Ensuring safe operation at all times and in all conditions is one of the primary goals of wind turbine control systems. This paper presents a novel approach for wind turbine control based on the ...concept of envelope riding. The proposed approach utilizes on-line numerical optimization to predict at each time instant the extremal wind speed that would lead the machine to encounter the envelope of its safe operating range. Based on this extremal condition, control inputs are computed that maintain the response within the safe region at all times, at the most riding its boundary but without ever leaving it. The method is capable of keeping the machine within its safe envelope within the entire range of operating wind speeds, including both rated and cut-out conditions.
The new method is verified with the help of numerical simulations conducted with a high-fidelity aeroservoelastic environment. Comparisons are made with standard control algorithms for the prevention of excessive loading, including peak-shaving and soft cut-out schemes. Results illustrate the ability of the proposed approach in reducing loads and improving power output.
•New concept: wind turbine response is monitored on-line to ensure that it stays at all times within the safe envelope.•Applicable to the whole wind speed range, including rated and cut-out.•Dynamic approach improves on peak-shaving and soft-cut-out methods based on static characteristics computed off-line.•Results in convex optimization problem, solved efficiently in real-time and in a deterministic number of operations.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
An aeroelastically scaled model of a wind turbine is described, featuring active individual blade pitch and torque control. The model, governed by supervision and control systems similar to those of ...a real wind turbine, is capable of simulating steady conditions and transient maneuvers in the boundary layer test section of the wind tunnel of the Politecnico di Milano. Expanding the classical scope of wind tunnel models, the present experimental facility enables applications ranging from aerodynamics to aeroelasticity and control.
After a description of the model design and of its main characteristics, several applications are presented. Results are shown for the validation of a wind misalignment observer, for the optimization of the open-loop pitch profile used during emergency shutdowns, for the control in wake interference conditions of two models, and for active load alleviation by higher harmonic individual blade pitch control. Results demonstrate the potential of the proposed experimental facility to enable non-standard observations in the controlled environment of the wind tunnel, beyond the classical purely aerodynamic ones.
•Aeroelastically scaled wind tunnel model with active individual blade pitch and torque control.•Highly sensorized model, complete with full array of hardware and software support equipment.•Model capable of supporting studies in aerodynamics, aeroservoelasticity and controls.•Experimental validation of new controls and estimation concepts for wind turbines.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper presents results from wind tunnel tests aimed at evaluating a closed- loop wind farm controller for wind farm power maximization by wake deflection. Experiments are conducted in a large ...boundary layer wind tunnel, using three servo-actuated and sensorized wind turbine scaled models. First, we characterize the impact on steady-state power output of wake deflection, achieved by yawing the upstream wind turbines. Next, we illustrate the capability of the proposed wind farm controller to dynamically driving the upstream wind turbines to the optimal yaw misalignment setting.
The reduction of structural loads is becoming an important objective for the wind turbine control system due to the ever‐increasing specifications/demands on wind turbine rated power and related ...growth of turbine dimensions. Among various control algorithms that have been researched in recent years, the individual pitch control has demonstrated its effectiveness in wind turbine load reduction. Since the individual pitch control, like other load reduction algorithms, requires higher levels of actuator activity, one must take actuator constraints into account when designing the controller. This paper presents a method for the inclusion of such constraints into a predictive wind turbine controller. It is shown that the direct inclusion of constraints would result in a control problem that is nonconvex and difficult to solve. Therefore, a modification of the constraints is proposed that ensures the convexity of the control problem. Simulation results show that the developed predictive control algorithm achieves individual pitch control objectives while satisfying all imposed constraints.
Full text
Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this paper, a model predictive control (MPC) is proposed for wind farms to minimize wake-induced power losses. A constrained optimization problem is formulated to maximize the total power ...production of a wind farm. The developed controller employs a two-dimensional dynamic wind farm model to predict wake interactions in advance. An adjoint approach as an efficient tool is utilized to compute the gradient of the performance index for such a large-scale system. The wind turbine axial induction factors are considered as the control inputs to influence the overall performance by taking the wake interactions into account. A layout of a 2 × 3 wind farm is considered in this study. The parameterization of the controller is discussed in detail for a practical optimal energy extraction. The performance of the adjoint-based model predictive control (AMPC) is investigated with time-varying changes in wind direction. The simulation results show the effectiveness of the proposed approach. The computational complexity of the developed AMPC is also outlined with respect to the real time control implementation.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Owing to the aerodynamic conversion process, wind turbines exhibit a nonlinear behavior and encounter turbulent operating conditions that demand well-defined closed-loop dynamics to withstand ...accumulated loading over the lifetime. Wind excitation is the main disturbance and driving force for the system and determines the necessary operating strategy, but it usually represents an unmeasurable quantity. In this study, we used a linear-matrix-inequalities-based control and observer design to operate a variable-speed, variable-pitch wind turbine in a wind tunnel experiment at different reproducible inflow conditions while relying on a wind speed estimate obtained from a disturbance observer. The computational complexity of the stability framework incorporating the reconstruction of the unknown wind speed is reduced by exploiting characteristics of the modeling approach based on a convex combination of linear submodels. The assumption used in the proposed stability consideration is evaluated based on measurement data. We introduced an extended operating range compared to the commonly considered operating trajectory of wind turbines in the control design. A controller based on Takagi–Sugeno modeling is used to operate the turbine at challenging power tracking requirements demonstrating the capability to support fast stabilization of the electrical grid while discussing the loading and operational constraints observed during the experiments.
