Individual Pitch Research Articles

Research on individual pitch control below rated wind speed

The structure of the modern wind turbine is becoming larger and more complex, with the wind rotor exceeding hundreds of meters in diameter. The blade shear force is also becoming increasingly serious below the rated wind speed, which leads to structure fatigue loads and instability of the generator power. For improving the dynamic performance of large wind turbines, it was proposed that individual pitch control (IPC) method was operated below the rated wind speed. In this paper, we analyze the relationship between the aerodynamic characteristics of blades and the nonlinear time‐varying pitch control system based on wind shear and the tower shadow effect. The combination of IPC and torque control is used to optimize the control mode of the wind turbine. By fine‐tuning the pitch angle, the unbalanced force on the wind rotor was relieved to achieve the purpose of mitigating fatigue loads. Finally, our experimental results prove the validity of the proposed IPC method below the rated wind speed by showing that it can improve power quality and reduce fatigue loads of the key components without reducing the generator output power. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Wind turbine blade optimisation with individual pitch and trailing edge flap control

Individual pitch control and trailing edge flaps have been shown to be capable of reducing flapwise fatigue loads on wind turbine blades, with research to date focusing on controller development and performance assessment. This work covers development of a blade optimisation process which integrates synthesis of individual pitch and trailing edge flap controllers to evaluate their impact on the levelised cost of energy. The optimisation process selects blade chord, twist and material distributions, along with the spar cap width, and integrates a turbine cost and mass model with existing simulation codes. Constraints based on ultimate stresses, fatigue damage, blade deflection, resonant frequency, and rotor thrust are considered. Using the NREL 5 MW reference turbine as an initial point, reductions in the levelised cost of energy of 1.05% are obtained with collective pitch control only, while the addition of individual pitch control increases this reduction to 1.17%. The use of trailing edge flaps on top of individual pitch control increases the reduction in the levelised cost of energy to 1.27%. Blade mass and material cost reductions from 13.6 to 16.4% and 18.1–21.5% respectively are also obtained. Optimised blade designs are driven by blade deflection, rotor thrust and ultimate stresses in the spar cap.

Economic analysis of Lidar-based proactively controlled wind turbines

This paper analyzes the financial feasibility and the investment attractiveness of a wind farm that uses a Lidar unit for proactive turbine controls. A thorough technical analysis is performed for evaluating the effectiveness of the Lidar for proactive blade pitch control. It is observed that using a Lidar for individual blade pitch control results in a significant reduction of the blade root damage equivalent loads. Furthermore, a pro-forma cashflow based economic tool is developed for modeling, comparing, and analyzing wind energy projects. This tool utilizes capital budgeting tools such as net present value, internal rate of return, equivalent annual annuity and payback period for analyzing investment attractiveness. Moreover, this paper utilizes wind conditions, costs and expenses, financing schemes, incentives, and operational strategies for analyzing wind projects with or without Lidars. The component fatigue load reduction achieved using Lidar based control can either be used to increase the useful life of the farm or to up-rate (repower) the turbine for the same operational life. This work analyzes the financial impacts of each of the aforementioned scenarios for a range of wind conditions. Also, the financial impact of PTC availability on a Lidar-assisted wind project has been analyzed in this research.

Investigation on pitch system loads by means of an integral multi body simulation approach

In modern horizontal axis wind turbines the rotor blades are adjusted by three individual pitch systems to control power output. The pitch system consists of either a hydraulic or an electrical actuator, the blade bearing, the rotor blade itself and the control. In case of an electrical drive a gearbox is used to transmit the high torques that are required for blade pitch angle adjustment. In this contribution a new integral multi body simulation approach is presented that enables detailed assessment of dynamic pitch system loads. The simulation results presented are compared and evaluated with measurement data of a 2 MW-class reference wind turbine. Major focus of this contribution is on the assessment of non linear tooth contact behaviour incorporating tooth backlash for the single gear stages and the impact on dynamic pitch system loads.

