FR3152486A1 - Set comprising a floating structure, a wind turbine and means of motorizing it - Google Patents

Abstract

The invention relates to a floating assembly (1) for producing electrical energy comprising a floating structure (10) connected to a buoy (20) using at least one flexible connection (30), means (40) connected to the buoy (20) for anchoring said floating structure (10) to a seabed (5), a wind turbine (100) comprising a supporting structure (110) supporting a propeller (120) rotating about an axis of rotation (XX'), and means (60; 70) for determining at least one of the following parameters among the wind direction, the wind speed, the direction of the sea current and the speed of the sea current, characterized in that it further comprises means (128) for motorizing the propeller (120) in order to rotate its rotor (126) in one direction of rotation or in the opposite direction, means (50) for measuring the separation distance D between the floating structure (10) and a vertical rotation axis (ZZ’) of the buoy (20), means (80) for starting the motorization means (128) and rotating its rotor (126) in order to move the floating structure (10) away from said buoy (20) when said separation distance D measured by the distance sensor (50) is less than a determined threshold. Figure for the abstract: Fig. 1

Description

An assembly comprising a floating structure, a wind turbine, and means of propelling it. Technical field of the invention

The present invention relates to a floating assembly comprising at least one floating structure connected to a submerged buoy by means of at least one flexible link, means connected to the submerged buoy for anchoring said floating structure to a seabed and a wind turbine mounted on the floating structure and comprising a propeller connected to a rotor rotating on itself around an axis of rotation.

Faced with climate change and the depletion of fossil fuel resources, an increasingly pressing and topical issue, most of the world's major powers have decided to introduce a growing share of renewable energies into their energy policies. As a result, wind power is among the two energy sources experiencing the strongest growth in terms of installed capacity annually.

A wind turbine typically consists of a tower attached to a base (concrete foundation) and rising upwards. A turbine nacelle is mounted on this tower. The nacelle contains a hub and a multi-bladed propeller (usually three blades arranged at 120° intervals). This mechanical system is complemented by a unit that converts the propeller's rotational motion into an electrical current. This unit includes components such as a brake, a gearbox, a generator/alternator, a transformer, and cables for connection to the electrical grid. Wind turbines are generally installed in fields (cultivated or uncultivated) or in designated areas, and are most often grouped together in wind farms.

However, living near these wind farms presents numerous drawbacks for residents. First, wind turbines generate noise during operation. This noise is particularly disruptive when the turbines are running at night while residents are trying to sleep. Furthermore, although efforts have been made to make them more aesthetically pleasing, wind turbines form a significant mass that can detract from the landscape and drive away local wildlife. In addition, the space required for installing a land-based wind turbine can be substantial. Therefore, it may be impossible to install a land-based wind turbine in certain locations, or a limit may be imposed on the number of turbines installed, thus reducing electricity production capacity.

To limit noise and visual pollution for local residents and improve electricity production capacity, the construction of offshore wind farms is booming worldwide following the implementation of public policies promoting renewable energy. This interest in offshore installations is explained in particular, but not exclusively, by the greater strength and consistency of wind at sea, which allows for a higher total theoretical yield (a much higher capacity factor, around 40%, compared to the average of about 30% for onshore wind power) and potentially a better return on investment.

There are few technological differences between a land-based and an offshore wind turbine. In fact, the components of the turbine itself (excluding its support structure) remain essentially the same; only increased corrosion resistance in a marine environment is required for offshore turbines. This is achieved primarily through more effective protection of the internal components and the coating applied to the external parts. Increasing the thickness of the materials used in the tower also helps to combat the regular stresses of waves and currents. Furthermore, while a land-based wind turbine is most often limited to 3.5-5 MW, an offshore wind turbine can easily provide 8-10 MW, or even 12-15 MW for very recent models. This is possible due to the quality of wind that offshore wind turbines can achieve: stronger, more consistent wind with laminar flow that is not disrupted by any topography. There are even plans to go further, always with the aim of increasing the competitiveness of offshore wind power in the energy market. Currently, there are three main types of offshore wind turbines.

