Method for controlling an offshore floating tower wind turbine, and control system and wind turbine that use the method

Abstract

The invention relates to a control method for controlling an offshore floating tower wind turbine and to various systems and a wind turbine that use said method. The invention is mainly based on the control of the pitch angle of the blades of the wind turbine by means of power levels different from rated power, depending on the movement conditions to which the wind turbine is subjected at sea, and for above rated operating conditions wind speed. Owing to the described method, the invention allows the movements experienced by the wind turbine to be reduced, using the energy performance thereof more efficiently, without detriment to the service life thereof.

Claims

1. A control method for controlling an offshore tower wind turbine, wherein said wind turbine comprises a rotor with a plurality of blades and a plurality of actuators, said control method comprising: a. producing a power P with the wind turbine, that is variable over time and dependent on a relative wind speed V.sub.w at which a wind strikes the rotor, where P.sub.rated is a rated power of the wind turbine that may be achieved when the relative wind speed V.sub.w is equal to or greater than a rated wind speed V.sub.r; b. regulating a pitch angle A of the plurality of blades with the plurality of actuators, such that: i. given the relative wind speed V.sub.w, an increase in the pitch angle A of the plurality of blades entails a decrease in a rotation speed of the rotor and/or of the produced power P and/or of a thrust that the wind exerts on the rotor; ii. given the relative wind speed V.sub.w, a decrease in the pitch angle A of the plurality of blades entails an increase in the rotation speed of the rotor and/or of the produced power P and/or of the thrust that the wind exerts on the rotor; iii. the pitch angle A of the plurality of blades has a minimum value which is assigned, by convention, a 0-degree pitch value for the plurality of blades; iv. given the relative wind speed V.sub.w greater than V.sub.r, there is a theoretical pitch angle of the plurality of blades A.sub.t greater than 0 degrees, such that the produced power P is substantially equal to P.sub.rated; c. experiencing, in at least one working condition, movements that generate a speed of the wind turbine V.sub.a, which is understood as being positive (V.sub.a>0) when the wind turbine is displaced in a direction substantially contrary to the direction of the wind and is understood as being negative (V.sub.a<0) when the wind turbine is displaced in a direction coinciding substantially with the direction of the wind; d. monitoring the speed of the wind turbine V.sub.a directly or indirectly with sensors; establishing at least during part of the time for which the speed of the wind turbine V.sub.a is positive (V.sub.a>0) and the relative wind speed V.sub.w is greater than V.sub.r (V.sub.w>V.sub.r), a pitch angle A of the plurality of blades less than A.sub.t (A<A.sub.t), wherein the wind turbine produces a power P greater than P.sub.rated (P>P.sub.rated); and/or establishing at least during part of the time for which the speed of the wind turbine V.sub.a is negative (V.sub.a<0) and the relative wind speed V.sub.w is greater than V.sub.r (V.sub.w>V.sub.r), a pitch angle A of the plurality of blades greater than A.sub.t (A>A.sub.t), wherein the wind turbine produces a power P less than P.sub.rated (P<P.sub.rated).

2. The control method according to claim 1, wherein a variable P.sub.max is additionally used, where: a. the value of P.sub.max is established dynamically and may therefore vary in each instant; b. P.sub.max is defined as an upper threshold of power P such that, if the relative wind speed V.sub.w and/or the rotation speed of the rotor increase tending to generate a power greater than P.sub.max, action is taken by increasing the pitch angle A of the plurality of blades so as to prevent and/or correct the power in the wind turbine being greater than P.sub.max; and wherein: c. at least during part of the time for which the speed of the wind turbine V.sub.a is positive, variable P.sub.max is assigned a value greater than P.sub.rated, and/or d. at least during part of the time for which the speed of the wind turbine V.sub.a is negative, variable P.sub.max is assigned a value equal to P.sub.rated.

3. The control method according to claim 1, further comprising a step of reducing the pitch angle A of the plurality of blades, wherein a variable P.sub.min is used, where: a. the value of P.sub.min is established dynamically and may therefore vary in each instant; b. P.sub.min is defined as a lower power threshold, wherein if A>0 and the relative wind speed V.sub.w and/or the rotation speed of the rotor decrease, tending to generate a power less than P.sub.min, the pitch angle A of the plurality of blades is reduced so as to maintain and/or increase the power in the wind turbine; and wherein: c. at least during part of the time for which the speed of the wind turbine V.sub.a is positive, variable P.sub.min is assigned a value equal to P.sub.rated; and/or d. at least during part of the time for which the speed of the wind turbine Va is negative, variable P.sub.min is assigned a value less than P.sub.rated.