Comparison of Life Calculations for Oscillating Bearings Considering Individual Pitch Control in Wind Turbines

The fatigue life calculation of bearings under rotating conditions has been well researched and standardized. In contrast, for bearings in oscillating applications no international standards exist. As a result, pitch bearings in wind turbines are designed with different, non standardized approaches. Furthermore, the impact of individual pitch control on pitch bearings has not yet been studied. In this paper four approaches for fatigue life calculation will be applied and compared under individual pitch control conditions. For comparison, the loads and the bearing geometry of the reference turbine IWT 7.5 MW, which is individual pitch controlled, are used. This paper will show how the bearing life calculated by different approaches reacts to individual pitch control conditions. Furthermore, the factors for the modified rating life, according to the ABMA and ISO standards, which implement different operation conditions on the bearings in rotating applications, are calculated for the given loads and the given bearing geometry in oscillating applications.

On the functional design of the DTU10 MW wind turbine scale model of LIFES50+ project

This paper illustrates the mechatronic design of the wind tunnel scale model of the DTU 10MW reference wind turbine, for the LIFES50+ H2020 European project. This model was designed with the final goal of controlling the angle of attack of each blade by means of miniaturized servomotors, for implementing advanced individual pitch control (IPC) laws on a Floating Offshore Wind Turbine (FOWT) 1/75 scale model. Many design constraints were to be respected: among others, the rotor-nacelle overall mass due to aero-elastic scaling, the limited space of the nacelle, where to put three miniaturized servomotors and the main shaft one, with their own inverters/controllers, the slip rings for electrical rotary contacts, the highest stiffness as possible for the nacelle support and the blade-rotor connections, for ensuring the proper kinematic constraint, considering the first flapwise blade natural frequency, the performance of the servomotors to guarantee the wide frequency band due to frequency scale factors, etc. The design and technical solutions are herein presented and discussed, along with an overview of the building and verification process. Also a discussion about the goals achieved and constraints respected for the rigid wind turbine scale model (LIFES50+ deliverable D.3.1) and the further possible improvements for the IPC-aero-elastic scale model, which is being finalized at the time of this paper.

Iterative tuning of feedforward IPC for two-bladed wind turbines

At present, the cost of offshore wind energy does not meet the level of onshore wind and fossil-based energy sources. One way to extend the turbine lifetime, and thus reduce cost, is by reduction of the fatigue loads of blades and other turbine parts using Individual Pitch Control (IPC). This type of control, which is generally implemented by feedback control using the MultiBlade Coordinate transformation on blade load measurement signals, is capable of mitigating the most dominant periodic loads. The main goal of this article is to develop a self-optimizing feedforward IPC strategy for a two-bladed wind turbine to reduce actuator duty cycle and reduce the dependency on blade load measurement signals. The approach uses blade load measurement data only initially for tuning of the feedforward controller, which is scheduled on the rotor azimuth angle and wind speed. The feedforward strategy will be compared to the feedback implementation in terms of load alleviation capabilities and actuator duty cycle. Results show that the implementation is capable of learning the optimal feedforward IPC controller in constant and turbulent wind conditions, to alleviate the pitch actuator duty cycle, and to considerably reduce harmonic fatigue loads without the need for blade load measurement signals after tuning.

Controller design for wind turbine load reduction via multiobjective parameter synthesis

During the design process for a wind turbine load reduction controller many different, sometimes conflicting requirements must be fulfilled simultaneously. If the requirements can be expressed as mathematical criteria, such a design problem can be solved by a criterion-vector and multi-objective design optimization. The software environment MOPS (Multi-Objective Parameter Synthesis) supports the engineer for such a design optimization. In this paper MOPS is applied to design a multi-objective load reduction controller for the well-known DTU 10 MW reference wind turbine. A significant reduction in the fatigue criteria especially the blade damage can be reached by the use of an additional Individual Pitch Controller (IPC) and an additional tower damper. This reduction is reached as a trade-off with an increase of actuator load.

Tower Based Load Measurements for Individual Pitch Control and Tower Damping of Wind Turbines

The cost of IPC has hindered adoption outside of Europe despite significant loading advantages for large wind turbines. In this work we presented a method for applying individual pitch control (including for higher-harmonics) using tower-top strain gauge feedback instead of blade-root strain gauge feedback. Tower-top strain gauges offer hardware savings of approximately 50% in addition to the possibility of easier access for maintenance and installation and requiring a less specialised skill-set than that required for applying strain gauges to composite blade roots. A further advantage is the possibility of using the same tower-top sensor array for tower damping control. This method is made possible by including a second order IPC loop in addition to the tower damping loop to reduce the typically dominating 3P content in tower-top load measurements. High-fidelity Bladed simulations show that the resulting turbine spectral characteristics from tower-top feedback IPC and from the combination of tower-top IPC and damping loops largely match those of blade-root feedback IPC and nacelle- velocity feedback damping. Lifetime weighted fatigue analysis shows that the methods allows load reductions within 2.5% of traditional methods.