The first type concerns conventional or fixed offshore wind turbines, meaning turbines similar to those installed on land, but slightly modified for use at sea. The most well-known of these consist of a fixed mast several tens of meters high (up to 150 m or even more) anchored to the seabed and supporting three blades driven by offshore or coastal winds. Each blade can be over 100 m long. Since wind direction can change, this first type of offshore wind turbine includes a turbine, generally mounted on a movable mast to adapt to the wind direction. However, the turbine represents a significant weight at the top of the turbine, which creates a considerable lever arm and can cause significant tilting stresses. Therefore, it is necessary to design an anchoring structure for the turbine that can withstand the stresses related to both the wind force and the weight of the turbine. To date, the majority of offshore wind turbines are installed on the seabed. The tower of this first type of offshore wind turbine therefore most often rests either on a metal tube driven deep into the seabed (single-pile turbine), or on a foundation (gravity-bearing concrete) consisting of a large structure placed on the seabed, or (more rarely) on a metal lattice structure called a "jacket" resting on the seabed. These first-type offshore wind turbines are generally very heavy, and their installation, particularly that of the anchoring structure, can be lengthy, costly, and complex, especially depending on weather conditions. Indeed, for an 8MW wind turbine, the penetration depth of the single pile into the seabed can exceed 30 meters for a pile diameter of approximately 8-10 meters. Regarding the gravity foundation, it may be necessary to pour more than 2000 tons of concrete, several tens of meters deep, with a footprint of several tens of meters in diameter (approximately 50-60 meters for an 8 MW wind turbine).

These wind turbines, however, do not have optimized energy efficiency. Indeed, the offshore wind turbine technique is not economically viable in waters that are too deep (40m and above – in some regions, this depth is reached very quickly close to the coast, which does not solve the problem of visual or even noise pollution), particularly due to installation and handling costs. This represents a serious obstacle to the development of wind energy.

For this reason, the scientific community has been interested for several years in floating wind turbines (FWTs), that is, turbines mounted on floats and potentially positioned far from the coast in waters several hundred meters deep (typically 100-300 meters). This technology has a construction and implementation cost that is virtually identical, regardless of the water depth. From a civil engineering perspective, FWTs are also less sensitive to the geotechnical conditions of the seabed than fixed-bottom turbines. Furthermore, their maintenance is simplified because, if necessary, they can be towed to port for repairs at the dock and under cover, even if the installation site is potentially further offshore than for a fixed-bottom turbine.

Unlike the aforementioned fixed offshore wind turbines, floating wind turbines can be installed at depths well beyond 40-50 meters, where winds are even more powerful and consistent because there is virtually no nearby terrain, further improving the capacity factor (50% and above). They consist of a floating support structure on which a mast carrying the turbine is erected. The turbine and the floating support platform can advantageously be assembled on land rather than at sea, where conditions are potentially more challenging (currents, swell, weather), before being towed to the site (with the possibility of choosing a date favorable to navigation) using a deep-sea tug for anchoring. Floating wind turbines are generally secured at their offshore installation site using anchoring systems. These systems are designed to withstand normal operating conditions and potentially more extreme ones. They generally consist of anchors (trail anchors, suction anchors, ground plates, or deadweights) and one or more mooring lines (chain, wire rope, or synthetic materials such as polyester, high-density polyethylene, or even polyamide) connected to the floating platform. SPAR (Single Point Anchor Reservoir) type floats are stabilized by their high inertia because their bottom is ballasted, which considerably increases their mass and their moments of inertia in roll and pitch. TLP (Tension Leg Platform) type floating wind turbines, on the other hand, have a platform held by tensioned anchors, so that the stiffness induced by these anchors provides high stability. Finally, the most widespread type of floating wind turbines, of the semi-submersible float type (inspired by offshore oil and gas), include a platform that is most often flat-bottomed with a shallow draft (10-20 meters in general) and unstretched anchors, its stability being ensured by Archimedes' principle.

Here again, these wind turbines are not optimized in terms of energy efficiency because they adapt poorly, if at all, to their environment due to their static position. Indeed, when using a mast, it is necessary, on the one hand, to have a very stable floating platform (therefore large, heavy, and expensive) to limit the mast's tilt (pitch and roll), and on the other hand, to limit the size of the wind turbines or their efficiency due to vibration issues and the proximity of the blades to the mast. In deep water, this technology is promising. However, the fact that the wind turbine is not anchored to the seabed significantly increases the mechanical stresses induced by waves (pitch and/or roll). In fact, during operation, these floating wind turbines are subject to currents and swells, which can induce a yaw angle in the turbine, that is, a rotation of the floating turbine around a vertical axis. These disturbances increase the float's movement and consequently the mechanical stresses on several of its components, particularly the mast, reducing their durability. This sensitivity to swell could be mitigated by increasing the float's size and weight, but this solution would increase the cost per kWh produced.