4. The control method according to claim 1, wherein a variable P.sub.target is used, where: the value of P.sub.target is established dynamically and may therefore vary in each instant; P.sub.target is defined as the target power that the control method seeks to generate in a specific instant by the wind turbine; wherein: the value of the variable P.sub.target is established depending at least on the value of the speed of the wind turbine V.sub.a and wherein: at least during part of the time for which the speed of the wind turbine V.sub.a is positive, variable P.sub.target is assigned a value greater than P.sub.rated; and/or at least during part of the time for which the speed of the wind turbine V.sub.a is negative, variable P.sub.target is assigned a value less than P.sub.rated.

5. The control method according to claim 1, characterized in that the value of the pitch angle A of the plurality of blades is established taking into consideration the value and/or sign of the speed V.sub.a of the wind turbine.

6. The control method according to claim 4, characterized in that the value of the pitch angle A of the plurality of blades is defined in two phases: a. a first phase in which the value of the theoretical pitch angle A.sub.t is calculated; b. a second phase in which a correction is applied on said theoretical pitch value of the plurality of blades to establish a real pitch value to be applied, establishing said correction according to at least one of the following rules: i. if the speed of the wind turbine V.sub.a is positive, a correction is applied on the theoretical pitch value which prevents, reduces, or delays increases in pitch; ii. if the speed of the wind turbine V.sub.a is negative, a correction is applied on the theoretical pitch value which prevents, reduces, or delays decreases in pitch.

7. The control method according to claim 1, characterized in that: e. at least during part of the time for which the speed of the wind turbine V.sub.a is positive (V.sub.a>0) and V.sub.w>V.sub.r, the control method prevents increases in the pitch angle A of the plurality of blades; and/or f. at least during part of the time for which the speed of the wind turbine V.sub.a is negative (V.sub.a<0) and V.sub.w>V.sub.r, the control method prevents decreases in the pitch angle A of the plurality of blades.

8. The control method according to claim 1, characterized in that the steps a-d of the control method are exerted only in the event of movements of the wind turbine having a specific amplitude and/or speed threshold value.

9. The control method according to claim 2, further comprising monitoring a temperature in the wind turbine by means of sensors, and in that the value which variable P.sub.max and/or P.sub.target are assigned in each instant depends on the temperature measured in the wind turbine.

10. The control method according to claim 2, characterized in that the control method comprises monitoring a voltage in the wind turbine by means of sensors, and in that the value which variable P.sub.max and/or P.sub.target are assigned in each instant depends on the voltage measured in the wind turbine.

11. The control method according to claim 10, characterized in that the control method is used in a wind turbine supported by a flexible and non-floating substructure, wherein the wind turbine comprises a first oscillation mode which has a period equal to or greater than 3 seconds.

12. A control system for controlling an offshore tower wind turbine, said wind turbine comprising a rotor with a plurality of blades and a plurality of actuators, the control system comprising: one or more monitoring sensors for monitoring a plurality of physical parameters of said wind turbine; and a controller adapted to adjust a power P with the wind turbine and a pitch angle A of the plurality of blades, wherein the wind turbine, the monitoring sensors and the controller are configured to carry out the following steps: a. producing the power P with the wind turbine, wherein P is variable over time and dependent on a relative wind speed V.sub.w at which a wind strikes the rotor, where P.sub.rated is a rated power of the wind turbine that may be achieved when the relative wind speed V.sub.w is equal to or greater than a rated wind speed V.sub.r; b. regulating the pitch angle A of the plurality of blades with the plurality of actuators and the controller, such that: i. given the relative wind speed V.sub.w, an increase in the pitch angle A of the plurality of blades entails a decrease in a rotation speed of the rotor and/or of the produced power P and/or of a thrust that the wind exerts on the rotor; ii. given the relative wind speed V.sub.w, a decrease in the pitch angle A of the plurality of blades entails an increase in the rotation speed of the rotor and/or of the produced power P and/or of the thrust that the wind exerts on the rotor; iii. the pitch angle A of the plurality of blades has a minimum value which is assigned, by convention, a 0-degree pitch value for the plurality of blades; iv. given the relative wind speed V.sub.w greater than V.sub.r, there is a theoretical pitch angle of the plurality of blades A.sub.t greater than 0 degrees, such that the produced power P is substantially equal to P.sub.rated; c. experiencing, in at least one working condition, that generate a speed of the wind turbine V.sub.a, which is understood as being positive (V.sub.a>0) when the wind turbine is displaced in a direction substantially contrary to the direction of the wind and is understood as being negative (V.sub.a<0) when the wind turbine is displaced in a direction coinciding substantially with the direction of the wind; d. monitoring the speed of the wind turbine V.sub.a directly or indirectly with the monitoring sensors; establishing at least during part of the time for which the speed of the wind turbine V.sub.a is positive (V.sub.a>0) and the relative wind speed V.sub.w is greater than V.sub.r (V.sub.w>V.sub.r), a pitch angle A of the plurality of blades less than A.sub.t (A<A.sub.t), wherein the wind turbine produces a power P greater than P.sub.rated (P>P.sub.rated); and/or establishing at least during part of the time for which the speed of the wind turbine V.sub.a is negative (V.sub.a<0) and the relative wind speed V.sub.w is greater than V.sub.r (V.sub.w>V.sub.r), a pitch angle A of the plurality of blades greater than A.sub.t (A>A.sub.t), wherein the wind turbine produces a power P less than P.sub.rated (P<P.sub.rated).

