Collective Blade Pitch Research Articles

Structural Load Analysis of a Wind Turbine under Pitch Actuator and Controller Faults

In this paper, we investigate the characteristics of a wind turbine under blade pitch angle and shaft speed sensor faults as well as pitch actuator faults. A land-based NREL 5MW variable speed pitch reg- ulated wind turbine is considered as a reference. The conventional collective blade pitch angle controller strategy with independent pitch actuators control is used for load reduction. The wind turbine class is IEC-BII. The main purpose is to investigate the severity of end effects on structural loads and responses and consequently identify the high-risk components according to the type and amplitude of fault using a servo-aero-elastic simulation code, HAWC2. Both transient and steady state effects of faults are studied. Such information is useful for wind turbine fault detection and identification as well as system reliability analysis. Results show the effects of faults on wind turbine power output and responses. Pitch sensor faults mainly affects the vibration of shaft main bearing, while generator power and aerodynamic thrust are not changed significantly, due to independent pitch actuator control of three blades. Shaft speed sensor faults can seriously affect the generator power and aerodynamic thrust. Pitch actuator faults can result in fully pitching of the blade, and consequently rotor stops due to negative aerodynamic torque.

Non-Linear Aeroelastic Stability of Wind Turbines

As wind turbines increase in magnitude without a proportional increase in stiffness, the risk of dynamic instability is believed to increase. Wind turbines are time dependent systems due to the coupling between degrees of freedom defined in the fixed and moving frames of reference, which may trigger off internal resonances. Further, the rotational speed of the rotor is not constant due to the stochastic turbulence, which may also influence the stability. In this paper, a robust measure of the dynamic stability of wind turbines is suggested, which takes the collective blade pitch control and non-linear aero-elasticity into consideration. The stability of the wind turbine is determined by the maximum Lyapunov exponent of the system, which is operated directly on the non-linear state vector differential equations. Numerical examples show that this approach is robust for stability identification of the wind turbine system.

Performance Measurements of a 1/6-Scale Model of the 1907 Cornu Rotor

Measurements of the performance of an approximate 1/6-scale Cornu 1907 rotor system are discussed. The rotor was tested in hover, both in and out of ground effect, over a range of rotational speeds and collective blade pitch angles. The measurements showed that the rotor had low aerodynamic efficiency, with a maximum attainable figure of merit of only about 0.35 for out of ground effect operating conditions. An analysis of the measurements showed that the performance of this rotor is dominated by relatively high induced losses, with an average induced power factor of over two, mainly because of the use of low-aspect-ratio blades. Extrapolation of the performance polar back to zero thrust with the aid of modified momentum theory suggests that the average profile drag coefficient for the blade sections was of the order of 0.1. However, even with the benefits of a proper airfoil section of lower drag, it is shown that without also using a blade design of higher aspect ratio, the figure of merit of the Cornu rotor design could not be improved much above 0.4. The measured results confirm previous modeling assumptions used for the aerodynamic and performance analysis of the Cornu rotor design and conclusions drawn regarding the unfeasibility of successful free flights of the Cornu helicopter.

Intelligent Control of a Large Variable Speed Wind Turbine

We present two intelligent controllers for large and flexible wind turbines operating in high-speed winds, a Fuzzy-P + I and an adaptive neuro-fuzzy controller. The control objective is to regulate the rotor speed at the given rated power in region 3 (full load) via collective blade pitch angle. The modeled turbine is a three-bladed, upwind machine with a flexible blade and tower. We use the particle swarm optimization method in off-line training for our adaptive neuro-fuzzy controller. Numerical simulations are performed using wind inflow step change with a set of input–output data of a nonlinear wind turbine model. We compare the performance of the proposed controllers with the baseline PI-controller. Simulation results confirm successful performance of the proposed controllers.

LQG Design for Megawatt-Class WECS With DFIG Based on Functional Models' Fidelity Prerequisites

With the increasing trend of connecting high penetrations of wind energy conversion systems (WECSs) to the transmission networks comes the challenge of updating the grid code for the connection of megawatt-class wind turbines. Starting with each WECS entity in the wind farm, the specifications would require the ability to complement some of the power system control services-voltage and frequency control-currently carried out by conventional synchronous generation. This paper investigates output power stability of a WECS in a highly fluctuating wind environment. Based on a performability model, a control strategy is devised for maximizing energy conversion in low to medium winds, and maintaining rated output in above rated winds while keeping torsional torque fluctuations to a minimum. Control is exercised via collective blade pitch control as well as generator torque control. The fundamental philosophy behind the proposed control strategy for the wind turbine coupled to an asynchronous doubly fed induction generator is general and can be easily extended to other WECS configurations.

