Vlaho Petrović

Individual pitch control of wind turbine based on loads estimation

The use of wind energy for generating electricity has been constantly and rapidly increasing over last few decades and this growth is expected to continue. In order to enable even greater role of wind energy in power production wind turbinespsila sizes and rated powers must increase. As wind turbines grow in size they are subjected to extreme loads and fatigue caused by uniform turbulent winds. This prevents further growth of wind turbines. Therefore control methods that assure loads reduction become a necessity. In this paper methods for wind turbine loads reduction based on individual pitch control are explored. To overcome problems related to needed measurements of blade loads a method for their estimation based on loads measured on the fixed parts of the structure is proposed.

Estimation based Individual Pitch Control of Wind Turbine

The use of wind power for generating electricity has experienced an uninterrupted and accelerating growth over last few decades and this growth is likely to continue. In order to enable even greater role of wind energy in power production it is necessary to increase the size and unit power of wind turbines. As wind turbines grow in size they are subjected to extreme loads and fatigue caused by nonuniform turbulent winds. Therefore, control algorithms that can assure load and fatigue reduction become a necessity. In this paper the individual pitch control for reduction of the periodic blade and hub loading is explored. To avoid problems related to the required blade loads measurements a method for their estimation based on other process variables is proposed. The performance of the individual pitch controller that uses such load estimations instead of measurements is tested and compared to the collective pitch control and the individual pitch control based on measured loads.

Identification of wind turbine model for individual pitch controller design

The use of wind power has been increasing rapidly over last few decades and according to all predictions this trend is likely to continue. At the same time need for better cost effectiveness of wind power plants has stimulated growth in wind turbinespsila size and rated power. As wind turbines grow in size they are subject to extreme structural loads and fatigue. In order to reduce such loads advanced control methods are explored among which individual pitch control has demonstrated very promising results. To design an individual pitch controller suitable wind turbine model is required. Derivation of wind turbine model for individual pitch controller design is addressed in this paper.

Wind tunnel testing of wake control strategies

Goal of this paper is to present results from wind tunnel tests aimed at evaluating the potential of different wake control strategies for wind farm power maximization and load reduction. The experiments are conducted in a large boundary layer wind tunnel, using up to six servo-actuated and highly sensorized wind turbine scaled models in different wind farm layouts. Two main strategies are considered: the first derates the upstream wind turbines, while the second aims at redirecting wakes away from the downstream machines. The latter strategy is implemented in two alternative ways, using either active yawing or individual blade pitching. The impact on wind farm power and loading of these control strategies is discussed, highlighting the most promising ones.

Wind tunnel testing of a closed-loop wake deflection controller for wind farm power maximization

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.

Wind turbine optimal control during storms

This paper proposes a control algorithm that enables wind turbine operation in high winds. With this objective, an online optimization procedure is formulated that, based on the wind turbine state, estimates those extremal wind speed variations that would produce maximal allowable wind turbine loads. Optimization results are compared to the actual wind speed and, if there is a danger of excessive loading, the wind turbine power reference is adjusted to ensure that loads stay within allowed limits. This way, the machine can operate safely even above the cut-out wind speed, thereby realizing a soft envelope-protecting cut-out. The proposed control strategy is tested and verified using a high-fidelity aeroservoelastic simulation model.

Wind shear estimation and wake detection by rotor loads — First wind tunnel verification

The paper describes a simple method for detecting presence and location of a wake affecting a downstream wind turbine operating in a wind power plant. First, the local wind speed and shear experienced by the wind turbine are estimated by the use of rotor loads and other standard wind turbine response data. Then, a simple wake deficit model is used to determine the lateral position of the wake with respect to the affected rotor. The method is verified in a boundary layer wind tunnel using two instrumented scaled wind turbine models, demonstrating its effectiveness.

Wind Turbine Envelope Riding

This paper presents a power control algorithm that aims at keeping a wind turbine within its safe loading envelope at all times. An online optimization procedure is used to find those wind speed variations that would lead the wind turbine response to approach the border of the safe operating region, without crossing it. The optimization result is then compared to the actual wind speed to detect if there is a danger of excessive loading, in which case the power reference is adjusted accordingly. The method is the extension of a previously described optimal soft cut-out strategy, which is here modified in order to control the machine not only at high wind speeds but across the entire operating speed range. The proposed control strategy is verified using a high-fidelity aeroservoelastic simulation model, demonstrating its ability in riding the operating envelope, thereby keeping the wind turbine within safe limits at all times.

Reduction of wind turbine structural loads caused by rotor asymmetries

To enable further growth of wind turbine dimensions and rated power, it is essential to decrease structural loads that wind turbines experience. Therefore a great portion of research is focused on control algorithms for reduction of structural loads, but typically wind turbine rotor is considered to be perfectly symmetrical, and therefore such control algorithms cannot reduce structural loads caused by rotor asymmetries. In this paper, the reduction of wind turbine structural loads caused by rotor asymmetries is discussed. To this aim, suitable transformation of structural loads and control algorithm based on such transformation are proposed. Simulation results show that proposed control algorithm is capable of reducing structural loads caused by rotor asymmetries.