13. A wind turbine comprising the control system of claim 12.

14. The wind turbine according to claim 13, further comprising an electrical system capable of temporarily producing a power P greater than its rated power P.sub.rated, in intermittent periods having a duration of less than 100 seconds and intercalated with periods in which a power P less than P.sub.rated is produced.

Description

DESCRIPTION OF THE DRAWINGS

(1) The preceding and other features and advantages will become more apparent from the detailed description of the invention, as well as from the preferred embodiments referred to in the attached drawings, in which:

(2) FIGS. 1A-1B show a representation of the pitch angle A of a wind turbine blade.

(3) FIGS. 2A-2C show a variation of graphs for the following magnitudes depending on the wind speed V.sub.w with a conventional controller: a) power P vs. wind speed V.sub.w; b) pitch angle A of the blade vs. wind speed V.sub.w; c) thrust T vs. wind speed V.sub.w.

(4) FIGS. 3A-3B show two representations of the speed of the wind turbine V.sub.a as a result of the movements of the floating structure supporting it.

(5) FIGS. 4A-4B show graphs corresponding to the forward movement cycle (V.sub.a>0) and backward movement cycle (V.sub.a<0), respectively, and how said cycles affect the apparent speed V.sub.w incident on the rotor, compared to a situation in which the wind turbine remains substantially fixed.

(6) FIGS. 5A-5D represent a series of graphs showing how different variables or parameters for the operation or control of a wind turbine evolve over time, and how some of said parameters differ in the case of a fixed wind turbine or one with a conventional controller, and in the case of using the method of the invention.

(7) FIGS. 6A-6C show a variation of graphs for the following magnitudes depending on the wind speed V.sub.w, in a first embodiment of the invention: a) power P vs. wind speed V.sub.w; b) pitch angle A of the blade vs. wind speed V.sub.w; c) thrust T vs. wind speed V.sub.w.

(8) FIGS. 7A-7C show a variation of graphs for the following magnitudes depending on the wind speed V.sub.w, in a second embodiment of the invention with variables P.sub.max and P.sub.min: a) power P vs. wind speed V.sub.w; b) pitch angle A of the blade vs. wind speed V.sub.w; c) thrust T vs. wind speed V.sub.w.

(9) FIGS. 8A-8B show flow charts of the method of the invention, according to a preferred embodiment thereof.

LIST OF REFERENCE NUMBERS IN THE FIGURES

(10) TABLE-US-00001 (1) Wind turbine (2) Rotor (3) Blade (4) Substructure

DETAILED DESCRIPTION OF THE INVENTION

(11) A detailed description of the invention is provided in reference to different preferred embodiments thereof, according to the information provided by FIGS. 1A-8B herein. Said description is provided for illustrative and non-limiting purposes of the claimed invention.

(12) FIGS. 1A-1B schematically show the manner in which the pitch angle (A) of a blade (3) can be varied. FIG. 1A shows a minimum pitch angle (A=0) situation which maximizes exposure of the blades (3) to the wind, and therefore the production capacity of the wind turbine (1), whereas FIG. 1B shows a maximum pitch angle (A=about 90 degrees) situation, which situates the blades (3) in a feathered position and minimizes their exposure to the wind (also see the definition of pitch angle A of the blade (3) included in preceding sections).

(13) To vary the pitch angle (A) of a blade, a wind turbine (1) comprises regulation means, usually consisting of a series of bearings and hydraulic actuators (not shown in FIGS. 1A-1B) controlled by means of the control system for controlling the wind turbine (1).

(14) FIGS. 2A-2C shows a series of 3 curves describing the behavior of a conventional controller or control method, such as those that are normally used for wind turbines operating on fixed structures. FIGS. 3A-3B respectively show how the power (P), pitch angle (A) of the blades, and the horizontal thrust (T) that the wind exerts on the rotor (2) vary, depending on wind speed (Vw).

