results show that the proposed tuning approach yields satisfactory performance for all control loops.

Optimization and control of offshore wind farms with energy storage systems

This paper studies the optimal control strategies of hybrid renewable energy systems, focusing on offshore wind farms with energy storage systems (ESS), considering challenges of economic costs, operational reliability, and environmental impacts. Wind energy is widely exploited as a promising renewable energy source worldwide. The development of offshore wind farms (OWF) is emerging to utilize wind energy on a large scale, but face more complicated operational conditions and higher costs. A systematic methodology is proposed to optimize the costs of an OWF with ESS based on a framework that extends from the supervisory level dispatch strategies to individual pitch control for load reduction and fatigue mitigation. This holistic approach is able to improve the efficiency and economic performance of a wind farm through overall system optimization, while explicitly operating each wind turbine using a formally designed control framework leading to an extension of their service lifespan. This work provides novel solutions of wind energy and storage components deployment and has strong application potential.

Flexure pitch bearing concept for individual pitch control of wind turbines

AbstractThe excessive use of individual pitch control (IPC) for fatigue load reduction is accompanied by the uncertainty of potential bearing failures. This problem, which is due to the small swivel angles associated with IPC, arises because of the rolling and sliding contacts that occur with the rolling element bearings that are typically used. The use of a flexure bearing is proposed as a way of bypassing this issue. The flexure bearing enables a certain range of motion to be exclusively provided by elastic deformation. This article presents a novel bearing concept that is based on the hypothesis that such a flexure bearing can handle the unfavorable load conditions associated with IPC better than a rolling element bearing. Methods for the dimensioning of the aforementioned flexure bearing are therefore presented. The loads, particularly the required elastic rotation angle of the flexure bearing, are determined first. A promising design for the flexure bearing itself is then chosen and adapted to meet the specific requirements of IPC. These methods are applied to develop an initial conceptual design of the novel bearing unit for a 3‐bladed wind turbine of about 3.6 MW. The result demonstrates the feasibility of the concept, and a final discussion presents further opportunities of the design that will make this concept satisfy the special requirements of IPC.

Individual pitch control for 2‐bladed wind turbines via multiblade multilag transformation

AbstractTwo‐bladed wind turbines have regained the attention of the community thanks to the advantages in manufacturing cost provided by the lower number of blades and the ease of implementation of effective passive systems for load reduction (ie, teetering pin). Considering both teetering and nonteetering architectures, the dynamics of 2‐bladed turbines is different from that of 3‐bladed machines especially in terms of how multiples of the rotor frequencies in blade signals are translated on the fixed system. Such characteristics have hampered the adoption of active control laws for load mitigation based on individual pitch control, extensively studied for 3‐bladed turbines. A basic element for control development allowing to capture the essence of the relationship between signals on the blades and the fixed system on 2‐bladed turbines–represented by the Coleman transformation for 3‐bladed turbines–has not been identified yet. The present paper tries to fill the gap, presenting an extended transformation–called multiblade multilag–applicable to turbines with an arbitrary number of blades, providing a systematic way to link rotor signals to fixed system signals, thus allowing the application of control algorithms for individual pitch control developed for 3‐bladed turbines to the 2‐bladed case. The paper addresses the problem first at a theoretical level, and subsequently providing applicative results from simulations on virtual models of teetering and nonteetering 2‐bladed turbines. The proposed transformation algorithm and control laws allow to effectively reduce some relevant loads and motions respectively in the nonteetering and teetering scenarios, through a cyclic pitch input.

A reference open data vertical axis wind turbine, with individual pitch control, for code validation purposes

This paper presents the features and capabilities of a vertical axis wind turbine (VAWT) designed and built by the authors, which is meant to be the reference machine for open data code validation purposes under the project VODCA, VAWT Open Data for Code Assessment. The machine, whose design details are provided openly and summarized in the present document, has Individual Pitch Control (IPC) capability and it will be used for wind tunnel tests. Related results will be shared with participants who want to validate their own code, in terms of prediction of the aerodynamics or assessment of IPC strategies. The article reports a comprehensive overview of the state of the art of laboratory tests for VAWTs as well as the motivation of VODCA project, further to the need of code validation against experimental tests in controlled environment. The various phases of the project are also presented. Furthermore, the design of the carbon fiber blades, the structural components, as well as the mechatronics of the machine are summarized in this paper. Moreover, the experimental characterization of the machine's effective capabilities and properties, carried out after the completion of the building process, is reported and then the testing possibilities are defined and discussed.

