GB2436599A

GB2436599A - Wind turbine blade furling system

Info

Publication number: GB2436599A
Application number: GB0606357A
Authority: GB
Inventors: David Sharman; Giles Pearson
Original assignee: BOOST ENERGY SYSTEMS Ltd
Current assignee: BOOST ENERGY SYSTEMS Ltd
Priority date: 2006-03-30
Filing date: 2006-03-30
Publication date: 2007-10-03
Also published as: GB0606357D0

Abstract

A blade furling system of a small (less than 20kW output) wind turbine adjusts the "angle of attack" all the blades simultaneously, preferably via a linkwork that comprises a crank pin P which is attached to the blade, and is held in contact with a slider L which is acted on by spring(s) M. The force of the wind on the blades automatically changes the angle of the blades and the amount of change is regulated by the spring force and pitch weights F. Bi-stable and Tri-stable positions of the blades are shown in figures 5a and b. The Tri-stable position is achieved by using two springs M0 and M1.

Description

Page 1 of6 Wind turbine blade furling & power control system This

invention relates to a device for furling the blades of a small wind turbine so as to control the wind power captured.

Wind turbine blades impart force to an electrical generator via a linking drive-train mechanism. If wind turbines are unregulated then in high winds they capture more power than the generator can absorb, and/or more power than the drive-train can transmit.

If the blades are set at the optimum angle of attack to the average wind then they are not at the best angle of attack to commence generation of power in low winds.

In small wind turbines of 20kW electrical power output or less, and with three or more blades, the drive-train and generator can either be over designed in comparison with the blade size so as to cater for the high wind conditions, or alternatively a power control device incorporated into the design. Power control devices include braking mechanisms; aerolastic blades; and furling mechanisms. Mechanical, electrical, hydraulic, and aero-dynamical braking mechanisms suffer from having to absorb energy once it is already in the rotor drive-train as well as the problems associated with mechanisms that either operate when not desired, or which don't operate when required. Aerolastic blades deform in high winds, shedding the wind energy at source but this creates a large amount of acoustical noise in a pattern which nearby humans generally find displeasing as well as fatiguing the blades.

Furling mechanisms are of two varieties: one approach is to turn the entire rotor disc out of the wind (either sideways or vertically, or a combination) and a second approach is to alter the angle of attack of the individual rotor blades (either into or out of the wind).

Furling the rotor disc in any plane leads to large unbalanced forces on the turbine & mounting system, is noisy, is slow to operate, prevents reliable capture of even a portion of the available energy from high winds, and cannot be employed on marine vessels because vessel motions affect correct operation. Altering the angle of attack of the individual blades is termed blade pitch control and the blades can either be turned so as to minimise resistance to the wind by turning them side- on to the wind direction (feathering); or by turning them across the wind direction (stalling).

Blade pitch control mechanisms are better than rotor furling mechanisms because they can be faster to operate; they can enable controlled power production in a regulated manner in even very high winds; they can operate from moving marine platforms such as vessels and buoys; they allow for more compact turbine layouts; they can be quieter in operation; and they can exert symmetrically balanced forces onto the turbine & mounting in general and the drive-train in particular. To maximise these benefits it is highly desirable to pitch all the blades simultaneously so as to minimise unbalanced blade forces and so as to respond as rapidly as possible to fluctuating wind conditions. Existing pitch control mechanisms that operate simultaneously on three or more blades incorporate external governor mechanisms and flyweights which suffer from the disadvantages of increased inertial mass; of increased complexity; from exposing the governor mechanism Page 2 of 6 to the forces of nature with decreased reliability; and requiring careful installation and maintenance by trained personnel with special tools.

To overcome these problems the present invention proposes a wind turbine blade pitch control furling and power control mechanism comprising three or more suitably designed blade assemblies and a linkage mechanism within an appropriately designed hub that transmits power to the electrical generator via a drive train.