(15) For low wind speeds, less than a reference value Vr referred to as rated wind speed, the minimum pitch angle A of the blade (A=0) is maintained to maximize production (see FIG. 2B). In said situation, the generated power will be less than the rated power P.sub.rated as wind speed Vw is less than Vr (see FIG. 2A).

(16) When the wind speed reaches value Vr, the wind turbine (1) can start to produce at its rated power. When wind speed Vw exceeds Vr (Vw>Vr), the control system for controlling the wind turbine (1) increases the pitch angle A of the blades (3), as a result of which the production power P is caused not to exceed P.sub.rated (see FIGS. 2A-2B).

(17) Therefore, a certain theoretical value At of the pitch angle of the blade (At>0) corresponds to each wind speed Vw>Vr, such that the produced power P will be equal to the rated power P.sub.rated. Said value may depend on a number of factors, including among them air density at each site. The graph showing the values of At is shown in graph 2b. For example, for a wind speed Vw1>Vr, the theoretical value At1 of the pitch angle of the blades (3) will lead to a production power P equal to the rated power of the wind turbine (1) (P=P.sub.rated).

(18) The horizontal thrust T that the wind exerts on the rotor (2) increases with wind speed while Vw<Vr (slope of the positive curve; see FIG. 2C). However, when Vw>Vr and the pitch starts to act, the situation is inverted and a higher wind speed Vw leads to lower thrust T (slope of the negative curve; see FIG. 2C). This latter situation leads to the negative damping phenomenon in situations with Vw>Vr, already described in the background section earlier.

(19) Operation with Vw>Vr is referred to as above rated operation, whereas operation with Vw<Vr is referred to as below rated operation. The value of Vr may vary depending on the wind turbine model (1). Common values for Vr are about 12 m/s.

(20) FIGS. 3A-3B schematically show the possible movements a wind turbine (1), in this case supported by a floating substructure (4), which generally enhances said movements, may experiment. FIG. 3A shows a movement substantially contrary to the direction of the wind (Va>0), whereas FIG. 3B shows a movement coinciding substantially with the direction of the wind (Va<0). Said movements and/or speeds will fundamentally be caused by changes in the inclination of the floating substructure (4), although they may also be caused, at least in part, by horizontal displacements of the substructure (4) or deformations experienced by the substructure (4), for example.

(21) FIG. 3A shows by way of example a floating substructure (4) formed by two bodies, but the present invention applies to wind turbines supported by other types of substructures.

(22) The control method according to the present invention provides a considerable advantage for wind turbines experimenting significant movements, and for that reason it is particularly suitable for floating wind turbines. However, it may also be advantageously used in wind turbines installed on other highly mobile and/or highly flexible substructures without departing from the scope of the invention. For example, the control system according to the present invention can also be used for wind turbines installed on very flexible towers the deformations of which generate significant movements in the wind turbine (1). What is usually known as soft towers, for example, are towers having a high natural oscillation period (higher than the rotation period of the rotor (2)) usually exceeding values of 3 s, which entails associated relevant deformations the negative effects of which may be prevented or mitigated by means of the present invention.

(23) Movements experienced by the wind turbine (1) are generally cyclical, such that movement cycles with Va>0, herein referred to as forward movement cycles, are intercalated with movement cycles with Va<0, herein referred to as backward movement cycles. This is schematically shown in FIG. 4B, where it can be seen how the speed Va of the wind turbine (1) evolves over time and how the forward movement and backward movement cycles will generally be intercalated with one another.

(24) FIG. 4A shows how the wind speed Vw is affected with the movements of the wind turbine (1). The red curve in the graph of FIG. 4A shows how absolute wind speed, subject to natural turbulence or variability, evolves over time; said red curve represents what would be the wind speed Vw in the case of a perfectly fixed wind turbine (1). In turn, the green curve in the same graph represents the apparent or relative wind speed Vw with respect to the rotor (2), when the latter is not fixed but rather moves with speeds Va such as those shown in FIG. 4B. During a backward movement cycle (Va<0), the apparent or relative wind speed Vw decreases with respect to the absolute wind speed, whereas during a forward movement cycle (Va>0), the apparent or relative wind speed Vw increases with respect to the absolute wind speed shown in the red graph.

(25) When looking at the graph in FIG. 4B, it can be considered that when the curve for the speed Va of the wind turbine (1) crosses the x-axis, a new forward movement or backward movement cycle is started. The wind speed Vwi measured in the instant in which a specific cycle i is started (see FIGS. 4A-4B) can be a parameter to be used in the algorithms which control the control method according to the present invention, as will be explained below.