A New Decentralized Pitch Control Scheme for Wind Turbines

Wind turbine rotor imbalances may be created by a multitude of causes, e.g. pitch misalignment, blade erosion. In such situations, machines experience undesired vibrations, which cannot be compensated or mitigated by the controllers generally adopted by industry today. This happens because the control action may be collective or both collective and cyclic, but, in order to cope with imbalances, it is necessary to employ a fully individual control which allows a blade to move independently from the others.In this paper we present a new individual pitch control algorithm able to simultaneously target the imbalance and reduce oscillating loads at frequencies multiple of the rotor revolution. The effectiveness of the proposed control is demonstrated in a high-fidelity simulation environment.

Load reduction on a clipper liberty wind turbine with linear parameter‐varying individual blade pitch control

AbstractThe increasing size of modern wind turbines also increases the structural loads caused by effects such as turbulence or asymmetries in the inflowing wind field. Consequently, the use of advanced control algorithms for active load reduction has become a relevant part of current wind turbine control systems. In this paper, an individual blade pitch control law is designed using multivariable linear parameter‐varying control techniques. It reduces the structural loads both on the rotating and non‐rotating parts of the turbine. Classical individual blade pitch control strategies rely on single‐control loops with low bandwidth. The proposed approach makes it possible to use a higher bandwidth since it accounts for coupling at higher frequencies. A controller is designed for the utility‐scale 2.5 MW Liberty research turbine operated by the University of Minnesota. Stability and performance are verified using the high‐fidelity nonlinear simulation and baseline controllers that were directly obtained from the manufacturer. Copyright © 2017 John Wiley & Sons, Ltd.

Scale model technology for floating offshore wind turbines

This study illustrates the aerodynamic and mechatronic design of a 1/75 scaled model of the DTU 10 MW wind turbine to perform wind tunnel tests in floating offshore configuration. Due to the strong discrepancy of the Reynolds number between full and model scale (up to 150), a dedicated low-Reynolds airfoil (SD7032) was chosen for the aerodynamic design of the blades, and the final shape was defined based on a dedicated optimisation algorithm which had as target the matching of the scaled thrust force and the first flap-wise bending frequency, as it is thoroughly explained in the study. Furthermore, the mechatronic design is reported in terms of the design choices adopted to get the best target-oriented functionalities to the model (i.e. individual pitch control, bandwidth) and to reduce as much as possible the weights, greatly affecting the aero-elastic scaling. The results gathered during experimental campaigns at Politecnico di Milano wind tunnel, are reported confirming the validity of the design and manufacturing choices.

A new fuzzy logic proportional controller approach applied to individual pitch angle for wind turbine load mitigation

In the world, efforts to increase the resource diversity in electric generation have accelerated lately. So, the great improvements have been achieved in wind turbines (WTs). The dimensions of WTs have grown for more electric generation and their energy productions have increased. Depending on these developments, it has become more important to reduce the WT load mitigation. Thus, a tendency to pass an individual pitch angle system control rather than a collective pitch angle system control employed to stable the output power of WTs over nominal wind speeds has whetted in recent studies. However, in literature, a controller proposal relating to how to incorporate the blade moments used for providing the individual pitch angle system into the output power control system has not yet been offered. Therefore, in this study, a new fuzzy logic proportional control (FL-P-C) approach has been recommended to mitigate the moment load on blades and tower to a minimum possible value while keeping the output power of WTs at a constant value. The offered FL-P-C has also been verified by MATLAB/Simulink. Through the first application of the FL-P-C on a WT, a significant improvement of 33–83% has been managed for the blade and tower moment loads. Furthermore, the grid fluctuations have been reduced because of the stabilisation of the output power of the WT. Ultimately, by the offered FL-P-C, not only the WT load mitigations and maintenance costs of WTs could be reduced, but also electric costs could be decreased owing to increasing lifetimes of WTs.

Dynamic aeroelastic behavior of wind turbine rotors in rapid pitch-control actions

Pitch control comprises a significant proportion of current wind turbine load-control approaches. Collective pitching is used in restricting the overall power generation at high winds, whereas individual pitching has the added advantage of mitigating cyclic loads that are detrimental in fatigue damage of the turbines. Currently, there are many studies on conventional pitching control that account for long-term variations in wind speeds and associated high loads, but a smaller number of studies in short-term pitch action.The present study focuses on the use of rapid pitch control for handling short-term variations in wind conditions and load fluctuations within one cycle of rotation, with special attention to the prognosis of the aeroelastic response of the rotor. We use a numerical model capable of handling the complexities of the multi-physics dynamics of a wind turbine rotor. Based on a nonlinear adaptive ODE algorithm, it provides a natural way to integrate the various multi-physics aspects of wind turbine dynamics, including the control system and the coupled response of the aerodynamics and the structural deformations of the rotor. Results are presented for the case study of the NREL-5MW Reference Wind Turbine, and their significance for wind-turbine rotors in general is discussed.

