Pitch Control Law Research Articles

A fault detection method for pitch actuators faults in wind turbines

The paper presents a model-based fault detection method for pitch actuators faults using the normalized gradient method to estimate the parameters of the pitch actuator. One major difficulty is that the input signal to the parametric estimation method must be a persistent excitation. To circumvent this, a chattering term is added to the pitch control law and the usual low-pass filters are not used for the parametrization in the normalized gradient method (thus acceleration information is used). In order to verify the proposed method, simulations are conducted within a Hardware in the Loop (HiL) platform using the wind turbine simulation software FAST (Fatigue, Aerodynamics, Structures, and Turbulence).

A Composite Super-Twisting Sliding Mode Approach for Platform Motion Suppression and Power Regulation of Floating Offshore Wind Turbine

The floating platform motion of an offshore wind turbine system can exacerbate output power fluctuations and increase fatigue loads. This paper proposes a new scheme based on a fast second-order sliding mode (SOSM) control and an adaptive super-twisting extended state observer to suppress the platform motion and power fluctuation. Firstly, an affine nonlinear model of the floating wind turbine pitch system is constructed. Then, a fast SOSM pitch control law is adopted to adjust the blade pitch angle, and a new adaptive super-twisting extended state observer is constructed to achieve total disturbance observation. Finally, simulations are conducted under two cases of wind and wave conditions based on FAST (fatigue, aerodynamics, structures, and turbulence) and MATLAB/Simulink. Compared with the traditional proportional integral (PI) control scheme and standard super-twisting control scheme, the platform roll under the proposed scheme is reduced by 13% and 4%, and pitch is reduced by 16% and 3% in Case 1. Correspondingly, the roll is reduced by 9% and 15%, and pitch is reduced by 7% and 1% in Case 2. For the tower top pitch and yaw moment, load reductions of 7% and 3% or more are achievable compared with those under the PI control scheme. It is indicated that the proposed scheme is more effective in suppressing floating platform motion, stabilizing output power of the wind turbine system, and reducing tower loads.

Improved pitch control strategy for the robust operation of wind energy conversion system in the high wind speed condition

The wind energy conversion system is a complex dynamic system with strong nonlinearity, perturbation, and uncertainty. In this paper, a novel optimal pitch control strategy is proposed to improve the ability to stabilize the captured wind energy, so as to realize robust operation in the high-wind-speed condition for wind turbines (WT) subject to unmodeled system disturbances and uncertainty. This control strategy combines three critical techniques: optimal pitch control law determination, disturbance compensation, and acceleration estimation. Among them, the optimal pitch control law is determined by utilizing the Hamilton-Jacobi-Bellman equation, regarding the minimization of the quadratic performance index. The total system uncertain disturbance is compensated by a designed extended state observer, making the pitch control approach almost independent of precise WT model parameters, markedly reinforcing the control system robustness. To prevent system noise amplification from direct differential means in acquiring rotor acceleration, we employ a fast-converging acceleration estimator to obtain the rotor acceleration feedback signal required by the pitch control law. System stability is proved using the Lyapunov theory. The comparative results on the developed hardware-in-the-loop test platform validate the effectiveness of the proposed solution, demonstrating that it provides superior dynamic performance in WT electrical power and speed with reduced fluctuation, overshoot, and regulation time while maintaining robustness against disturbances.

Aerodynamic Identification and Control Law Design of a Missile Using Machine Learning

The new generation of air vehicle is confronted with a more intricate environment and challenging missions, which puts forward higher requirements for the flight control system. In this study, the aerodynamic identification and control law design based on machine learning for a missile configuration is investigated through numerical simulations. The missile pitch and elevator deflection are realized via the combination of a rigid dynamic grid method and an overlapping grid technology, while the computational fluid dynamics/rigid body dynamics (CFD/RBD) strong coupling method is implemented to simulate the unsteady flows associated with the motion of the missile. Firstly, the aerodynamic data of the missile are gathered through forced pitching motion involving elevator deflection, and an aerodynamic model is constructed using a deep neural network to identify the aerodynamic moment with only a small number of unsteady aerodynamic data. Then, the accuracy and fidelity of the model are checked with the open-loop control law. Afterward, a missile pitch control law is generated through deep reinforcement learning based on the aerodynamic model, which enables the realization of a robust and exact angle-of-attack control process. Finally, the control law is transferred to a numerical environment and numerical virtual flight based on CFD is conducted, which demonstrates that stable control can be maintained even in continuous maneuvering. This study verifies the possibility of applying a deep neural network to air vehicle aerodynamic identification and deep reinforcement learning to a complicated flight control law design with excellent generalization ability. Machine learning is expected to play a significant role in the design and research for the novel generation of air vehicle.

A synthesis of a blade pitch control for large wind turbines, taking into account the functional dependence of the torque generated in the blades from the azimuth angle

In multi-MW (1MW and up) wind generation systems a variable speed - variable pitch (VS-VP) control technology is usually adopted to improve speed and torque characteristics and to obtain the optimal energy, which means to obtain the maximum power at low wind speed and the rated power at high wind speed. The power generated by an individual blade of the wind turbine changes considerably during rotation due for the change of wind speed in vertical direction, which decreases the angles of attack in the low blade positions and which leads to a reducing the generated energy. In the paper basing on BEM theory modification for none-homogenously fluid field and an optimization procedure is obtained an individual variable pitch control law as function of wind speed values and blades positions.