Lidar-Assisted Feedforward Individual Pitch Control to Compensate Wind Shear and Yawed Inflow

Lidar-assisted individual pitch control (IPC) has been investigated occasionally in recent years, focusing on the compensation of (vertical) wind shear as the main disturbance. Since yawed inflow might cause significant load fluctuations too, it is worth to compensate. Load patterns caused by yawed inflow significantly differ from those caused by wind shear, requiring a more sophisticated control algorithm. In this paper a lidar-assisted cyclic pitch feedforward control to compensate wind shear and yawed inflow is presented. The main objective is the analysis of the load patterns through a simplified aerodynamic model, which among other things focuses on a reasonable representation of the skewed wake effect. Establishing a suitable structure of the feedforward controller follows. The paper concludes with a comparison of fatigue load reductions achieved by three different controllers. Firstly, a well-known feedback individual pitch control; secondly, a feedforward controller for pure wind shear compensation and thirdly, this new feedforward controller to compensate wind shear and yawed inflow. The last two controllers use ideal lidar measurement chains.

On the optimal tuning of individual pitch control for horizontal-axis wind turbines

Individual pitch control has proved capable of reducing loads on the blades and shaft of a horizontal-axis wind turbine, at the price of a potentially substantial increase in actuator activity. With accurate tuning of the control parameters, the overall performance can be satisfactorily balanced, but a manual tuning procedure often proves unbearably costly and the solution found may be far from optimal. This study tries to explore the feasibility of an optimal approach to the problem of tuning of individual pitch control, by mapping reasonable cost functions with respect to some parameters of interest in control design. The analysis is carried out by considering a possible individual pitch control implementation, tested in a virtual environment on a realistic testbed. The merit functions are also analyzed visually, in order to easily understand the effects of the various design parameters on the positions and quality of the respective optima. In a later stage, results of complete optimization runs are presented, and the approach is critically discussed.

Effects of acoustic and linguistic experience on Japanese pitch accent processing

This study investigated the effects of L2 learning experience in relation to L1 background on hemispheric processing of Japanese pitch accent. Native Mandarin Chinese (tonal L1) and English (non-tonal L1) learners of Japanese were tested using dichotic listening. These listener groups were compared with those recruited in Wu, Tu & Wang (2012), including native Mandarin and English listeners without Japanese experience and native Japanese listeners. Results revealed an overall right-hemisphere preference across groups, suggesting acoustically oriented processing. Individual pitch accent patterns also revealed pattern-specific laterality differences, further reflecting acoustic-level processing. However, listener group differences indicated L1 effects, with the Chinese but not English listeners approximating the Japanese patterns. Furthermore, English learners but not naïve listeners exhibited a shift towards the native direction, revealing effects of L2 learning. These findings imply integrated effects of acoustic and linguistic aspects on Japanese pitch accent processing as a function of L1 and L2 experience.

