27,344 research outputs found

    Fault tolerant control design of floating offshore wind turbines

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    This work is concerned with active vibration mitigation in wind turbines (WT) but not through the use of specifically tailored devices. Instead, a general control scheme is designed for torque and pitch controllers based on a super-twisting algorithm, which uses additional feedback of the fore-aft and side-to-side acceleration signals at the top of the WT tower to mitigate the vibrational behavior. In general, proposed methods to improve damping through pitch and torque control suffer from increased blade pitch actuator usage. However, in this work the blade pitch angle is smoothed leading to a decrease of the pitch actuator effort, among other benefits evidenced through numerical experiments. The most frequent faults induce vibrations in the corresponding WT subsystems. In fact, vibration monitoring has been recently used for fault diagnosis Thus, by means of vibration mitigation, different faulty conditions can be alleviated leading to a passive fault tolerant control. In this work, coupled non-linear aero-hydro- servo-elastic simulations of a floating offshore wind turbine are carried out for one of the most common pitch actuator faults.Postprint (published version

    Dual output variable pitch turbofan actuation system

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    An improved actuating mechanism was provided for a gas turbine engine incorporating fan blades of the variable pitch variety, the actuator adapted to rotate the individual fan blades within apertures in an associated fan disc. The actuator included means such as a pair of synchronizing ring gears, one on each side of the blade shanks, and adapted to engage pinions disposed thereon. Means were provided to impart rotation to the ring gears in opposite directions to effect rotation of the blade shanks in response to a predetermined input signal. In the event of system failure, a run-away actuator was prevented by an improved braking device which arrests the mechanism

    Characteristics of hingeless rotors with hub moment feedback controls including experimental rotor frequency response, Volume 1

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    Wind tunnel tests to determine the dynamic characteristics of hingeless rotors with hub moment feedback controls and to acquire experimental hingeless rotor transfer functions are discussed. Rotor transfer functions were calculated from data acquired during open loop frequency response tests. The transfer functions are linear and present the rotor longitudinal and lateral frequency responses to collective pitch, longitudinal cyclic pitch, and lateral cyclic pitch. The theoretical analysis was based on the rigid blade flapping model coupled with appropriate control system and cyclic pitch actuator equations of motion

    Analysis and Control of a Variable-Pitch Quadrotor for Agile Flight

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    Fixed-pitch quadrotors are popular research and hobby platforms largely due to their mechanical simplicity relative to other hovering aircraft. This simplicity, however, places fundamental limits on the achievable actuator bandwidth and the possible flight maneuvers. This paper shows that many of these limitations can be overcome by utilizing variable-pitch propellers on a quadrotor. A detailed analysis of the potential benefits of variable-pitch propellers over fixed-pitch propellers for a quadrotor is presented. This analysis is supported with experimental testing to show that variable-pitch propellers, in addition to allowing for generation of reverse thrust, substantially increase the maximum rate of thrust change. A nonlinear, quaternion-based control algorithm for controlling the quadrotor is also presented with an accompanying trajectory generation method that finds polynomial minimum-time paths based on actuator saturation levels. The control law and trajectory generation algorithms are implemented on a custom variable-pitch quadrotor. Several flight tests are shown, which highlight the benefits of a variable-pitch quadrotor over a standard fixed-pitch quadrotor for performing aggressive and aerobatic maneuvers.National Science Foundation (U.S.) (0645960

    A novel approach to structural load control using intelligent actuators

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    The recent trend towards large multi-MW wind turbines resulted in the role of the control system becoming increasingly important. The extension of the role of the controller to alleviate structural loads has motivated the exploration of novel control strategies, which seek to maximise load reduction by exploiting the blade pitch system. The reduction of blade fatigue loads through individual blade pitch control is one of the examples. A novel approach to reduction of the unbalanced rotor loads by pitch control is presented in this paper. Each blade is equipped with its own actuator,sensors and controller. These local blade control loops operate in isolation without a need of communication with each other. The single blade control approach to regulation of unbalanced rotor loads presented in this paper has an important advantage of being relatively easy to design and tune. Furthermore, it does not affect the operation of the central controller and the latter need not be re-designed when used in conjunction with the single blade controllers. Their performance is assessed using BLADED simulations

    Stroke saturation on a MEMS deformable mirror for woofer-tweeter adaptive optics

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    High-contrast imaging of extrasolar planet candidates around a main-sequence star has recently been realized from the ground using current adaptive optics (AO) systems. Advancing such observations will be a task for the Gemini Planet Imager, an upcoming "extreme" AO instrument. High-order "tweeter" and low-order "woofer" deformable mirrors (DMs) will supply a >90%-Strehl correction, a specialized coronagraph will suppress the stellar flux, and any planets can then be imaged in the "dark hole" region. Residual wavefront error scatters light into the DM-controlled dark hole, making planets difficult to image above the noise. It is crucial in this regard that the high-density tweeter, a micro-electrical mechanical systems (MEMS) DM, have sufficient stroke to deform to the shapes required by atmospheric turbulence. Laboratory experiments were conducted to determine the rate and circumstance of saturation, i.e. stroke insufficiency. A 1024-actuator 1.5-um-stroke MEMS device was empirically tested with software Kolmogorov-turbulence screens of r_0=10-15cm. The MEMS when solitary suffered saturation ~4% of the time. Simulating a woofer DM with ~5-10 actuators across a 5-m primary mitigated MEMS saturation occurrence to a fraction of a percent. While no adjacent actuators were saturated at opposing positions, mid-to-high-spatial-frequency stroke did saturate more frequently than expected, implying that correlations through the influence functions are important. Analytical models underpredict the stroke requirements, so empirical studies are important.Comment: 16 pages, 10 figure

    Hysteresis-based design of dynamic reference trajectories to avoid saturation in controlled wind turbines

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    The main objective of this paper is to design a dynamic reference trajectory based on hysteresis to avoid saturation in controlled wind turbines. Basically, the torque controller and pitch controller set-points are hysteretically manipulated to avoid saturation and drive the system with smooth dynamic changes. Simulation results obtained from a 5MW wind turbine benchmark model show that our proposed strategy has a clear added value with respect to the baseline controller (a well-known and accepted industrial wind turbine controller). Moreover, the proposed strategy has been tested in healthy conditions but also in the presence of a realistic fault where the baseline controller caused saturation to nally conduct to instability.Peer ReviewedPostprint (author's final draft

    Supplementing wind turbine pitch control with a trailing edge flap smart rotor

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    Placement of additional control devices along the span of the wind turbine blades is being considered for multi-MW wind turbines to actively alter the local aerodynamic characteristics of the blades. This smart rotor approach can reduce loads on the rotor due to wind field non-uniformity, but also, as presented in this paper, can supplement the pitch control system. Rotor speed and tower vibration damping are actively controlled using pitch. By supplementing the speed control using smart rotor control, pitch actuator travel is reduced by 15 pitch rates by 23 and pitch accelerations by 42 This is achieved through filtering the pitch demand such that high frequency signals are dealt with by the smart rotor devices while the low frequency signal is dealt with by pitching the blades. It is also shown that this may be achieved while also using the smart rotor control for load reduction, though with reduced effectiveness. This shows that smart rotor control can be used to trade pitch actuator requirements as well as load reductions with the cost of installing and maintaining the distributed devices

    Electromechanical control actuator system Patent

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    Electromechanical control actuator system using double differential screw
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