Repetitive Individual Pitch Control for Load Alleviation at Variable Rotor Speed

This paper considers individual blade pitch (IBP) control for wind turbines and investigates its blade load mitigation performance under wind shear using a wind turbine scale model. We show through an experiment that IBP is effective in reducing the blade load while not deteriorating the rotor speed regulation performance.

Wind Turbine Trailing Edge Noise: Mitigation of Normal Amplitude Modulation by Individual Blade Pitch Control

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. Copyright © 2017 John Wiley & Sons, Ltd.

This study discusses the load mitigation of unbalanced wind turbines, including balanced and unbalanced loads. Regarding the wind turbine load reduction, it has been shown that individual pitch control (IPC) is more promising in comparison with collective pitch control. However, wind turbine unbalance will cause extra loads and fatigue on the wind turbine rotor, which has not been taken into consideration by the traditional IPC method. This study presents a new control strategy to mitigate the loads of the unbalance wind turbines. An IPC scheme consisting of a proportional–integral (PI) controller and two resonant (R) compensators is presented. The PI‐R regulator is implemented in the hub reference frame to reduce both the balanced and unbalanced loads of the turbine. The wind turbine code FAST (fatigue, aerodynamics, structures and turbulence) is used for the wind turbine load modelling. The simulations are conducted on the NREL upwind 1.5 MW wind turbine model. Elimination of both the balanced and unbalanced loads of the wind turbine has been achieved, so that PI‐R IPC is demonstrated as an effective means for load mitigation of unbalanced wind turbines.

This paper presents the preliminary study on damping of platform pitch motion of floating offshore wind turbine using adaptive individual blade pitch control. The platform pitch displacement is measured and used to derive the signal to actuate pitch of each blade independently which tries to damp the platform pitch motion. This independent blade pitch control signal is then combined with collective blade pitch control signal which is responsible for regulating the generator speed. The performance of proposed controller is compared with the baseline PID collective pitch controller and adaptive collective pitch controller.

To minimize the levelized cost of energy (LCOE) of wind turbines, advanced co-design strategies are required that also consider the contribution of active blade pitch control to overall energy production and wind turbine cost. Thereby, the demanded closed-loop performance drives the requirements on the blade pitch actuation system, which needs to be carefully balanced. To enable this, an extended LCOE measure is developed in this paper using stochastic estimates for quantifying pitch actuation cost in terms of pitch power and closed-loop performance in terms of net energy production. Additionally, the impact of blade pitch deflections on structural loads and hence cost is evaluated considering both collective and individual pitch control. The interdependencies between the different design objectives are revealed in a case study carried out on a 25MW wind turbine, demonstrating the guidance for engineers toward cost-effective and efficient wind turbine designs.

Multi-rate model predictive control to reject periodic disturbance with reduced ripple

This article reviews the design of algorithms for individual pitch control in the case of variable speed turbines. The aim of the designed control algorithm is to improve the power quality and to reduce voltage flicker. A simulation model of variable speed wind turbine was developed with the simulation tool of PSCAD/EMTDC. This article compared the individual pitch action and the collective pitch action, which is the same for all three blades, is calculated by means of a standard classical PI-based controller. The simulation result indicates that compared with the flicker coefficient of PI controlled wind turbine, the variable-speed wind turbines equipped with individual pitch controller, exhibit good behavior with respect to output power and voltage flicker, especially for 3P frequency reduction. Thereby, the variable-speed wind turbine with individual pitch controller will produce lower voltage flicker.

Repetitive model predictive control applied to a simulated moving bed chromatography system

The premise of collective pitch control is that wind speed is the same in the rotor plane, but wind shear and tower shadow makes wind speed in the rotor rotating plane changing differently. It affects the corrective pitch control greatly and increases the fatigue load. This paper model 1.5MW doubly-fed WTG (wind turbine generator) for individual pitch control, and analyze the main reason of periodic load fluctuation. Then individual pitch control based on blade element theory was researched combining the actual of the load is difficult to measure. Pitch angle was distributed by weight coefficient to realize individual pitch control. The weight coefficient was computed according to the wind speed with consideration of trailing vortex, wind shear and tower shadow. Simulations indicate that the proposed individual pitch control method not only meet the basic power control request but also reduce fluctuation of load, so it can solve the problem of fatigue load and prolong the lifetime in process of development to large-scale WTG.

The Unix operating system: K Christian John Wiley, New York, NY, USA (1988) 455 pp £25.95 hardback £17.50 softback (2nd edition)

Individual/collective blade pitch control of floating wind turbine based on adaptive second order sliding mode

Momentum theory model which was widely used in pitch control cant calculate wind turbine load, so it can't meet pitch control research needs of large-scale wind turbine. In this paper, the traditional model based on momentum theory firstly was improved to be able to calculate load under some hypothesis. Then the wind turbine model suitable for individual pitch control was built based on blade element theory. And wind shear and tower shadow on load of wind turbine was calculated and analyzed. Finally, the model was simulated in the turbulent flow conditions and load was analyzed by Bladed. Simulations indicate that the model built in the paper can be used in simulation and verification of individual pitch control, and the conclusions drawn by load analysis can provide theoretic basis and the reference standard for individual pitch control strategy.

Fundamental study on aerodynamic force of floating offshore wind turbine with cyclic pitch mechanism

The main objective of wind turbine control is to make wind power production economically more efficient. This objective is often achieved in two distinct regions, i.e., the below rated wind speed and the above rated wind speed regions. In the below rated wind speed region, generator torque control is used primarily to control rotor speed to track the maximum power coefficient in order to maximize energy capture. In the above rated wind speed region, the blade pitch control is used primarily to regulate the rotor speed in order to regulate the aerodynamic power within its design limit [1]. As the wind turbine sizes are increasing and their mechanical components are built lighter, the reduction of the structural loads becomes a very important task of wind turbine control because structural loads can reduce turbine reliability and lifespan and also may cause power fluctuations. In particular, the reduction of blade loads has received special interest. Wind speed variations across the turbine rotor during rotor rotation, which is caused by the large rotor blade size, the wind shear, turbulence and tower shadow effects, cause periodic oscillations in blade structural loads, andthis structural load is especially important in the above rated wind speed region because high structural loads arise from strong winds. Therefore the individual pitch control is sometimes considered since common collective pitch control cannot compensate for the periodic loads on the blades.