Disturbance Accommodating Control Research Articles

Independent Pitch Adaptive Control of Large Wind Turbines Using State Feedback and Disturbance Accommodating Control

Wind turbines experience significant unbalanced loads during operation, exacerbated by external disturbances that challenge the stability of the pitch control system and affect output power. This paper proposes an independent pitch adaptive control strategy integrating state feedback and disturbance accommodating control (DAC). Initially, nonlinear wind turbine dynamics are globally linearized, and DAC is applied to mitigate the impact of wind disturbances dynamically. Subsequently, the entire range of wind speeds is segmented, and controllers are individually designed to optimize gain settings according to specific control objectives at each wind speed interval. Scheduling parameters such as collective pitch angle and tower fore-aft displacement are identified and trained using Radial Basis Function Neural Networks (RBFNN). Finally, based on the output gain values determined by RBFNN, the full-state feedback controller group is adaptively adjusted, and the optimal controller is selected for the final output. Simulations conducted on the NREL 5MW reference wind turbine model using FAST and Simulink demonstrate that compared to the ROSCO controller, the proposed strategy ensures smoother output power and effectively reduces blade and tower loads, thereby extending the turbine’s operational lifespan.

Integrated control strategy for the vibration mitigation of wind turbines based on pitch angle control and TMDI systems

Modern wind turbines are becoming taller and more slender to gather wind energy more efficiently and are increasingly installed in complex environments. Consequently, the new generations of wind turbines are prone to vibration-related problems, making the development of vibration control strategies important. Various pitch angle control methods and dynamic vibration absorbers (DVAs) have been proposed recently to reduce the aerodynamic forces and structural responses of wind turbines. However, these approaches are often implemented independently, limiting the effectiveness of the overall control strategy. In this paper, pitch angle control and DVAs are integrated to improve the performance of wind turbines in a complex environment. Firstly, a simplified eight degree-of-freedoms (DOFs) model of the wind turbine is developed using Lagrange’s Equation, and the wind turbine is linearized at specific operating points. The NREL 5MW wind turbine is taken as a benchmark model with strategies based on a proportional–integral (PI) pitch controller. Secondly, the pitch angle of each blade is adjusted by the combination of disturbance accommodating control (DAC) and linear quadratic gaussian (LQG) controller considering the wind speed disturbances. Additionally, the tuned mass damper with inerter (TMDI) is adopted to further suppress the structural vibrations. Thirdly, the passive and active methods of TMDl integrated with the pitch controller are investigated. Lastly, the effectiveness of the integrated control strategies is assessed when the wind turbines are subjected to earthquake and wind loads. The results indicate that combining active pitch control and TMDI can improve the power generation performance of wind turbines by reducing structural responses and damage-equivalent loads, and can also improve the power generation performance more effectively than when they are used separately.

Observer-Based Disturbance Accommodation Control Strategy for Useful Lifetime Control and Structural Load Mitigation of Wind Turbines

Wind turbines undergo degradation due to various factors which induce stress, thereby leading to fatigue damage to various wind turbine components. In addition, the current increase in demand for electrical power has led to the development of large wind turbines, which result in increased structural loads, therefore, increasing the possibility of early failure due to fatigue load. This paper proposes a proportional integral observer (PI-Observer) based disturbance accommodation controller (DAC) with individual pitch control (IPC) for load mitigation to reduce components’ damage and ensure the wind turbine is operational for the expected lifetime. The results indicate a reduction in blades’ bending moments with a standard deviation of 15.9%, which positively impacts several other wind turbine subsystems. Therefore, the lifetime control strategy demonstrates effective structural load mitigation without compromise on power generation, thus, achieving a nominal lifetime control to inhibit premature failure.