(26) FIGS. 5A-5D represent a series of graphs showing how different variables or parameters of the operation or control of a wind turbine (1) evolve over time. For a better explanation and understanding of the present invention, the representative behavior of a conventional controller with a fixed wind turbine (1) is depicted on one hand using red curves, and the representative behavior of a controller or control method according to the present invention for a floating wind turbine (1) that experiments movements is depicted on the other hand using green curves. The graphs correspond to a situation of above rated operation (Vw>Vr) and show the evolution of different magnitudes over time. The x-axes of all the graphs represent the same period of time on the same scale.

(27) FIGS. 5A-5B are similar to FIGS. 4A-4B, but in the case of FIGS. 5A-5B, it has been assumed in a simplified manner that absolute wind speed is constant over time for the purpose of making the explanation and the graphic depiction thereof simpler. Therefore, the graph of FIG. 5A shows with a red horizontal curve the absolute wind speed, which is what would affect a perfectly fixed wind turbine (1) and in this case has a constant value and is equal to Vw1. In turn, the green discontinuous curve in the same graph shows the wind speed Vw that applies to a moving wind turbine (1), according to the curve of the speed of the wind turbine (1) shown in FIG. 5B. The corresponding intercalated forward movement and backward movement cycles can be observed.

(28) To eliminate or reduce the effect of negative damping and/or the movements experienced by the wind turbine (1), and/or to expand or improve the positive damping of said movements, and/or to increase energy production in the wind turbine (1), the control method according to the present invention carries out an operation (for the conditions of wind speed and wind turbine (1) shown in FIGS. 5A-5B) as depicted in FIGS. 5C-5D.

(29) FIG. 5D shows the pitch angle of the blades A, over time. The horizontal red line represents the case of a fixed wind turbine (1) which, for a wind speed Vw1>Vr, would adopt a theoretical value At1 of the pitch angle of the blades, according to a curve like the one shown in FIG. 2B. The theoretical value At1 is what leads to a power P equal to the rated power P.sub.rated for said wind speed Vw1. Said power that is constant and equal to P.sub.rated which would be what is present in a fixed wind turbine (1) with a conventional controller is represented by the horizontal red line of FIG. 5C.

(30) However, since movements in the wind turbine (1) occur, the speed Vw varies as shown with the green curve in FIG. 5A. A conventional controller would apply a theoretical pitch angle of the blades (3) against said variation in Vw that allowed keeping the produced power approximately constant and equal to P.sub.rated. Said theoretical values At are obtained from a graph such as the one shown in FIG. 2B, and their variation over time, linked to the variation in Vw, is shown with the dotted black curve represented in FIG. 5D. Using said values At for the pitch of the blade (3) would allow keeping the power approximately constant and equal to the rated power, but it would lead to the undesirable negative damping effect described in sections above. To prevent or reduce said negative damping effect, the control method according to the present invention would adopt values for the pitch angle A of the blades (3) such as those represented by means of the discontinuous green curve in FIG. 5D. As can be seen in said curve, said values are such that A (discontinuous green curve) is less than At (dotted black curve) (A<At) during the forward movement cycles (Va>0). Otherwise, in the backward movement cycles A>At.

(31) In turn, the power resulting from the wind turbine (1) is represented in the discontinuous green curve of FIG. 5C: during forward movement cycles (Va>0), the power P produced by the wind turbine (1) will be greater than P.sub.rated, whereas during the backward movement cycles (Va<0), the power P produced will be less than P.sub.rated.

(32) It should be indicated that although the rated power P.sub.rated is generally a fixed and constant value over the service life of a wind turbine, in certain cases or wind turbine models it may be possible to adjust the value thereof for certain operating conditions or depending on certain parameters, e.g., the voltage of the generator, the reactive power to be produced as required by the network system, or the room temperature and/or the generator temperature. Therefore, in one embodiment of the invention, under specific conditions, it is possible to use a corrected value for parameter P.sub.rated that may differ from the rated power listed in the technical data sheet of a specific wind turbine model, without this affecting the operating steps and rules characterizing the method according to the present invention and therefore being kept within the scope thereof.

(33) It must be understood that there are widely varying possibilities or strategies for the control algorithms of a method according to the invention. For example, algorithms which fix a target power value P.sub.target can be used, and the value of A that is established or results in each instant can be derived from said target power, or else specific values of A can be established, and the power values can be those resulting from the values of A that may be fixed. Several other possibilities that are evident or known in the art are likewise possible.