To counteract yaw, some floating wind turbine models include an electrical adjustment system. For example, electric motors or a leeward drift system allow the turbine to be rotated relative to the mast in order to (re)position the turbine's rotor axis in line with the wind.

To improve the structural strength of floating wind turbines, the patent document filed on April 18, 2013, and published under number FR3004764, describes a third type of floating wind turbine. This type comprises a floating structure that supports a horizontal-axis wind turbine using several arms rather than a single mast. The turbine nacelle is fixed relative to the floating structure, meaning it can no longer orient itself into the wind independently of the supporting floating structure to compensate for the yaw angle caused by sea forces. Instead, the entire assembly—the floating platform, the support arms, and the turbine—orients itself into the wind by rotating around an anchoring device such as a buoy or a reel. This third type therefore concerns self-orienting offshore wind turbines. These wind turbines are generally smaller and lighter than those of the first and second types.

However, because the floating structure is subject to external conditions, such as weather and especially sea state (currents, swell, waves), the efficiency and overall performance of these devices are not optimized, particularly due to the constraints mentioned above. Indeed, experiments and numerical modeling show that a floating wind turbine system using a single-point anchor can exhibit dynamic instabilities leading to a loss of electricity production and increased turbine fatigue. Specifically, the floating wind turbine can oscillate with a fishtail motion, known as fish-tailing in the prior art.

To avoid these dynamic instabilities, which are detrimental to the economic viability of floating wind turbines, a single-point anchoring system can be used with the following characteristic: Two flexible mooring lines, port and starboard, called hawsers, connect the wind turbine at its bow (port and starboard) to an offset buoy, itself anchored to the seabed by three mooring lines. The geometry of such an assembly eliminates unfavorable dynamic instabilities while minimizing the dimensions of the floating platform and therefore its cost. Mathematically, this geometry, if the length of the lines, their elasticity, and the port-starboard spacing are judiciously chosen, ensures that the real part of the mechanical system's eigenvalue projected onto the horizontal plane is negative. Generally, the wind turbine remains away from the buoy because the thrust of the turbine blades generates a force opposing, in direction, the projection onto the horizontal plane of the water surface of the axis passing through the center of the wind turbine rotor and the center of the buoy. In other, less frequent conditions, it is the drift forces generated by waves and/or currents that allow the wind turbine to remain away from the single mooring point.

However, this system presents a risk that the wind turbine may approach the buoy under certain weather conditions or during very calm periods with little or no wind, current, or swell. In such cases, the sum of the aerodynamic and/or hydrodynamic forces applied to the floating platform may change direction, meaning that the minimum safety distance between the buoy and the wind turbine is no longer guaranteed.

The invention aims, in particular, to overcome the drawbacks of the prior art cited above. More specifically, the invention aims to provide a marine energy production system that counteracts the forces of the sea and wind to optimally stabilize the wind turbine, ensuring proper turbine orientation and guaranteeing high energy production.

Presentation of the invention

The present invention aims to remedy these drawbacks with a totally innovative, high-performance, reliable, responsive approach, usable in a wide range of marine/meteorological conditions, versatile, ecological and easily adaptable.

Thus, the invention relates to a floating assembly comprising a floating support structure for at least one wind turbine, said floating structure being connected to a buoy anchored to the seabed so that this anchoring has the particularity of allowing the wind turbine to rotate around a pivot point in order to orient itself towards the wind.

Accordingly, in a first aspect, the present invention relates to a floating assembly in a marine environment for the production of electrical energy using wind, comprising:
- a floating structure comprising at least one platform equipped with a bow to which a buoy is connected by means of at least one flexible connection of the hawser type,
- means connected to the buoy for anchoring said floating structure to a seabed,
- at least one wind turbine mounted on the floating structure and comprising a supporting structure erected substantially vertically on the floating structure and supporting a multi-bladed propeller connected to a common rotor rotating on itself around an axis of rotation, and
- means for determining at least one of the following parameters: wind direction, wind speed, direction of ocean current and speed of ocean current,
characterized in that it also comprises:
- means to motorize the wind turbine's propeller in order to rotate its rotor in one direction or in the opposite direction,
- means for measuring the distance between the bow of the floating structure and a vertical axis of rotation of the buoy,
- piloting means to start the propeller's motorization means and rotate its rotor in order to move the floating structure away from said buoy when said distance measured by the distance sensor is less than a determined threshold.