LIDAR-Assisted Exact Output Regulation for Load Mitigation in Wind Turbines

Optimizing wind turbine performance involves maximizing energy harvesting while seeking to minimize load fatigues on the tower structure, blades, and rotor. To improve turbine control performance, wind preview measurement technologies, such as light detection and ranging (LIDAR), have been a point of interest for researchers in recent years. In this article, we explore the application of a classical control methodology known as exact output regulation (EOR) for improving the control performance of a LIDAR-enhanced wind turbine. The EOR controller is designed to achieve the rejection of known input disturbances, while also ensuring the system output tracks the desired reference signal. The controller is comprised of a state feedback controller together with a feedforward gain. The LIDAR wind preview information is used to obtain a low-order exosystem for modeling wind dynamics. This wind exosystem is used to obtain the feedforward gain matrix that enables the EOR controller to effectively reject the input disturbance and achieve the desired reference tracking. Extensive simulations of the EOR controller with a broad range of wind speeds in both partial load and full load operating regions are performed on the full nonlinear aero-elastic model of the National Renewable Energy Laboratory 5-MW reference wind turbine. For performance comparisons, we also implement a Baseline torque controller and a commonly used feedforward control method known as disturbance accommodation control (DAC). The results show that, in comparison with a baseline and DAC controller, the EOR controller can provide a substantially improved reduction of fatigue loads and smoother power output, without compromising energy production levels.

Fault tolerant control of wind turbines with an adaptive output feedback sliding mode controller

Wind turbines are developed to generate electrical energy with more efficiency and reliability. Modern fault detection, diagnosis, and accommodation structures are crucial to realize required level of reliability and efficiency for wind turbines. In this paper, a novel active fault tolerant controller is addressed to control rotor speed and power of a wind turbine in the presence of actuator faults and uncertainties. The proposed controller is a sliding mode controller with an integral surface and an adaptive gain which is known as adaptive output feedback sliding mode controller. An output feedback and a full-order compensator are utilized to shape the integral sliding surface and control law. The full-order compensator is proposed for fault and disturbance attenuation. The control law parameters adjustment and closed-loop system stability are satisfied using linear matrix inequality technique and Lyapunov stability theorem, respectively. Efficiency of the suggested controller is tested on a 5-MW wind turbine benchmark model in an extreme wind speed profile. In this regard, performance of the proposed strategy is compared with proportional-integral-derivative and disturbance accommodation control techniques. Simulation results show desirable performance and robustness behaviour for the adaptive output feedback integral sliding mode controller under the healthy and faulty actuator.

Optimal Pitch Control Design With Disturbance Rejection for the Controls Advanced Research Turbine

Advanced and model-based control techniques have become prevalent in modern wind turbine controls in the past decade. These methods are more attractive compared to the commonly used proportional-integral-derivative (PID) controller, as the turbine structural flexibility is increased with multiple and coupled modes. The disturbance accommodating control (DAC) is an effective turbine control approach for the above-rated wind speed region. DAC augments the turbine state-space model with a predefined disturbance waveform model, based on which the controller reduces the impact of wind disturbances on the system output (e.g., rotor speed). However, DAC cannot completely reject the wind disturbance in certain situations, and this results in steady-state regulation errors in the turbine rotor speed and electric power. In this paper, we propose a novel wind turbine pitch control using optimal control theory. The obtained feedback and feedforward control terms function to stabilize the turbine system and reject wind disturbances, respectively, derived systematically based on the Hamilton–Jacobi–Bellman (HJB) equation. Simulation results show that the proposed method achieves desired rotor speed regulation with significantly reduced steady-state errors under turbulent winds, which is simulated on the model of the three-bladed controls advanced research turbine (CART3) using the FAST code.

Adaptive State Feedback Pitch Angle Control of Wind Turbines for Speed Regulation and Blades Loadings Alleviation

This research article presents an adaptive state feedback blades pitch control of wind turbines for speed regulation and structural blades loadings mitigation in high wind speeds. The proposed control is a combination of a state feedback control and an integrator. It enables to improve the generator speed tracking, as well as to reduce the flap-wise bending moment at the root of the blades. The motivation principal of the proposed controller is that its structure allows surpassing the trade-off between the control objectives. The control scheme is tested on the NREL’s FAST 5 MW baseline wind turbine model in MATLAB/Simulink under different wind speed profiles and its performances are compared with those of the baseline gain scheduling proportional integral (GSPI) control and the disturbance accommodation control (DAC). The simulation results enable to conclude that the proposed controller has good performances in term of generator speed tracking as well as blade root flap-wise bending moment fluctuations reduction. Moreover, the controller is tested to be robust under system uncertainties.