(34) As observed in FIG. 5C, the controller or control method according to the present invention generates brief and intermittent over-production phases (P>P.sub.rated) intercalated with as many other under-production periods (P<P.sub.rated). Compared to the equivalent production situation of a fixed wind turbine (1) (represented by the red line in FIG. 5C), there is an alternating occurrence of periods in which more energy is comparatively generated (areas shaded in green in FIG. 5C corresponding to forward movement cycles) and periods in which less energy is comparatively generated (areas shaded in red in FIG. 5C corresponding to backward movement cycles). In the overall computation, under-production periods are offset by over-production periods to prevent or reduce possible energy losses. The control method according to the present invention can even lead to an increase in energy production as the over-production is greater than the under-production. This may be due to the fact that generated energy is proportional to the cube of wind speed Vw. This means that with the same variation in Vw for a forward movement cycle and a backward movement cycle, the gain in the former is greater than the loss in the latter. For example, if Vw increases by 10% during the forward movement cycle and likewise decreases by 10% during the backward movement cycle, then 1.1{circumflex over ()}3+0.9{circumflex over ()}3=1,331+0.729=2.06>2, whereby more energy is generated than by working at a constant power. The control method according to the present invention thereby provides a manner in which a fraction of the energy associated with the movement of the structure can be extracted by the wind turbine (1).

(35) The cyclic and alternating variation of power is a key factor in the control method according to the present invention. In fact, keeping power greater than P.sub.rated for permanent or prolonged periods may generally not be admissible due to limitations of the generator and/or of other components. In contrast, when over-production periods associated with forward movement cycles are brief and intercalated with under-production periods associated with backward movement cycles, the application and demand on the generator or other components of the electrical system decreases and is similar to what may occur in a situation of production at a power approximately constant and equal to the rated power P.sub.rated.

(36) Furthermore, the shorter duration of the forward movement and/or backward movement cycles, which will typically last for several seconds or tenths of a second, can limit the expected power increases and decreases, because the rotor (2) has a high rotational inertia, and a certain time is therefore required for greater torque of the wind on the rotor (2) to increase the rotation speed thereof, or for a lower torque of the wind to decrease the rotation speed thereof. Taking this into account, in a preferred embodiment of the present invention, the power P generated above rated, is at least in part adjusted by varying the rotation speed of the rotor (2). The increase in power associated with the forward movement cycles is thereby decreased and/or delayed, as it takes time to impart to the rotor (2) the increase in angular momentum associated with a higher rotation speed, and the decrease in power in the backward movement cycles is similarly decreased and/or delayed, as the decrease in torque generated by the wind takes time to translate into the corresponding decrease in rotation speed of the rotor (2) due to the high rotational inertia of the mass of the rotor (2).

(37) Using the rotation speed of the rotor (2) as a parameter for adapting the power in the generator, by involving the rotational inertia of the rotor (2) and representing changes in the angular momentum thereof which require certain time, will lead to the amplitude of the power oscillations in the above rated operation (see FIG. 5C) being lower, thereby generating a potentially favorable effect. It is also for this to cause a certain difference between power oscillations and Va oscillations, which may temporarily involve in the initial part of a forward movement cycle P<P.sub.rated and/or in the initial part of a backward movement cycle P>P.sub.rated, without departing from the scope of the present invention.

(38) The power adjustment according to the present invention can also be done by varying the torque of the generator, or by means of a combination of varying the torque and the rotation speed of the rotor.

(39) There are various specific strategies to establish the values of the pitch angle A of the blades (3) to be used without departing from the scope of the invention. By way of example, FIG. 5D shows various cases: In cycles 1 and 2, a strategy is applied in which the pitch angle A of the blades is kept constant despite variations in Vw. In cycles 3 and 4, the pitch angle A is kept constant until reaching a power threshold after which it starts to vary. In cycle 5, a gradual variation of A is applied throughout the cycle.

(40) Whatever the specific strategy used to establish the exact value of A, the control method according to the present invention will always establish values A<At at least during part of the time for which Va>0 (forward movement cycles), generally coinciding with over-production periods (P>P.sub.rated) and will always establish values A>At at least during part of the time for which Va<0 (backward movement cycles), generally coinciding with under-production periods (P<P.sub.rated).

(41) By preventing or lessening the increases in A during a forward movement cycle, the control method prevents or limits possible decreases in the thrusting force of the wind which resist movement during a forward movement cycle. Likewise, by preventing or lessening the decreases in A during a backward movement cycle, the control method prevents or limits possible increases in the thrusting force of the wind which amplify movement during a forward movement cycle. In that sense, the control method according to the present invention limits or eliminates the unfavorable negative damping effect, and it may even generate in its place positive damping during above rated operation, similarly to what generally occurs during below rated operation.