Control design for a two-bladed downwind teeterless damped free-yaw wind turbine

In this paper, a control architecture for a two-bladed downwind teeterless damped free-yaw wind turbine is developed. The wind turbine features a physical yaw damper which provides damping to the yawing motion of the rotor-nacelle assembly. Individual Pitch Control (IPC)11List of abbreviations: Individual Pitch Control (IPC); Collective Pitch Control (CPC); Linear Individual Pitch Control (LIPC); Multi-Blade Coordinate (MBC); Multi-Blade Coordinate (MBC); Out-of-Plane (OoP); In-Plane (IP); Variance Accounted For (VAF); Damage Equivalent Load (DEL); Extreme Direction Change (EDC); Proportional Integral (PI).List of symbols: Ttrq: Demanded generator torque for speed regulation; Tdtd: Demanded generator torque for drivetrain damping; Tgen: Demanded generator torque; Ωrated: Rated generator speed setpoint; Ωgen: Generator speed control setpoint; θcol: Collective blade pitch angle; θcol: Collective blade pitch angle; θ1: Individual blade 1 pitch angle; θ2: Individual blade 2 pitch angle; Θ1: Blade 1 pitch angle; Θ2: Blade 2 pitch angle; θtilt: Non-rotating blade pitch setpoint for tilt coordinate; θyaw: Non-rotating blade pitch setpoint for yaw coordinate; My, 1: Blade 1 Out-of-Plane root bending moment; My, 2: Blade 2 Out-of-Plane root bending moment; Mx, 1: Blade 1 In-Plane root bending moment; Mx, 2: Blade 2 In-Plane root bending moment; Mtilt: Rotor tilt moment; Myaw: Rotor yaw moment; ψ: Rotor azimuth angle; ψoff: Azimuth angle offset; ϕref: Yaw setpoint angle; ϕ˙yb: Yaw bearing angular velocity; n: n’th harmonic of load; ϕyaw: Yaw misalignment (between turbine yaw position and wind direction); ϕ: Yaw error (controller input); Lθ: Low-pass filter for individual pitch angles; Lϕ: Low-pass filter for yaw misalignment signal; HIPC: High-pass filter for individual blade pitch signals; Lyb: Low-pass filter for yaw bearing angular velocity signal; fIPC: Cut-off frequency of high-pass filter for individual pitch control κ: Gain of yaw model; τ: Time constant of yaw model; Td: Time delay in yaw model. is employed to obtain yaw control so as to actively track the wind direction and to reduce the turbine loads. The objectives of both load and yaw control by IPC are conflicting and therefore two decoupling strategies are presented and compared in terms of controller design, stability, and turbine loads. The design of the different controllers and the physical yaw damping are coupled and have a large impact on the turbine loads. It is shown that the tuning of the controllers and the choice of the yaw damping value involve a tradeoff between blade and tower loads. All results have been obtained by high-fidelity simulations of the state-of-the-art 2-B Energy 2B6 wind turbine.

Blade pitch control of straight-bladed vertical axis wind turbine

Collective pitch control and individual pitch control algorithms were present for straight-bladed vertical axis wind turbine to improve the self-starting capacity. Comparative analysis of straight-bladed vertical axis wind turbine(SB-VAWT) with or without pitch control was conducted from the aspects of aerodynamic force, flow structure and power coefficient. The computational fluid dynamics (CFD) prediction results show a significant increase in power coefficient for SB-VAWT with pitch control. According to the aerodynamic forces and total torque coefficient obtained at various tip speed ratios (TSRs), the results indicate that the blade pitch method can increase the power output and decrease the deformation of blade; especially, the total torque coefficient of blade pitch control at TSR 1.5 is about 2.5 times larger than that of fixed pitch case. Furthermore, experiment was carried out to verify the feasibility of pitch control methods. The results show that the present collective pitch control and individual pitch control methods can improve the self-starting capacity of SB-VAWT, and the former is much better and its proper operating TSRs ranges from 0.4 to 0.6.

Individual pitch controller based on fuzzy logic control for wind turbine load mitigation

With the increasing size of modern large wind turbine (WT), the effects of dynamic loading on the structures become an important influence factor. There are mitigation measures for WT control systems to reduce these imbalance structural loads and regulate power. It has motivated the development of blade individual pitch control (IPC) methodologies. This study focuses on the design of fuzzy logic controller (FLC) for IPC. The controllers are designed in order to optimise a trade-off among several control objectives such as blade root moment and generator torque. Three different FLC had been used in the controllers, the first one related to blade pitch angle and electromagnetic torque control variables to meet specified objectives for operation region, the second control model and the third model related to d-q axis blade moment in non-rotating frame of reference. Likewise, the optimisation criteria of FLC consider for each controller objective to mitigate fatigue loads and regulate output power. Finally, the effectiveness of proposed method is verified by simulation results for three-bladed NREL 2 MW WT. The results proved that the fatigue loads in the turbine are reduced obviously.

Sensorless control of a power converter for a cluster of small wind turbines

This study presents a new sensorless control for small wind turbine clusters with a single power converter with a direct torque control algorithm. The proposed system consists of a wind farm connected to a back-to-back power converter that interfaces the wind farm with the AC grid. The studied wind turbines are based on fixed-speed wind turbines equipped with squirrel cage induction generators with individual pitch control. The presented structure permits to reduce the number of converters and allows to accomplish the grid codes (fault ride through capability and reactive power support). Furthermore, the generated active power can be reduced according to grid operator requirements. The presented control scheme can be applied to wind turbine repowering projects, wind farms connected to a microgrid, even, new small onshore and offshore power plants. The system performance and stability is studied and validated by means of dynamic simulations.

