16 research outputs found

    Optimal Shutdown Management

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    The paper presents a novel approach for the synthesis of the open-loop pitch profile during emergency shutdowns. The problem is of interest in the design of wind turbines, as such maneuvers often generate design driving loads on some of the machine components. The pitch profile synthesis is formulated as a constrained optimal control problem, solved numerically using a direct single shooting approach. A cost function expressing a compromise between load reduction and rotor overspeed is minimized with respect to the unknown blade pitch profile. Constraints may include a load reduction not-to-exceed the next dominating loads, a not-to-be-exceeded maximum rotor speed, and a maximum achievable blade pitch rate. Cost function and constraints are computed over a possibly large number of operating conditions, defined so as to cover as well as possible the operating situations encountered in the lifetime of the machine. All such conditions are simulated by using a high-fidelity aeroservoelastic model of the wind turbine, ensuring the accuracy of the evaluation of all relevant parameters. The paper demonstrates the capabilities of the novel proposed formulation, by optimizing the pitch profile of a multi-MW wind turbine. Results show that the procedure can reliably identify optimal pitch profiles that reduce design-driving loads, in a fully automated way

    Cyclic Pitch Control for the Reduction of Ultimate Loads on Wind Turbines

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    In this paper we study the use of individual blade pitch control as a way to reduce ultimate loads. This load alleviation strategy exploits the fact that cyclic pitching of the blades induces in general a reduction of the average loading of a wind turbine, at least for some components as the main bearing, the yaw bearing, or the tower. When ultimate loads are generated during shutdowns, the effect of the use of cyclic pitch results in reduced peak loads. In fact, as the machine starts from a less stressed condition, the response to an extreme gust or other event will result in reduced loading on its components. This form of load mitigation can be seen as a preventative load mitigation strategy: the effect on load reduction is obtained without the need to detect and react to an extreme event, but by simply unloading the machine so that, in case an extreme event happens, the result will be less severe. The effect of peak load mitigation by preventative cyclic pitch is investigated with reference to a multi-MW wind turbine, by using high-fidelity aeroelastic simulations in a variety of operating conditions

    Introduction to Flight Dynamics

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    This book is intended to serve a diverse audience of students, scientists and engineers who are interested in understanding and utilizing the concepts of flight dynamics. The following notes provide to the reader the basic principles based on a classical analytical approach. The concepts of controllability and maneuverability are detailed starting from the definition of stability and control of the equilibrium states. Equations for the estimation of hinge moments and stick force in steady and maneuvering flight are provided. The equations of motion are then extended to unsteady flight and a detailed analytical model is derived for dynamic stability analysis, including an interpretation of stability and control derivatives. Modal response of the vehicle in the longitudinal and lateral-directional plane is also reconstructed. The problems inherent to the evaluation of the flying qualities of a fixed-wing aircraft and the elements of parameter identification are also introduced. Finally, open and closed loop response to controls is discussed both in time and frequency domain

    Trimming a High-Fidelity Multibody Helicopter Model for Performance and Control Analysis

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    This paper brings forward the study of the dynamic behaviour of a novel lightweight helicopter featuring an innovative gimballed two-bladed main rotor. First, previous results for the isolated main rotor are extended for the case of free-coning under cyclic pitch perturbations and longitudinal gusts. Subsequently, the complete helicopter is modelled and a simple control system is derived and applied to steer the helicopter to steady hover and straight flight conditions, showing good characteristics also under gust perturbations

    Power Curve Tracking in the Presence of a Tip Speed Constraint

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    This paper considers the problem of power regulation for a variable speed wind turbine in the presence of a blade tip speed constraint, for example to limit noise emissions. The main contribution of the paper is the formulation of a policy for the regulation of the machine in the transition region between the classical regions II and III that accommodates the tip speed constraint, and the derivation of associated wind schedules for the rotor speed, blade pitch and aerodynamic torque. To exemplify the possible use of such wind schedules in the design of control laws, model-based controllers are formulated in this paper that are capable of performing power curve tracking throughout all wind speeds, in contrast with commonly adopted approaches that use switching controllers to cover the various operating regimes of the machine. The proposed regulation policies and control laws are demonstrated in a high fidelity simulation environment for a representative 3 MW machine
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