(42) By way of non-limiting example, FIG. 6A-6C depicts a first embodiment of the control method according to the present invention. FIG. 6B specifically shows the values of the pitch angle of the blades (3) to be adopted during a specific cycle, whether it is the forward movement or the backward movement cycle, and in a situation of above rated operation. The graph of FIG. 5B shows the following curves: Red curve, showing the values of A depending on Vw that a conventional controller would adopt. Said curve indicates the theoretical values At of the pitch angle of the blade (3) which, for each wind speed Vw>Vr, lead to a power P equal to the rated power P.sub.rated. Green curve, corresponding to the values of the pitch angle A of the blades that one embodiment of the control method according to the present invention would establish for a forward movement cycle (Va>0). It can be observed that the values of A indicated by said green curve are always equal to or less than At. Blue curve, corresponding to the values of the pitch angle A of the blades that one embodiment of the control method according to the present invention would establish for a backward movement cycle (Va<0). It can be observed that the values of A indicated by said green curve are always equal to or greater than At.

(43) The green and blue curves correspond to a specific forward movement or backward movement cycle, in which the wind speed Vw had a value Vwi at the start of the cycle (see FIGS. 4A-4B). The curves for cycles that were started at another speed would therefore be different but similar.

(44) The method can establish target values of A, according to the rules of the method described above, such that the value of P is obtained as a result, or it can establish target values of P (by means of the variable P.sub.target), such that the value of A is obtained as a result. Other similar or equivalent strategies may be possible for implementing the method of the invention generating a behavior such as the one depicted in FIGS. 5A-5D and/or FIG. 6A-6C.

(45) Although the theoretical explanation of the control method according to the present invention relates to the wind speed Vw as a possible control parameter, in the practical application of the method it may generally be simpler and more efficient to use another parameter related directly to Vw but simpler to measure and monitor, such as the speed of the rotor (2) or the generator, as is typical in conventional controllers. Similarly, in the practical application of a preferred embodiment of the control method according to the present invention, the value of Va will not be measured directly, but rather will be obtained indirectly from measurements of other related parameters, particularly such as inclination and/or acceleration in the wind turbine (1). Generally, the control method according to the following invention can be used by using other control parameters which are directly related to the parameters used in the description of the method without departing from the scope of the invention. For example, instead of speed Va, the angular speed of the floating structure which is obtained from the rate of variation of the inclination, which is equivalent, can be used as a control parameter, or instead of wind speed, rotor speed, which is directly related, can be used for a torque value in the known generator.

(46) As explained, the speed Va will be generated by the changes in the inclination of the floating support structure, which is generally the most influential parameter, as well as by other parameters such as, for example, horizontal displacements of the floating support structure or deformation of the floating support structure, which will generally be less influential parameters. In a preferred embodiment of the method according to the present invention, the speed Va is determined in an approximate manner only from variations in the inclination of the structure, without taking in consideration, for example, horizontal displacements of the structure. This allows the method according to the present invention to be particularly effective in damping and/or decreasing movements due to inclinations of the structure, which are generally the most relevant movements. Naturally, embodiments which determine Va from other parameters in addition to or instead of inclination of the structure are also possible, without departing from the scope of the invention.

(47) FIG. 6A shows what the power produced by the wind turbine (1) will be in a forward movement cycle (green curve) or of backward movement cycle (blue curve) corresponding with the variation curves of the pitch angle A shown in FIG. 6B, both for above rated operating conditions. It can be seen that PP.sub.rated in the forward movement cycle and PP.sub.rated in the backward movement cycle.

(48) Similarly, the graph shown in FIG. 6C shows what the variation in thrust T exerted by the wind on the rotor (2) will be, depending on the speed of the acting wind by applying the method in a forward movement cycle (green curve) or in a backward movement cycle (blue curve). As can be observed in the green curve, for a forward movement cycle thrust T is always increased compared to the value for the cycle starting speed Vwi. At the same time, as can be observed in the blue curve, for a backward movement cycle thrust T always decreases compared to the value for the cycle starting speed Vwi. Variations in T which resist movement (increasing T in forward movement cycles and decreasing T in backward movement cycles) are thereby achieved, a favorable positive damping thereby being achieved.

(49) FIG. 6C represents the slope S of the curves defining T when Vw>Vwi (in forward movement cycles) and when Vw<Vwi (in backward movement cycles). Said slope will be a function of the curves defining A and/or defining P used in the method (such as those shown in FIGS. 6B and/or 6A). When said slope S is positive (as in the embodiment of the method shown in FIG. 6C), the method allows generating a suitable positive damping even for above rated operation in the same way as in the below rated operation in which the slope of the curve (red curve for Vw<Vr) is notably positive. If another embodiment of the present method generates a negative slope S, positive damping will not be generated, but since said negative slope is less pronounced than that of the red curve for the same value of Vw, the unfavorable negative damping effect will be reduced at least in part.