An example of the invention will now be described by referring to the accompanying drawings in which: Figure 1 shows the general arrangement of a typical upwind wind turbine Figure 2 shows the general arrangement of a typical downwind wind turbine Figure 3 shows an exploded diagram of a hub and linkage mechanism Figure 4 shows direction of operation of feathering versus stalling Figure 5 shows operation of the springs & slider & blade positions In figure 1 and figure 2 the difference between an upwind and downwind wind turbine is shown. In an upwind wind turbine the blades (A) are upwind of the mounting (B) whilst in a downwind turbine the blades are downwind of the mounting. The direction of the wind's motion is shown by the fletched arrow (C). The present invention will work equally well in both upwind and downwind wind turbines. Both figure 1 and figure 2 illustrate three bladed wind turbines but the present invention will work with three or more blades.

In figure 2 a typical blade assembly (D) is shown as comprising a blade (F) and a blade pitching weight (F). The purpose of the blade pitching weight is to adjust the centre of mass of the blade assembly away from that of the blade itself if the aerodynamic and kinematic considerations result in a centre of mass for the blade which is different than that of the desired location of the centre of mass of the blade assembly as a whole.

In figure 3 an exploded diagram is shown of a typical hub assembly together with a suitable linking mechanism. The figure shows the hub assembly of a three bladed turbine but for clarity only one set of critical parts in the hub and linkage are labelled. Blades are omitted for clarity but the blade pitching weights (F) are shown. Each blade assembly rotates around a pitch axis (G I, G2, G3, etc) which is formed by a restraining mounting provided by the hub (H) and bearings (1 and J) through which the blade shafts (0) drive via cranks (K) onto a slider (E.g) which slides on a shaft (Q). The crank pins (P) are trapped between two flanges on the slider. The slider is forced onto a stop by a pitch control spring (M). The hub back-plate (N) and various seals together form a protective environmental enclosure for the linkage mechanism. The hub assembly forms a rigid rotating frame of reference that constrains the mechanical linkage.

Page 3 ofó The connection of all the blades via their respective shafts and cranks onto a common slider ensures that all the blades move simultaneously and present the same angle of attack to the wind as each other. A balance of forces exists in operation whereby aerodynamic forces on the blades, centrifugal forces on the blade assembly and furling mechanism, and spring forces are in equilibrium and/or against travel limits.

The spring forces can be generated by mechanical springs (illustrated in figure 3), pneumatic springs, and hydraulic springs.

Locating the crank pins (P) between the two flanges of the slider (L) ensures positive linkage of all of the blades to each other. This ensures they will all present the same angle of attack to the wind at the same time. This ensures that there are a minimum of unbalanced forces acting on the blades, hub, linkage mechanism, and alternator drive-train.

The positive linkage of all the blades to each other ensures that the furling mechanism will operate more rapidly than if each blade was to furl individually. This creates a very rapid response to fluctuating wind conditions.

The furling system described is equally applicable to upwind and downwind turbines.

The furling system as described is equally applicable to furling mechanisms which stall the wind turbine blades, or to furling mechanisms which feather the wind turbine blades.

Figure 4A shows the blade of an upwind wind turbine in the normal position (X) and in the stalled position (Y), whilst figure 411 shows the blade of an upwind turbine in the normal position (X) and in the feathered position (Z). The furling system as described is equally applicable to downwind turbines. All that is required is to adjust the centre of mass of the blade assembly and linkage mechanism to drive the blade forwards or backwards against the pitch control spring which can be placed on either side of the slider. The centre of the mass of the blade assembly and linkage can be easily adjusted by either fitting suitable pitch weights (F) on the downwind side of the blades (to stall) or to the upwind side of the blades (to feather); or by sweeping the blades downwind (to stall) or upwind (to feather); or by a combination of both pitch weights and blade sweep. If the blades are swept upwind or downwind then they will describe a rotor cone when rotating rather than a rotor disc.

It is possible to make the system either snap acting (in which it alternates between stable states) or progressive in action by adjusting the balance of the three forces in the system.

The example furling system illustrated in figure 3 has two stable equilibrium positions.