Load reduction based on a stochastic disturbance observer for a 5 MW IPC wind turbine

Control and operation systems of wind turbines must primarily ensure the fully automatic operation of wind turbines in a constantly changing environment. Economic efficiency charges the control system to ensure that the highest possible efficiency is achieved and the mechanical loads caused by disturbances are minimized. The ability of an observer, in this case a Kalman filter (Kf), to estimate non-measurable states from a set of measurements using a model of the plant suggests the idea of extending the model of the plant by a model of the disturbance. Disturbance states thus can be reconstructed and an easy-to-determine quasi-disturbance-feedforward controller can be used to reject them. This method is called Disturbance-Accommodating Control (DAC). In this paper, Dryden’s turbulence model-which shapes a white noise signal via a form filter to meet spectrum conditions - and an inverse notch filter to model the rotational sampling effect are used for each blade, in contrary to the hitherto used deterministic disturbance models or the simple random walk models for stochastic turbulence. Measurement- and model-uncertainties are described as uncorrelated white noise. With this approach, the requirements of the Kf derivation are met and quantitative measures for the Kf process noise covariance matrix are available especially for the disturbance. The simplified tuning process and the high potential for load reduction are demonstrated for the NREL 5 MW Wind turbine. The reduction by a factor of 4.4 of the standard deviation of the flapwise root bending moment shows the high potential of this stochastic DAC approach. A parameter study to determine the influence of the turbulence spectrum bandwidth and to identify the dependency of the stochastic DAC approach on uncertainties of the process noise covariance matrix was performed. The study shows that the Kf is robust against a wide spectrum of parameter variations. Only if the time constant of the Dryden filter is significantly reduced, the performance is decreased.

Active load control of large wind turbines using state-space methods and disturbance accommodating control

The control of wind turbine loads is fundamental to reduce wind energy cost. Wind turbines are complex dynamic systems subjected to random wind loads and harsh operational vibrations. Active load control reduces wind turbine mechanical vibrations, provoking an increase in wind turbine components lifetimes and the design of lighter and more flexible parts, reducing wind turbine global cost. The pitch control system plays a decisive role in shaping the wind turbine dynamics. By using the appropriate control methods, it can be used to reduce the dynamic response in most of wind turbine components, given the fully-coupled system dynamics. In this paper, it is demonstrated the development of an active load control of the wind turbine tower loads using the pitch control system. State-space control is carried out to consider the coupled wind turbine dynamics and the disturbance accommodating control (DAC) is used to cancel the effect of wind disturbances in the dynamics of the overall system. The active load control is performed without damaging the aerodynamic power control.

Optimal Hybrid Magnetic Attitude Control: Disturbance Accommodation and Impulse Timing

A recently proposed hybrid attitude control scheme, which optimally combines magnetic torques with impulsive thrusting using a continuous/discrete linear quadratic regulator, is modified to accommodate disturbances. Accounting for the presence of disturbances in the design procedure, previous results on necessary conditions for optimality of impulse application times are modified accordingly. In addition, the special case of a multiorbit mission with repeating impulse patterns is considered, showing that an elegant extension of the optimality conditions would significantly reduce the computational cost by limiting the design space to only the first orbit: this extended condition is obtained by summing over all orbits within the control interval, the original conditions being computed at each repeating impulse time. Finally, numerical examples are presented, confirming the superiority of the proposed disturbance-accommodating controller in terms of steady-state performance (even when the disturbance estimates are partly incorrect) and the validity of the extended optimal timing theory in the linear region.