(50) FIGS. 7A-7C show figures similar to those of FIG. 6A-6C for a second embodiment of the control method according to the present invention, again for above rated operating conditions (Vw>Vr). In this case, the control method incorporates variable P.sub.max, which establishes the power threshold after which values of A which prevent exceeding said upper threshold are established, and variable P.sub.min, which establishes the lower power value after which values of A which prevent a power less than said lower threshold are established.

(51) The control method according to the present invention envisages said variables P.sub.max and P.sub.min having variable values which will be established dynamically and/or in time real taking into account various parameters or circumstances, such as: The type of forward movement or backward movement cycle the wind turbine (1) is in, or in other words, the sign of Va. The temperature of the generator. The voltage of the generator. The value of the wind speed Vwi at the start of the forward movement or backward movement cycle the wind turbine (1) is in.

(52) As can be seen in FIG. 7A, in this embodiment of the method, PP.sub.rated in a forward movement cycle (green curve), but to limit the excess power and/or production, an upper threshold P.sub.max>P.sub.rated is established. Likewise, a lower threshold P.sub.min=P.sub.rated is established in the forward movement cycle (said lower threshold P.sub.min is also established in the embodiment shown in FIGS. 6A-6C).

(53) As can also be seen in FIG. 7A, in this embodiment of the method, PP.sub.rated in a backward movement cycle (blue curve), but to limit the power and/or production loss, a lower threshold P.sub.min<P.sub.rated is established. Likewise, an upper threshold P.sub.max=P.sub.rated is established in the backward movement cycle (said upper threshold is also established in the embodiment shown in FIGS. 6A-6C).

(54) Lastly, FIGS. 8A-8B show flow charts corresponding to the control algorithms used in the embodiment of the method according to the present invention shown in FIG. 7A-7C. On one hand, FIG. 8A shows the flow chart used according to the current state of the art in a conventional controller; said flow chart would result in behavior curves such as those represented in FIGS. 2A-2C and in the red curves of FIGS. 7A-7C. According to said conventional controller, during the above rated operation (Vw>Vr), a power is kept approximately constant and equal to P.sub.rated, regardless of the movements experimented by the wind turbine (1).

(55) In such a conventional controller, the thresholds P.sub.max and P.sub.min described above are also present and/or implicit, adapting an equal and constant value (P.sub.max=P.sub.min=P.sub.rated) regardless of the direction of movement of the wind turbine (1) (i.e., of the sign of Va).

(56) Although a conventional controller according to the state of the art is generally designed to prevent the wind turbine (1) from operating at a power greater than the rated power, this does not necessarily mean that powers greater than the rated power will not arise at some point; however, the possible situations of working at a power greater than the rated power that may arise with controllers known in the art are completely different in form, cause and/or motivation with respect to situations of over-production caused intentionally by means of the control method according to the invention; for example, with a conventional controller a situation with P>P.sub.rated may arise due to the capacity of adjusting the pitch of the blades (3) not being instantaneous, and therefore in the event of a sudden rise in wind speed, there may be an increase in the power produced during the brief interval of time required by the control system to react and adjust the pitch of the blades (3), the purpose of which is to correct said situation. This situation is obviously completely different from what characterizes the control method referred to by the present invention, wherein the moments in which P>P.sub.rated are expected and caused by the control algorithm itself and are dependent on the movements experimented by the wind turbine, as described in FIG. 8B, for example.

(57) FIG. 8B shows the flow chart for a control algorithm of a method according to the present invention. By means of said algorithm, for the above rated operation, the sign of the speed of the wind turbine (1) Va is taken into account to establish the pitch angle A and the variables P.sub.max and P.sub.min as indicated in a self-explanatory manner in the figure.

(58) A control method according to the invention that considers the sign of Va has been described. It is of course possible to develop another embodiment of a method according to the invention which further takes into account the value of Va. For example, the value of Va can be used to establish a variable P.sub.target as described above. Or, for example, a method which maintains conventional algorithms can be used as long as the absolute value of Va does not exceed a certain value or threshold, and it only applies the most advanced method according to the present invention for high speeds of the wind turbine (1), above a certain threshold. Therefore, a conventional method can be maintained as long as speeds Va are small and insufficient to generate a significant negative damping effect.

(59) The positive aerodynamic damping effect provided by the control method according to the present invention can be increased by establishing decreases of A for forward movement cycles (Va>0) and/or establishing increases of A for backward movement cycles (Va<0). One way to implement said improved damping in a control algorithm according to the present invention may consist of establishing P.sub.min>P.sub.rated in forward movement cycles and/or P.sub.max<P.sub.rated in backward movement cycles.