The invention is implemented according to the embodiments and variants set out below, which are to be considered individually or in any technically feasible combination.

According to a complementary feature enabling improvement of the detection of the distance away and the accuracy/speed of reaction of the system for repositioning the floating platform of the wind turbine relative to the buoy, the assembly includes, in addition to means for evaluating the prediction of the azimuthal position of the floating structure relative to the buoy, and piloting means for starting up the propeller motorization means and rotating its rotor in order to move the floating structure around said buoy along its axis in a clockwise or counter-clockwise direction according to said prediction of the azimuthal position of the floating structure.

Preferably, the blades composing the propeller have means for adjusting their pitch according to the azimuthal position of each blade, so as to create an axial thrust component of the rotor collinear with the axis of said rotor and a lateral thrust component of the rotor perpendicular to the axis of said rotor.

This solution notably improves the accuracy and speed of orientation of the floating platform of the wind turbine once the distance threshold has been exceeded and the motorization means have been activated.

Advantageously, the propeller's motorization means consist of the wind turbine rotor operating in propulsion mode and connected to a main electrical energy generator operating in propulsion mode thanks to the electric machine operating in motor mode, where the electric machine usually serves in generator mode to transform wind energy into electricity.

This solution allows for the best possible integration of the motorization means in relation to the wind turbine, in particular to optimize their efficiency and responsiveness and reduce the overall weight.

In addition, the assembly also includes at least one secondary underwater bow thruster linked to the floating structure and connected to a secondary source of electrical power.

This solution further optimizes the movements of the floating assembly once the distance threshold is detected in order to reposition it in the best possible way for optimal operation of the wind turbine.

Depending on a particular characteristic, the main power generator and/or the secondary power source includes a battery.

This solution ensures the autonomy of the wind turbine's motorization system and the secondary propulsion system.

In addition, the battery is rechargeable and is connected to a photovoltaic panel attached to the floating structure or the supporting structure of the wind turbine.

Thus, propulsion systems will have an ecological, inexhaustible and easy-to-store energy source.

According to one embodiment, the main power generator and/or the secondary power source includes a fossil fuel engine such as a diesel generator.

Preferably, the main generator of electrical power and the secondary source of power are combined into a single device.

This solution allows for miniaturization of energy sources and simplification of the whole system.

According to a preferred embodiment of the present invention, the means for measuring the distance of separation comprise a GPS-type geolocation system.

According to a particular embodiment of the present invention, the means for measuring the separation distance comprise at least one detector mounted on a double-axis connector of each mooring line connecting the buoy to the floating structure and measuring a difference in inclination of the mooring line considered between a first reference position in which said mooring line is totally under tension and a second position in which said mooring line is slack in order to deduce a potential decrease in tension in said mooring line and a decrease in the separation distance.

This solution thus provides a reliable, fast, and easy-to-interpret measurement of the separation distance, guaranteeing an optimized movement of the floating assembly when this separation distance has reached the determined threshold.

According to a complementary aspect, the floating structure being connected to the buoy by two mooring lines arranged respectively on the port and starboard sides, and each mooring line having a double-axis connector, the means of measuring the separation distance D include one detector per axis of connector, i.e. four detectors in total.

This sensor duplication solution improves the accuracy of distance measurements, which can be difficult to determine, especially during large wave troughs. This sensor duplication solution also improves the robustness of distance measurements, which can be difficult to determine if one sensor fails.

According to a particularly interesting aspect of the present invention, the control means comprise at least one Proportional Integral Derivative type module adapting in real time the rotation speed of the rotor according to the measured distance distance and/or the speed of movement of the floating structure and/or the power supplied to the motorization means so that said floating structure is permanently located at a distance distance greater than or equal to the determined threshold.

This solution improves the responsiveness of the floating assembly repositioning system.

According to a complementary feature, the piloting means include two PID modules, one per hawser, collaborating with each other to control the rotational speed of the rotor and the pitch of the propeller blades.

This solution further improves the accuracy of the measurement and therefore that of the movement of the floating assembly for a smooth (without jerks) and rapid movement.