Disturbance Accommodating Control Design for Wind Turbines Using Solvability Conditions

In this paper, solvability conditions for disturbance accommodating control (DAC) have been discussed and applied on wind turbine controller design in above-rated wind speed to regulate rotor speed and to mitigate turbine structural loads. An asymptotically stabilizing DAC controller with disturbance impact on the wind turbine being totally canceled out can be found if certain conditions are fulfilled. Designing a rotor speed regulation controller without steady-state error is important for applying linear control methodology such as DAC on wind turbines. Therefore, solvability conditions of DAC without steady-state error are attractive and can be taken as examples when designing a multitask turbine controller. DAC controllers solved via Moore–Penrose Pseudoinverse and the Kronecker product are discussed, and solvability conditions of using them are given. Additionally, a new solvability condition based on inverting the feed-through D term is proposed for the sake of reducing computational burden in the Kronecker product. Applications of designing collective pitch and independent pitch controllers based on DAC are presented. Recommendations of designing a DAC-based wind turbine controller are given. A DAC controller motivated by the proposed solvability condition that utilizes the inverse of feed-through D term is developed to mitigate the blade flapwise once-per-revolution bending moment together with a standard proportional integral controller in the control loop to assist rotor speed regulation. Simulation studies verify the discussed solvability conditions of DAC and show the effectiveness of the proposed DAC control design methodology.

Adaptive pitch control of wind turbine for load mitigation under structural uncertainties

In this research, a new adaptive control strategy is formulated for the pitch control of wind turbine that may suffer from reduced life owing to extreme loads and fatigue when operated under high wind speed and internal structural uncertainties. Specifically, we aim at making a trade-off between the maximum energy captured and the load induced. The adaptive controller is designed to both regulate generator speed and mitigate component loads under turbulent wind field when blade stiffness uncertainties exist. The proposed algorithm is tested on the NREL offshore 5-MW benchmark wind turbine. The control performance is compared with those of the gain scheduled proportional integral (GSPI) control and the disturbance accommodating control (DAC) that are used as baselines. The results show that with the proposed adaptive control the blade root flapwise load can be reduced at a slight expense of optimal power output. Moreover, the blade load mitigation performance under uncertain blade stiffness reduction is improved over the baseline controllers. The control approach developed in this research is general, and can be extended to mitigating loads on other components.

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.

Disturbance-Observer-Based Control and Related Methods—An Overview

Disturbance-observer-based control (DOBC) and related methods have been researched and applied in various industrial sectors in the last four decades. This survey, at first time, gives a systematic and comprehensive tutorial and summary on the existing disturbance/uncertainty estimation and attenuation techniques, most notably, DOBC, active disturbance rejection control, disturbance accommodation control, and composite hierarchical antidisturbance control. In all of these methods, disturbance and uncertainty are, in general, lumped together, and an observation mechanism is employed to estimate the total disturbance. This paper first reviews a number of widely used linear and nonlinear disturbance/uncertainty estimation techniques and then discusses and compares various compensation techniques and the procedures of integrating disturbance/uncertainty compensation with a (predesigned) linear/nonlinear controller. It also provides concise tutorials of the main methods in this area with clear descriptions of their features. The application of this group of methods in various industrial sections is reviewed, with emphasis on the commercialization of some algorithms. The survey is ended with the discussion of future directions.

Preventing wind turbine overspeed in highly turbulent wind events using disturbance accommodating control and light detection and ranging

AbstractLight detection and ranging (LIDAR) systems can be used to provide wind inflow information to a wind turbine controller before the wind reaches the turbine. Both fatigue and extreme load reduction are possible as a result; in this research, we propose a LIDAR‐based controller designed to prevent emergency shutdowns caused by rotor overspeed. This switching controller consists of a disturbance accommodating control (DAC)‐based baseline controller and a different DAC linearized about a reduced generator speed for extreme events, also referred to as an extreme event controller. Switching between the controllers was performed using linear interpolation over various transition times, depending on how early the extreme event could be detected. If a gust of wind is detected using LIDAR measurements evaluated by a one‐sided cumulative summation algorithm, a relatively long transition time can be used. Switching can also be based on a large output estimation error, εy, in which case the transition time is shorter. Once the extreme event passed, control is switched from the extreme event controller back to the baseline DAC. This switching controller resulted in fewer overspeeds when compared with the modified baseline controller, which is a gain scheduled DAC. By preventing overspeeds, the switching controller increased the mean power the wind turbine generated over a simulated 10 min period. Copyright © 2014 John Wiley & Sons, Ltd.

