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

With the gradual increase in the installed capacity of wind turbines, more and more attention has been paid to the economy of wind power. Economic model-predictive control (EMPC) has been developed as an effective advanced control strategy, which can improve the dynamic economy performance of the system. However, the variable-speed wind turbine (VSWT) system widely used is generally nonlinear and highly coupled nonaffine systems, containing multiple economic terms. Therefore, a nonlinear EMPC strategy considering power maximization and mechanical load minimization is proposed based on the comprehensive VSWT model, including the dynamics of the tower and the gearbox in this paper. Three groups of simulations verify the effectiveness and reliability/practicability of the proposed nonlinear EMPC strategy.

https://www.mdpi.com/1996-1073/13/1/184/pdf

Wind Turbine Control Using Nonlinear Economic Model Predictive Control over All Operating Regions

The penetration of renewable distributed energy resources, such as wind turbine, has been dramatically increased in distribution networks. Due to the intermittent property, the wind power generation patterns vary, which may risk distribution network operations. So, it is intrinsically necessary to monitor wind turbines in a distributed way. This paper presents an adaptive-then-combine distributed dynamic approach for monitoring the grid under lossy communication links between the wind turbines and energy management system. First, the wind turbine is represented by a state-space linear model, with sensors deployed to obtain the system state information. Based on the mean squared error principle, an adaptive approach is proposed to estimate the local state information. The global estimation is designed by combining estimation results with weighting factors which are calculated by minimizing the estimation error covariance based on semidefinite programming. Finally, the convergence analysis indicates that the estimation error is gradually decreased, so the estimated state converges to the actual state. The efficacy of the developed approach is verified using the wind turbine and the IEEE 6-bus distribution system.

/pdf/an-adaptive-then-combine-dynamic-state-estimation-13gms1mn31.pdf

An Adaptive-Then-Combine Dynamic State Estimation Considering Renewable Generations in Smart Grids

Detection of power quality disturbances using an adaptive process noise covariance Kalman filter

In addition to human error, manufacturing tolerances for blades and hubs cause pitch angle misalignment in wind turbines. As a consequence, a significant number of turbines used by existing wind farms experience power production loss and a reduced turbine lifetime. Existing techniques, such as photometric technology and laser-based methods, have been used in the wind industry for on-field pitch measurements. However, in some cases, regular techniques have difficulty achieving good and accurate measurements of pitch angle settings, resulting in pitch angle errors that require cost-effective correction on wind farms. Here, the authors present a novel patented method based on laser scanner measurements. The authors applied this new method and achieved successful improvements in the Annual Energy Production of various wind farms. This technique is a benchmarking-based approach for pitch angle calibration. Two case studies are introduced to demonstrate the effectiveness of the pitch angle calibration method to yield Annual Energy Production increase.

Pitch Angle Misalignment Correction Based on Benchmarking and Laser Scanner Measurement in Wind Farms

Variable speed wind turbine is a complex and nonlinear system, a sophisticated control is required to meet the challenges posed by these systems. This paper is presenting a pitch regulation strategy based on LQG (Linear Quadratic Gaussian) to regulate turbine at its rated power and to reject the effect of disturbance acting on its rotor blades by wind. CART2 (Control Advanced Research Turbine) linear model is produced/generated by FAST (Fatigue, Aerodynamics, Structures and Turbulence) code to test its simulation on MATLAB/Simulink and various results are compared. The designed controller provide better disturbance rejection performance as compared to PID controller.

