Robust Control Design for Load Reduction on a Liberty Wind Turbine

Ossmann, Daniel; Theis, Julian; Seiler, Peter

doi:10.1115/dscc2016-9719

Cited by 6 publications

(4 citation statements)

References 11 publications

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“…Note that the design point of 12 m s −1 was chosen in Ossmann et al . as it provided the highest worst case margins compared with other design wind speeds. Compared with the LPV controller, the

H_{\infty}

controller achieves greater robustness for its specific design condition at 12 m s −1 , but the margins degrade with higher wind speeds.…”

Section: Verificationmentioning

confidence: 96%

“…The classical phase margin is around 70° at minimum showing a very robust behavior. To illustrate the main motivation of the LPV controller, the margins are compared with those achieved with a previous LTI design in Ossmann et al . In that paper, an

H_{\infty}

controller was designed for a fixed wind speed of 12 m s −1 with the same specifications as the LPV controller.…”

Section: Verificationmentioning

confidence: 99%

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

2017

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The 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. pitch control algorithm should not change the thrust and the torque of the turbine in order to maintain the power output at its desired level.Sophisticated, model-based state space control approaches also became possible by transforming the whole periodic system into the non-rotating frame. 7 Multivariable control designs were investigated in Bossanyi 2 on the basis of a linear quadratic regulator and in Geyler and Caselitz 8 and Vali et al. 9 on the basis of H 1 -norm optimal control. Adaptive control techniques for individual blade pitch control are presented in Magar et al. 10 Periodic control for load reduction using individual blade-pitch control was developed and tested in Stol et al. 11 These controllers aimed at the once-per-revolution (1P) blade loads and were shown to yield similar results as the classical two-SISO-loops control strategy. A direct extension of this control strategy to target loads at higher frequencies is addressed in van Engelen 12 and Petrović et al. 13 additionally using complex, higher-order transformations of the sensor data. Successful field test results of such controllers for two-bladed and three-bladed turbines is presented in Bossanyi et al. 14 However, in this case, a linear analysis of the closed-loop model to verify robustness and performance is not straightforward anymore. Further, it also requires several design steps instead of a single one. This is also true for the feedforward filters added in each of the two SISO loops to cope with the 3P loads on the nacelle proposed in Bossanyi. 15 The feedforward filters are designed using a constrained numerical optimizations technique. Because of these reasons, the classical two-SISO-loops control strategy serves for comparison in this paper. The reduction of higher frequency loads was also achieved in Barlas et al. 16 and Unguran and Kühn 17 by employing additional trailing edge flaps and in Larsen et al. 18 by using additional flow measurement sensors. The disturbance accommodation techniques that are presented in W...

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H_{\infty}

controller achieves greater robustness for its specific design condition at 12 m s −1 , but the margins degrade with higher wind speeds.…”

Section: Verificationmentioning

confidence: 96%

H_{\infty}

controller was designed for a fixed wind speed of 12 m s −1 with the same specifications as the LPV controller.…”

Section: Verificationmentioning

confidence: 99%

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

2017

Self Cite

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“…28,29 Ossmann et al design a multivariable linear parameter-varying full-order H ∞ -synthesized controller to attenuate 0P and 3P loads in the non-rotating frame, and they verify it on a real 2.5 MW wind turbine. 30,31,32 Geyler and Caselitz design two independent, full-order H ∞ -synthesized controllers to a) regulate the rotor speed and active damping of axial tower top oscillations with collective pitch control and b) to suppress the 0P loads induced by blade root bending moments with IPC, and they verify the controller on a 1.5 MW turbine model. 26 Lu et al present a H ∞ -synthesized controller in which a simplified, rigid-blade, blade-decoupled plant is pre-compensated with the series combination of a PI controller and 3P inverse notch filter to attenuate 0P and 3P loads.…”

Section: βNormmentioning

confidence: 99%

Investigation of H∞ -Tuned Individual Pitch Control for Wind Turbines

Henry,

Pusch,

Pao

2024

Preprint

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Large wind turbines experience amplified asymmetrical loads at particular harmonics of the rotational frequency. Individual pitch control (IPC) has emerged as a potential controls solution to this problem. H ∞ control, which facilitates robust, multivariable controller synthesis in the frequency domain, is a candidate approach to IPC design for several reasons. Firstly, the objectives of asymmetrical load attenuation are best described in the frequency domain. Secondly, the IPC control signals and loads in orthogonal directions are coupled, which necessitates a multivariable controller approach. Thirdly, H ∞ synthesis is a method that can explicitly impose constraints on the robustness of the closed-loop system. A downside of IPC is the significant increase in blade-pitch travel incurred, which introduces additional loading on the blade-pitch bearings over time. We investigate strategies to constrain the blade-pitch travel in the controller tuning procedure. A comprehensive study is thus presented for a range of H ∞ -synthesized IPCs to attenuate asymmetrical loads on large rotors at harmonics of the rotational frequency while mitigating blade-pitch travel. All developed controllers are validated and compared using a 25 MW fixed-bottom offshore wind turbine model via linear analysis of the robustness of the closed-loop system to input and output disturbances and nonlinear analysis via the study of structural load power spectra, damage-equivalent loads (DEL), and the actuator duty cycle (ADC) of the blade-pitch actuator.

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“…As the turbine size grows and the structural dynamics become more flexible, considerations on load reduction are more critical. () Therefore, extra control loops were proposed to reduce the structural loads, such as individual pitch control() and tower and drive train dampers. () These methods significantly decreased the loads but lead more complicated control structures.…”

Section: Introductionmentioning

confidence: 99%

Gridded‐based LPV control of a Clipper Liberty wind turbine

Shu

Seiler

2018

Wind Energy

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This paper proposes a linear parameter varying (LPV) control design for a Clipper Liberty C96 2.5 MW wind turbine to operate in all wind conditions. A standard approach is to use multiple single-input, single-output loops for control objectives at different wind speeds. This LPV controller instead takes these objectives into a uniformed multi-input, multi-output design framework. The key difference is that the LPV controller is specifically designed to smoothly transition from Region 2 to Region 3 operation. Reducing structural loads is another major concern in the design. Synthesis of the controller relies on a gridded-based LPV model of the turbine, which is constructed by interpolation of linearized turbine models at different wind speeds. To overcome the conservativeness in the design, parameter varying rates will be considered based on turbulent wind conditions. The performance of the LPV controller is evaluated using a high fidelity FAST model provided by Clipper. The LPV controller is directly compared with the baseline controller currently operating on the turbine. Simulations and analysis show that the LPV controller meets all performance objectives and has better load reduction performance.

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Robust Control Design for Load Reduction on a Liberty Wind Turbine

Cited by 6 publications

References 11 publications

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

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

Investigation of H∞ -Tuned Individual Pitch Control for Wind Turbines

Gridded‐based LPV control of a Clipper Liberty wind turbine

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