Wind and Wave Disturbances Compensation to Floating Offshore Wind Turbine Using Improved Individual Pitch Control Based on Fuzzy Control Strategy

Due to the rich and high quality of offshore wind resources, floating offshore wind turbine (FOWT) arouses the attentions of many researchers. But on a floating platform, the wave and wind induced loads can significantly affect power regulation and vibration of the structure. Therefore, reducing these loads becomes a challenging part of the design of the floating system. To better alleviate these fatigue loads, a control system making compensations to these disturbances is proposed. In this paper an individual pitch control (IPC) system integrated with disturbance accommodating control (DAC) and model prediction control (MPC) through fuzzy control is developed to alleviate the fatigue loads. DAC is mainly used to mitigate the effects of wind disturbance and MPC counteracts the effects of wave on the structure. The new individual pitch controller is tested on the NREL offshore 5 MW wind turbine mounted on a barge with a spread-mooring system, running in FAST, operating above-rated condition. Compared to the original baseline collective pitch control (CPC) (Jonkman et al., 2007), the IPC system shows a better performance in reducing fatigue loads and is robust to complex wind and wave disturbances as well.

풍력발전시스템 개별피치제어설계 및 피로해석에 관한 연구

Structural loading on a wind turbine is due to cyclic loads acting on the blades under turbulence and periodic wind field. The structural loading generates fatigue damage and fatigue failure of the wind turbine. The individual pitch control(IPC) is an efficient control method for reducing structural loading. In this paper, we present an IPC design method using Decentralized LQR(DLQR) and Disturbance accommodating control(DAC). DLQR is used for regulating rotor speed and DAC is used for canceling out disturbances. The performance of the proposed IPC is compared with CPC, which was designed with a gain-scheduled PI controller. We confirm the effect of fatigue load reduction with the use of damage equivalent load(DEL).

Wind Turbine Pitch Control and Load Mitigation Using anL1Adaptive Approach

We present an application ofL1adaptive output feedback control design to wind turbine collective pitch control and load mitigation. Our main objective is the design of anL1output feedback controller without wind speed estimation, ensuring that the generator speed tracks the reference trajectory with robustness to uncertain parameters and time-varying disturbances (mainly the uniform wind disturbance across the wind turbine rotor). The wind turbine model CART (controls advanced research turbine) developed by the national renewable energy laboratory (NREL) is used to validate the performance of the proposedL1adaptive controller using the FAST (fatigue, aerodynamics, structures, and turbulence) code. A comparative study is also conducted between the proposed controller and the most popular methods in practice: gain scheduling PI (GSPI) controls and disturbance accommodating control (DAC) methods. The results show better performance ofL1output feedback controller over the other two methods. Moreover, based on the FAST software and LQR analysis in the reference model selection ofL1adaptive controller, tradeoff can be achieved between control performance and loads mitigation.

D16 建物と制御系の特性を考慮した免震床の外乱包含制御(M-OS2-2 免震・制振の制御系設計,M-OS2 建築・建設構造物の耐震・免震・制振,「海を越え,国を越え,世代を超えて!」)

In earthquakes, it becomes more important to maintain a normal function of equipment placed in a building. One of the most effective ways to reduce vibration is to place some control devices, such as on a building and on equipment. Although centralized control system can control effectively, it is vulnerable to failure. Therefore, to achieve better performance in distributed control system is needed. It is expected to improve performance by giving controller some information about noise. In this paper, we apply the Disturbance-Accommodating control to the equipment controller. The concept of the proposed method is to consider the characteristics of building and control system in frequency domain. From the result of simulations, the effectiveness is verified in distributed control system.

固定翼UAVにおける遷移飛行の制御系設計

This paper describes the design of novel control system for a fixed-wing Unmanned Aerial Vehicle (UAV) which can transition between level flight and hovering. The control system is constructed by using dynamic inversion method applying to the translational and rotational nonlinear equations of motion of the UAV. In the controller design for the rotational motion, an observer based on Disturbance Accommodating Control (DAC) method is used to estimate nonlinear parameters. Moreover, H∞ controller is employed to have robustness against estimation error and modeling error on its dynamics. In order to verify the validity of the proposed control system, numerical simulation is performed for the UAV.