Vibration reduction strategy for wind turbine based on individual pitch control and torque damping control

This paper presents the vibration reduction strategy of large-size pitch-controlled variable-speed wind turbine based on pitch control and torque control. First, the torque control below the rated operating area and the pitch control above rated operating area are presented, and the control method to reduce the coupling between torque control and pitch control is discussed. Then the vibration mechanism and the modal analysis of the main components (the blade, tower and drive train) of wind turbine are studied. In terms of alleviating the blade flap-wise vibration and drive train torsion vibration, the individual pitch control strategy and torque damping control strategy are proposed to reduce the fluctuations of blade flap-wise load and add damping to the drive train torsion vibration mode. Finally, simulations were conducted using the GH Bladed 1.5-MW wind turbine, and the results show that the proposed vibration reduction strategy can effectively alleviate the blade flap-wise vibration and drive train torsion vibration. Besides, because of the coupling relationship of blade/tower/drive train vibration modes, the proposed strategy can also mitigate the tower fore-aft and side-side vibration. Copyright © 2016 John Wiley & Sons, Ltd.

Dysphonia Severity Index in Typically Developing Indian Children

Dysphonia is a variation in an individual's quality, pitch, or loudness from the voice characteristics typical of a speaker of similar age, gender, cultural background, and geographic location. Dysphonia Severity Index (DSI) is a recognized assessment tool based on a weighted combination of maximum phonation time, highest frequency, lowest intensity, and jitter (%) of an individual. Although dysphonia in adults is accurately evaluated using DSI, standard reference values for school-age children have not been studied. This study aims to document the DSI scores in typically developing children (8-12 years). A total of 42 typically developing children (8-12 years) without complaint of voice problem on the day of testing participated in the study. DSI was computed by substituting the raw scores of substituent parameters: maximum phonation time, highest frequency, lowest intensity, and jitter% using various modules of CSL 4500 software. The average DSI values obtained in children were 2.9 (1.23) and 3.8 (1.29) for males and females, respectively. DSI values are found to be significantly higher (P = 0.027) for females than those for males in Indian children. This could be attributed to the anatomical and behavioral differences among females and males. Further, pubertal changes set in earlier for females approximating an adult-like physiology, thereby leading to higher DSI values in them. The mean DSI value obtained for male and female Indian children can be used as a preliminary reference data against which the DSI values of school-age children with dysphonia can be compared.

An assessment of using variable blade pitch for moored ocean current turbine flight control

This paper investigates the possibility of using active individual blade pitch control for positioning moored ocean current turbines within an array. Using a numerical simulation of a representative ocean current turbine it is shown that harmonic blade oscillations with amplitudes of 1.5° can be used to displace an ocean current turbine laterally by a distance equal to one rotor diameter, when the mooring cable length is approximately 30 times the diameter of the rotor blade. For current flow directions that would result in a downstream turbine operating in the wake of an upstream system at a distance of 10 diameters, this technique could be used to reduce the power loss of the downstream system from about 50% (caused by the reduced flow speed available in the turbine wake) to the 1.2% power loss associated with the suggested control approach.

風力発電システムの独立翼ピッチ操作による翼荷重ゲインスケジューリング制御

A gain-scheduled control approach of blade loads using individual blade pitch manipulation is developed to reduce variations in aerodynamic loads of wind turbines during rotation. The motivation of the study is that the dynamic characteristics of the blade loads depend on the wind speed and blade pitch. The developed approach consists of the gain-scheduled feedback control (PI action) of the rotor speed using collective blade pitch and generator torque manipulations and the gain-scheduled feedback control (P action) of the d- and q-axis blade loads using individual blade pitch manipulation. The gain-scheduling strategy for the blade load control is developed through a numerical analysis of the NREL 5MW-onshore wind turbine-generator system using the aeroelastic simulation model (FAST) and the observed high wind speed data. The sensitive analysis of the proportional gain for the blade load control reveals that the stability limit gain decreases with the increase in the wind speed. The gain-scheduling strategy based on the stability limit gain reduces the variation in the blade loads during rotation as compared with the individual blade pitch manipulation using the fixed gain as well as the collective blade pitch manipulation without the blade load control.