LQG controller design for pitch regulated variable speed wind turbine

Disturbance Accommodation Control (DAC) is used to model and simulate a system with known disturbance wave- form. This paper presents a control scheme to mitigate the effect of disturbances by using collective pitch control for the above- rated wind speed (Region III) for a variable speed wind turbine. We have used Linear Quadratic Regulator (LQR) to obtain full state feedback gain, disturbance feedback gain is calculated independently and then estimator gain is achieved by pole- placement technique in the DAC augmented plant model. The reduced order model (two-mass model) of wind turbine is used and 5MW National Renewable Energy Laboratory (NREL) wind turbine is used in this research. We have shown comparison of results relating to pitch angle, drive train torsion and generator speed obtained by a PID controller and DAC. Simulations are performed in MATLAB/Simulink. The results are compared with PID controller for a step wind and also for turbulent wind disturbance. DAC method shows better regulation in output power and less fatigue of drive train in the presence of pitch actuator limits. Proposed controller tested on wind turbine shows better robustness and stability as compared to PID. The paper describes practical experiences to develop a new DC power plant controller user interface based on human- centered design ideas.

DAC with LQR Control Design for Pitch Regulated Variable Speed 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.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-rpg.2016.0448

Optimal Tuning of Multivariable Disturbance-Observer-Based Control for Flicker Mitigation Using Individual Pitch Control of Wind Turbine

Wind Turbine is highly nonlinear plant whose dynamics changes with change in aerodynamics of the rotor blade. Power extracted from the wind turbine is a function of coefficient of power (Cp). Wind turbine installed in the cold climate areas has an icing on its rotor blade which might change its aerodynamics. This paper is an experimental investigation of the aerodynamic changes occur due to effect of ice accumulated on the rotor blades of wind turbine. We have tested three small scale model of the NREL's 5MW rotor blade with same profile but simulated different icing effect on them. These models are printed with 3D printer and tested one by one in a Wind Tunnel. Lift, drag and moment coefficients are calculated from the measured experimental data and program WT-Perf based on blade-element momentum (BEM) theory is used to predict the performance of wind turbine. Cp curves generated from the test are compared with each other to see the effect of icing effect however Cp curve of the clean blade generated from the experiment is compared with the Cp curve from the NREL's 5MW rotor blade airfoil to see the effect of the limitation of the project. It is clear from the results that the rotor blade with lead edge ice has less peak value and shape of the Cp curve is unchanged as compared to clean blade. However the blade with lead and trail edge ice has reduced peak value but shape of the Cp curve is changed as compared to clean and lead edge ice blade.

An experimental analysis of the effect of icing on Wind turbine rotor blades

This paper is concerned with bump-less transfer of parameterized disturbance observer based controller with individual pitch control strategy to reduce cyclic loads of wind turbine in full load operation. Cyclic loads are generated due to wind shear and tower shadow effects. Multivariable disturbance observer based linear controllers are designed with objective to reduce output power fluctuation, tower oscillation and drive-train torsion using optimal control theory. Linear parameterized controllers are designed by using a smooth scheduling mechanism between the controllers. The proposed parameterized controller with individual pitch was tested on nonlinear Fatigue, Aerodynamics, Structures, and Turbulence (FAST) code model of National Renewable Energy Laboratory (NREL)’s 5 MW wind turbine. The closed-loop system performance was assessed by comparing the simulation results of proposed controller with a fixed gain and parameterized controller with collective pitch for full load operation of wind turbine. Simulations are performed with step wind to see the behavior of the system with wind shear and tower shadow effects. Then, turbulent wind is applied to see the smooth transition of the controllers. It can be concluded from the results that the proposed parameterized control shows smooth transition from one controller to another controller. Moreover, 3p and 6p harmonics are well mitigated as compared to fixed gain DOBC and parameterized DOBC with collective pitch.

Raja Muhammad Imran

Papers

LQG controller design for pitch regulated variable speed wind turbine

DAC with LQR Control Design for Pitch Regulated Variable Speed Wind Turbine

Optimal Tuning of Multivariable Disturbance-Observer-Based Control for Flicker Mitigation Using Individual Pitch Control of Wind Turbine

An experimental analysis of the effect of icing on Wind turbine rotor blades

Parameterized Disturbance Observer Based Controller to Reduce Cyclic Loads of Wind Turbine