Advantageously, the buoy is statically anchored to the seabed using three flexible anchor lines spaced angularly 120° apart along a horizontal projection plane of said anchor lines.

This solution ensures a homogeneous and stable anchoring of the floating assembly.

According to a particularly interesting feature of the present invention, the means for determining the wind direction comprise at least one of the following devices chosen from an anemometer or a wind vane.

Similarly, the means of determining the direction and speed of the ocean current rely on knowledge of tidal currents according to the date and time, the use of a current meter, and knowledge of the surface area and drag coefficients of the submerged part of the floating structure.

Advantageously, the distance threshold is between approximately 80% and 90% of the nominal distance for which the mooring line connecting the floating structure to the buoy is taut.

Brief description of the figures

Other advantages, purposes and features of the present invention will become apparent from the following description, given for explanatory purposes and in no way as a limitation, with reference to the accompanying drawings, in which:

FIG. 1 there FIG. 1 is a perspective view of a floating assembly in a marine environment for the production of electrical energy using wind, according to the present invention.

FIG. 2 there FIG. 2 is a side view of the floating assembly of the FIG. 1 and consisting primarily of a floating structure and a wind turbine,

FIG. 3 there FIG. 3 is a front view of the FIG. 1 ,

FIG. 4 there FIG. 4 is a top view of the FIG. 1 ,

FIG. 5 there FIG. 5 is a detailed view of part of the floating assembly shown in figures 1 to 4,

FIG. 6 there FIG. 6 is a side view of the assembly in which the platform is in a different position than in figures 1 to 5,

FIG. 7 there FIG. 7 is a detailed view of the FIG. 6 , And

FIG. 8 there FIG. 8 is a variant implementation of the FIG. 5 .

This description is not exhaustive, as each feature of one embodiment can be combined with any other feature of any other embodiment.

It should be noted from the outset that the figures are not necessarily to scale, without this hindering their understanding.

Figures 1 to 5 represent a floating assembly 1 for the production of electrical energy using wind, in particular of the offshore type, comprising a floating structure 10 having at least one platform 11 provided with a bow 12 connected to a submerged buoy 20 by means of at least one flexible hawser 30, and preferably two hawsers 30 as shown,
- 40 wire-type means connected to the buoy 20 to anchor said floating structure 10 to a seabed 5, and
- at least one wind turbine 100 mounted on the floating structure 10 and comprising mainly a supporting structure 110 erected substantially vertically on the floating structure 10 and supporting a propeller 120 with several blades 122 connected to a common rotor 124 rotating on itself around an axis of rotation XX'.

The platform 11 of the floating structure 10 is of a known type and comprises, for example, welded steel beams resistant to marine corrosion and supported, for example, by submerged flotation caissons. This platform 11 has a basic square shape with four corners 15 and measures approximately 50 meters on each side, with a height, including the submerged flotation caissons, of approximately 25 to 30 meters, for a power output of 5 MW. For a 20 MW wind turbine, the length of the float is approximately 80 meters. Other shapes are of course possible, for example, rectangular. The draft of the floating structure 10 is determined using the flotation caissons (ballast) and can be adapted, if necessary, to the offshore location of the power generation unit 1, particularly according to the water depth, the distance from the coast, and wave conditions.

Buoy 20 is connected to two points spaced 13 and 14 on the bow 12 of platform 11 by means of two identical hawsers 30 so as to form an isosceles triangle.

The buoy 20 is typically positioned approximately 100-110 meters from the bow 12 of the platform 11, for example, about 105 meters. Given the width of the platform 11 and the height of the mooring points 13 and 14 relative to water level E, the mooring lines 30 are each approximately 110 to 120 meters long when fully tensioned. An electrical cable 35 also connects the submerged buoy 20 to the platform 11 to transmit the electricity produced by the wind turbine 100 during its operation, or to store it in gaseous or liquid form in a tank (not shown) placed on the platform 11 (which may then have a floor extending between welded beams) for later use. The buoy 20 is also equipped with a cable 36 connected to the shore to carry the generated electrical energy. Buoy 20 can be fully submerged below water level E in certain configurations.