Operation of Darrieus turbines in constant circulation framework

Analytical and computational studies of flow across a low-speed marine turbine of Darrieus type with pitching blades have been carried out for flowfield and performance evaluation. The objective of this study is to develop efficient blade pitching laws to arrest or control the vortex shedding from the blades during turbine’s operation. This is achieved by imparting an arbitrary constant amount of circulation to the blades, where Kelvin’s theorem is respected. This paper presents the extension of the application of conformal mapping to produce the time-dependent flow over a rotating turbine blade in order to develop a quantified relationship between the blade’s orientation with respect to the rotor’s tangent and its rotational motion. The flow development is based on the analytical treatment given to potential flow formulation through Laurent series decomposition, where the Kutta condition is satisfied. The pitch control law and the analytical modeling of the hydrodynamic forces acting on the blade are derived based on Kelvin’s theorem for the conservation of circulation. The application of this pitch control law in the real flow conditions is however limited due to viscous losses and rotational effects. Therefore, a 2D computational fluid dynamics (CFD) study with the shear stress transport (SST) k–ω turbulence model has been performed to examine the flow across a 4-bladed turbine model. While validating the analytical work, the numerical investigation reveals the applicability and limitations of circulation-controlled blade pitching laws in real flow conditions. In particular, a reference equivalent angle of attack is defined, which must be contained in a tight range in order to effectively prevent vortex shedding at a given tip-speed ratio.

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.

Fault Diagnosis and Fault-Tolerant Control of Wind Turbines via a Discrete Time Controller with a Disturbance Compensator

This paper develops a fault diagnosis (FD) and fault-tolerant control (FTC) of pitch actuators in wind turbines. This is accomplished by combining a disturbance compensator with a controller, both of which are formulated in the discrete time domain. The disturbance compensator has a dual purpose: to estimate the actuator fault (which is used by the FD algorithm) and to design the discrete time controller to obtain an FTC. That is, the pitch actuator faults are estimated, and then, the pitch control laws are appropriately modified to achieve an FTC with a comparable behavior to the fault-free case. The performance of the FD and FTC schemes is tested in simulations with the aero-elastic code FAST.

Sliding Mode Control Applied to a Mini-Aircraft Pitch Position Model

Normally, mini-aircraft must be able to perform tasks such as aerial photography, aerial surveillance, remote fire and pollution sensing, disaster areas, road traffic and security monitoring, among others, without stability problems in the presence of many bounded perturbations. The dynamical model is affected by blast perturbations. Based on this, it is possible to design, evaluate and compare the real result with respect to pitch control law based on reference trajectory in the presence of external disturbances (blasts) or changes in the aircraft controller model. The model has non-linear properties but, with soft perturbations through the aircraft trajectory, allows a linear description without losing its essential properties. The Laplace description is a transfer function that works to develop the state space, with unknown invariant parameters using a wind tunnel. Control law is based on a feedback sliding mode with decoupled disturbances, and the output result is compared with the real pitch position measured in the real system. The control law applied to the system has a high convergence performance.

Sliding Mode Control Applied to a Mini-Aircraft Pitch Position Model

Normally, mini-aircraft must be able to perform tasks such as aerial photography, aerial surveillance, remote fire and pollution sensing, disaster areas, road traffic and security monitoring, among others, without stability problems in the presence of many bounded perturbations. The dynamical model is affected by blast perturbations. Based on this, it is possible to design, evaluate and compare the real result with respect to pitch control law based on reference trajectory in the presence of external disturbances (blasts) or changes in the aircraft controller model. The model has non-linear properties but, with soft perturbations through the aircraft trajectory, allows a linear description without losing its essential properties. The Laplace description is a transfer function that works to develop the state space, with unknown invariant parameters using a wind tunnel. Control law is based on a feedback sliding mode with decoupled disturbances, and the output result is compared with the real pitch position measured in the real system. The control law applied to the system has a high convergence performance.

Comparison of Inverse Optimal and Tuning Functions Designs for Adaptive Missile Control

An inverse optimal adaptive backstepping technique is applied to the design of a pitch control law for a generic surface-to-air nonlinear missile model, which is aerodynamically controlled. The control objective is to track a commanded reference signal with the angle of attack in the presence of control surface damage and aerodynamic uncertainties. The nonlinear adaptive control law is designed using a control Lyapunov function, after which inverse optimality with respect to a meaningful cost functional is demonstrated. The dynamic parameter update laws of the controller have been augmented with e-modification terms and dead-zones to prevent parameter drift. A second pitch control law is designed by means of the well known tuning functions adaptive backstepping technique. Both control laws are evaluated using numerical simulations where several cases of uncertainty are considered, after which a comparison of their nominal and robust performance is made.

On a pitch control law for a constant glide slope through windshears

SummaryThe equations of motion of an aircraft flying at a constant glide slope (Fig. 3), in the presence of arbitrary head- or tailwinds, and up- or downflows is considered. The equations are integrated analytically, in the case of an aircraft initially on a steady flight, perturbed by winds of ‘moderate’ strength, in the sense that the wind velocity is not negligible compared to the aircraft's steady speed, but the ratio of their squares is much smaller than unity. The case of an approach through a downburst (Fig. 1), leads to winds which can be simplified to a one-period sinusoidal wind along the flight path, changing from head- to tailwind, at the peak of a superimposed downflow (Fig. 2), of half-period sinusoidal shape, and this is discussed in some detail. Data sheets are presented for three combinations of amplitudes of the head-to-tailwind and downflow; each contains plots of the scheduling of incidence that exactly cancels windshear effects, and of the groundspeed a'nd airspeed profiles which will keep the aircraft flying along the original glide slope. Each plot is given for a range of values of the windshear susceptibility parameter, representing aircraft with small or large inertia, with high or low approach speeds, including light aircraft, jet fighters and large transports; the cancellation of windshear effects isachievable only if the incidence schedule lies wholly below the stall limit. Since the rotational inertia of the aircraft is neglected, the short period mode is absent, and the pitch control acts to cancel the ‘phugoid’ instability induced on the aircraft by the wind profiles typical of a microburst.