This is illustrated in figure 5A where the slider moves from the normal operating position X I where ills held at rest against the downwind stop to move to the furled (stalled) position X2 where the centrifugal forces overcome the spring and aerodynamic forces.

The span of control of the furling action in wind-speed terms is described by the speed at which the wind-speed first triggers the mechanism and the wind-speed at which the Page 4 of 6 mechanism is continually triggered. In between these lower and upper wind-speeds a snap acting furling system will oscillate from furled to unfurled, and a progressive furling system will smoothly and progressively adjust blade angles towards the limit. Above the upper speed of the span of control the blades will remain continually furled. Selection of appropriately shaped and positioned blade assemblies and linkages will result in stable control solutions.

It is possible to create multiple stable positions and a tn-stable system is illustrated in figure 5B where the slider commences in position XO, then moves to the normal operating position Xl, and finally to the stalled position X2. This is because two concentric furling springs (MO and M I) are incorporated such that the second spring only begins operation in a cumulative manner above the wind-speed associated with the normal operating position Xl. The advantage of this particular arrangement is that the blades can be set for a fine angle of attack at low speeds (position XO) and will therefore initiate movement of the rotor disc and drive-train at lower wind-speeds than if they had been in the normal position Xl. This advantage is important because it is advantageous for the cut-in wind-speed of a wind turbine to be as low as possible in order to maximise generated power. Many multi stable positions can be created in this manner and a variety of spring layouts utilised, including placing springs on both sides, or either side of the slider.

Factory adjustment of the normal angle of attack of the blades can be achieved by inserting a shim at the limit of travel of the slider.

Because there is no separate governor mechanism there is inherently less complexity and therefore less chance of failure and increased reliability.

Because all components can be factory assembled and tested there is increased ease of installation and the installers require no special tools or expertise.

The system is passive in nature and requires no external energy input other than the wind energy.

Claims

Page 5 of6 Claims 1. A small wind turbine (20kW or less output power)

blade furling & power control system comprising three or more suitably designed blade assemblies and a mechanical linkage mechanism within an appropriately designed hub that transmits power to the electrical generator via a drive train.

2. A small wind turbine (20kW or less output power) blade furling & power control system according to claim I, in which simultaneous pitch control of all the blades is obtained by means of a suitable mechanical linkage mechanism 3. A small wind turbine (20kW or less output power) blade furling & power control system according to claim 1, in which environmental protection of the linkage is obtained by means of the external shell of the hub assembly together with the associated seals.

4. A small wind turbine (20kW or less output power) blade furling & power control system according to claim 1, in which the hub provides a rotating rigid rotating frame of reference to contain and support the mechanical linkage.

5. A small wind turbine (20kW or less output power) blade furling & power control system according to claim 1, in which the angle of attack of all blades can be simultaneously adjusted during maintenance or assembly by the insertion of shims in only one location.

6. A small wind turbine (20kW or less output power) blade furling & power control system according to claim 1, in which a variety of stable control solutions can be obtained.

7. A small wind turbine (20kW or less output power) blade furling & power control system according to claim 1, in which either progressive or snap acting control of the blades' angle of attack can be obtained as wind-speed alters.

8. A small wind turbine (20kW or less output power) blade furling & power control system according to claim I, in which all the blades will respond equally to changes in wind speed.

9. A small wind turbine (20kW or less output power) blade furling & power control system according to claim I, in which the angle of attack of the blades can be progressively altered from fine to coarse so as to enable low wind speed starting without compromising higher wind speed performance.

10. A small wind turbine (20kW or less output power) blade furling & power control system according to claim 1, in which wind energy can be regulated before entering the drive-train.

11. A small wind turbine (20kW or less output power) blade furling & power control system according to claim I, in which the span of control of the system can be pre determined.

12. A small wind turbine (20kW or less output power) blade furling & power control system according to claim 1, which requires no special installer or maintainer expertise or training or tools.

13. A small wind turbine (20kW or less output power) blade furling & power control system according to claim I, which is passive in operation and so requires no external energy input other than the wind force.