Controlling Platform Motions and Reducing Blade Loads for Floating Wind Turbines

Offshore sites hold great promise for the growth of wind energy. To tap the vast resource in deep water sites, new support structures, such as those that float, are needed. For floating structures to succeed, they must withstand the offshore wind and wave environment. Two new methods for controlling a floating turbine and reducing the platform and blade loads are presented. The first is a method for controlling collective blade pitch and reducing platform pitch motion, a significant problem for floating structures. The rated generator speed is made a function of the platform pitch velocity. When the platform is pitching upwind, the set point generator speed is set to a larger value, and vice versa. For constant generator torque, this approach essentially makes the rated power a variable that depends on the platform pitch velocity. Fundamentally, this control approach trades power variability for platform pitch variability. The results will show substantial reductions in platform pitch motion but minor increases in power variability. Second, an individual blade pitch controller (IPC) designed to reduce blade fatigue loads is implemented for a floating turbine. The IPC approach is commonly utilized for reducing the 1P fatigue loads on the blades. The goal of implementing this IPC approach is to investigate how traditional load reduction control, which is successful for onshore turbines, integrates and performs with floating turbines. The results will demonstrate the unique challenge of reducing blade loads on a floating turbine.

Full-State Feedback Control of a Variable-Speed Wind Turbine: A Comparison of Periodic and Constant Gains

An investigation of the performance of a model-based periodic gain controller is presented for a two-bladed, variable-speed, horizontal-axis wind turbine. Performance is based on speed regulation using full-span collective blade pitch. The turbine is modeled with five degrees-of-freedom; tower fore-aft bending, nacelle yaw, rotor position, and flapwise bending of each blade. An attempt is made to quantify what model degrees-of-freedom make the system most periodic, using Floquet modal properties. This justifies the inclusion of yaw motion in the model. Optimal control ideas are adopted in the design of both periodic and constant gain full-state feedback controllers, based on a linearized periodic model. Upon comparison, no significant difference in performance is observed between the two types of control in speed regulation.

Month in the Patent Office

An aircraft fitted with fixed wings 14 and a conventional empennage 12, which would be ineffective with the machine hovering or moving forward at very low speed, is rendered stable under such conditions by fitting slotted flaps 15,16 to the wings 14 to deflect downwardly in the direction of the arrows 18, 18 the slipstreams from symmetrically disposed propellers 17 capable of tilting in the pitching plane about axes 21 and located sufficiently forward of the centre of gravity 20 to ensure stability, i.e. by more than 80 per cent of the mean wing chord. In the extreme adjusted positions the propeller thrust lines 23,24 lie above and below the centre of gravity respectively. FIG. 2 shows the disposition of the controls for an aircraft incorporating two pairs of propellers 50, 50b and 62, 62b which are operable conjointly with the normal control surfaces to produce moments augmenting those of the surfaces. Movement of the control column 42 to operate the elevators 45 also effects similar tilting of the inboard propellers 50, 50b in the pitching plane through links 46, 48, 67, 67b, while operation of the wheel 43 controlling the ailerons 56,56b causes a cable loop 58 to rotate a nut 59 to effect differential adjustment of the blade pitches of the outboard propellers 62, 62b. Movement of the rudder pedals 44, 44b results in rotation of a nut 51 by a cable 53 to cause tilting of the inboard propellers 50, 50b in opposite directions. Collective blade pitch adjustment of all four propellers is effected by a hydraulic jack 63. The inboard propellers may be capable of bodily tilting movement, or the blades may be cyclically adjusted in pitch by a swash plate to produce virtual tilting.

A Type of Lifting Rotor with Inherent Stability

The more important of the forward flight aerodynamic characteristics of a rotor type are presented where the collective blade pitch angle is kinematically coupled with the collective flapping or coning angle, while no coupling is provided between cyclic flapping and cyclic pitch angles. The rotor with pitch-cone change may be designed to have positive static stability as compared to the negative static stability of the conventional fixedpitch rotor; partial blade stall during pull-ups or upward gusts may be avoided in spite of a high and economic thrust coefficient in steady flight, and no adjustment of the collective pitch control is required for the transition from powered flight to autorotation. The rotor with pitch-cone change, because of its inherent stability, promises, without recourse to external stabilizing devices, appreciably improved flying qualities of the helicopter.