Study on Optimization of Control Mechanism in Vertical Axis Wind Turbine

Objective-This paper describes an attempt to streamline the execution of the Vertical Axis Wind Turbines (VAWT) utilizing dynamic sharp edge pitch control. Methods/analysis- Aerodynamic model is chosen based on the surface profile and NACA 4-digit series was found to be the most suitable category under which NACA 0018 aerofoil design parameters have been chosen for the VAWT blade design, based on the previous research. The outline of wind turbine picked here is an H-sort Darrieus VAWT which deals with the lift drive of the wind. Findings- Active Pitch controlled VAWT with individual pitch control of each blade along with vertical roller bearings in the system is done to obtainmaximum coefficient of power harnessed from the wind turbine setup and increase the efficiency by 12.5%. Applications: The proposed design system is suitable for low wind speed areas which turbine is installed at lower heights.

MODEL-BASED CONTROL OF UTILITY-SCALE WIND TURBINES

As wind turbine size increases, small increases in efficiency can lead to significant monetary and lifespan improvements. As utility scale wind turbines approach structural efficiency limits, control systems have become the primary means of improving power efficiency and reducing fatigue. In variable speed turbines, collective or individual blade pitch control is one of the most common control schemes for above-rated speed operation. This paper presents the design and implementation of a model-based controller for jointly controlling the wind turbines power and blade loading reduction. First, a high-fidelity simulation model of a 3MW wind turbine is devel-oped followed by the control development using a computationally efficient version of model predictive control which benefits from short-term wind speed forecasts. The proposed controller is com-prehensively tested under multiple practical scenarios and compared with conventional wind turbine control methods.

Individual pitch control on wind turbines with permanent magnet synchronous generator for reduction of mechanical load and stability of output power

Individual pitch control on wind turbines with permanent magnet synchronous generator for reduction of mechanical load and stability of output power

Optimal tuning of multivariable disturbance‐observer‐based control for flicker mitigation using individual pitch control of wind turbine

Multivariable disturbance accommodated observer based control (DOBC) scheme is presented to mitigate loads generated due to wind shear and tower shadow using individual blade pitch for above-rated wind speed condition of wind turbine. Wind shear and tower shadow add flickers as 1p, 3p, 6p and so on, (p is the rotor rotational frequency) for three-bladed wind turbine. Novel DOBC with individual pitch control (IPC) to mitigate the flickers is presented and linear state-space model of wind turbine with tower dynamics is developed. The proposed controller is tuned using optimal control theory to reduce fatigue of drive-train, tower and to regulate output power. The authors have tested the controller on NREL's 5 MW wind turbine, FAST (fatigue, aerodynamics, structures and turbulence) code is used for load modelling and MATLAB/Simulink is used for the simulation. A comparison of power spectral density of generator speed, drive-train torsion and tower fore-aft moment shows better mitigation to the flickers by proposed controller as compared with proportional–integral (PI) and disturbance accommodation control (DAC) with collective pitch control. Furthermore, it shows less degradation in the performance as moving away from the operating point for above-rated wind speed condition of wind turbine. It is concluded that proposed multivariable controller shows better mitigation to turbulent and cyclic aerodynamic loads, provide better regulation to output power using IPC of wind turbine and increased the lifetime of drive-train torsion and tower as compared with PI and DAC.

Correlation between the frequency difference limen and an index based on principal component analysis of the frequency-following response of normal hearing listeners

Subcortical phase locking tends to reflect performance differences in tasks related to pitch perception across different types of populations. Enhancement or attenuation in its strength may correspond to population excellence or deficiency in pitch perception. However, it is still unclear whether differences in perceptual capability among individuals with normal hearing can be predicted by subcortical phase locking. In this study, we examined the brain-behavior relationship between frequency-following responses (FFRs) evoked by pure/sweeping tones and frequency difference limens (FDLs). FFRs are considered to reflect subcortical phase locking, and FDLs are a psychophysical measure of behavioral performance in pitch discrimination. Traditional measures of FFR strength were found to be poorly correlated with FDL. Here, we introduced principal component analysis into FFR analysis and extracted an FFR component that was correlated with individual pitch discrimination. The absolute value of the score of this FFR principal component (but not the original score) was negatively correlated with FDL, regardless of stimulus type. The topographic distribution of this component was relatively constant across individuals and across stimulus types, and the inferior colliculus was identified as its origin. The findings suggest that subcortical phase locking at certain but not all FFR generators carries the neural information required for the prediction of individual pitch perception among humans with normal hearing.