Display omitted
•Nonlinear model-based control design using linear matrix inequalities was performed.•The control design was applied to a wind turbine to provide power tracking capability.•Proof of stability of the observer-based strategy considering unmeasurable wind speed was realized.•Experimental wind tunnel validation in a large operational range under reproducible turbulent inflow conditions was attained.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The flow inside a typical large wind from propagates through the array from turbine to turbine. We present an algorithm that intuitively processes measured values from as much as possible turbines in ...real-time and uses them to determine a flow reconstruction and minute-scale forecast for the downstream turbines. For the validation we used full-field measurements from the offshore wind farm Global Tech I. The flow reconstruction is compared to the measurements of one turbine, which was excluded from the algorithm and achieved a root mean square error of 0.55 ms−1 for the wind speed estimation. The flow forecasting is tested for three prediction horizons 30s, 60s and 120s. Together with automated error correction to account for calibration errors and wake effects, the flow prediction achieves a root mean square error of 0.52 ms−1 for the 120s-forecast of the wind speed, which beats the persistence forecasting method. The reconstruction allows to analyse the flow in the wind farm, to detect abnormal turbine behaviour and to estimate fatigue loads, and the minute-scale forecasting is a useful tool for predictive wind farm control and estimating the available power of a wind farm, which becomes more and more necessary for grid stability.
Wind turbines are typically closely spaced in wind farms, and thus operate in the wake of upstream turbines and experience power losses. Currently, one of the techniques to reduce the wake ...interaction between turbines within a wind farm is to yaw the upstream turbine with regards to the incident wind direction. The objective is to deflect the wake, which can potentially increase the overall power output and the annual energy production of the wind farm. Experimental data can aid the process to thoroughly analyse the wake deflection under different inflow conditions, which is necessary to apply a yaw-based wind farm control model. The aim of the present research is to investigate the possibility and accuracy of the experimental setup to measure the wake characteristics with a high spatial and temporal resolution through the use of a short-range Lidar WindScanner, within the wind tunnel of ForWind-Oldenburg. This technique provides the opportunity to analyse the flow structures at different operational and inflow conditions in a relative fast manner without disturbing the flow. Experiments were conducted using a model wind turbine in a large cross-section wind tunnel. The short-range Lidar WindScanner is used as the primary instrument to map the wind turbine wake at different downstream locations. The flow structures of the wake were measured from 1 D up to 10 D downstream of the turbine rotor. A stable flow within the wind tunnel segment is measured, which is crucial for the analyses of the evolution of the wake. In addition, a high detailed spatial resolution of the wake profile is observed, showing the symmetric and asymmetric behaviour of the wake, for unyawed and yawed conditions, respectively. Furthermore, the calculation of the thrust coefficient from the velocity data show expected behaviour, giving further credibility to the measurement technique.
Wind tunnel experiments with scaled model turbines are a viable complement to field tests and simulations. The scaling of a 5 MW reference turbine with the aim of maintaining the design tip speed ...ratio and lift distribution is introduced. The machine, named MoWiTO 1.8 (Model Wind Turbine Oldenburg 1.8 m), is described in this paper and the setup in the WindLab wind tunnel of the University of Oldenburg, featuring an active grid, is described. Based on aerodynamic simulations in a turbulent wind field flow, the calculated aerodynamic loads of the reference turbine and the scaled model are compared. Furthermore, the aerodynamic characterization of the machine is presented, with focus on power and thrust coefficients and sensitivity to changes in the Reynolds number. It is shown, that with the chosen approach many attributes of the reference turbine can be scaled into the controllable wind tunnel environment.
PDF