As can be seen in Figures 1 to 4, the buoy 20 is also firmly anchored to the seabed 5 by means of three other mooring lines 40, including, for example, a long frontal line (approximately 500 to 600 meters) and two identical shorter lateral lines (approximately 140 to 150 meters). Other dimensions are perfectly feasible depending on the topography of the seabed 5 where it is installed. These three mooring lines 40 are preferably arranged, when viewed from the zenith of the buoy 20 (along the axis ZZ'), at 120° angles to each other, as illustrated in the FIG. 4 These three mooring lines 40 thus hold the buoy 20 in a substantially static position, but it can oscillate up and down along the vertical axis ZZ' according to the swell. The buoy 20 therefore defines a substantially fixed point (except vertically) for the mooring of the floating structure 10 of the electrical power generation unit 1.

Wind turbine 100 comprises a supporting structure 110, in this case consisting of four uprights/posts connecting the four corners 15 of the platform 11 and converging at a common apex 124 to form a five-sided pyramid (a lower face formed by the base of the platform 11 and four identical lateral faces formed by two adjacent uprights together defining an isosceles or equilateral triangle). The height to the apex of this supporting structure 110 of wind turbine 100 above sea level is approximately 85 to 90 meters for a 5 MW wind turbine, and approximately 160-180 m for a 20 MW wind turbine.

The axis XX' of rotation of the rotor 124, which supports the blades 122 of the propeller 120 of the wind turbine 100, passes substantially through the apex of the pyramidal support structure 110. This axis is also substantially parallel to the plane defined by the platform 11 (a plate connecting the corners 15 of the welded beams of the floating structure 10 can form a floor if necessary). Thus, in the upright and perfectly vertical position of the wind turbine 100 (with the platform 11 horizontal), the axis XX' of rotation of the rotor 124 is itself horizontal. The blades 122, as they rotate, describe a circle with a diameter of approximately 100 to 120 m, so that the highest point of the blades 122 is approximately 150 to 160 m above the water level E for a 5 MW wind turbine and approximately 320 m for a 20 MW wind turbine.

According to the present invention, the floating energy production assembly also includes means 60 and 70 for determining at least one of the following parameters: wind direction, wind speed, direction of the ocean current, and speed of the ocean current. In this case, the means 60 for determining the wind direction include at least one of the following accessories, selected from an anemometer, a LIDAR, or a wind vane, fixedly placed at the top of the wind turbine 100, that is, at a height sufficiently high to accurately measure the winds that can influence the movement of the supporting structure 10 by acting on the blades 122.

The means 70 for determining the direction and speed of the marine current consist of an immersed current meter type sensor connected to the platform 11 and connected to a control computer 80 containing, for example, a knowledge base of tidal currents according to the date and time, and of the surface and drag coefficients of the submerged part of the floating structure 10.

Finally, the electrical power production assembly 1 according to the present invention includes a complex system for the automatic repositioning of the floating platform 10 relative to the buoy 20, which will be explained in more detail below.

For this purpose, set 1 comprises:
- means 128 for motorizing the propeller 120 of the wind turbine 100 in order to rotate its rotor 126 in one direction of rotation or in the opposite direction,
- means 50 for measuring the distance D between the bow 12 of the floating structure 10 and the vertical axis of rotation ZZ' of the buoy 20, and
- control means 80, for example a computer) to start the means 128 for motorizing the propeller 120 and to rotate its rotor 126 in order to move the floating structure 10 away from the buoy 20 when said separation distance D measured by the distance sensor 50 is less than a determined threshold.

According to a particular feature of the invention, the means 128 for motorizing the propeller 120 consist of the motor 128 of the rotor 126 of the wind turbine operating in propulsion mode and connected to a main electrical power generator 129 of the battery type or diesel generator or export electrical cable type.

The means 50 for measuring the separation distance D include at least one detector 51 mounted on a double-axis connector of each mooring line 30 connecting the buoy 20 to the floating structure 10 and measuring a difference in inclination α of the mooring line 30 between a first reference position in which said mooring line 30 is fully under tension and a second position in which said mooring line 30 is slack in order to deduce a potential decrease in tension in said mooring line and a decrease in the separation distance D. In the present case, and in order to improve the measurements, each mooring line 30 has two double-axis connectors, each equipped with a detector 51 per axis, i.e. four separation detectors 50 in total.

In order to refine the efficiency of the system, assembly 1 also includes means 90 for evaluating the azimuthal position prediction of the floating structure 10 relative to the buoy 20, for example an inertial measurement unit, a magnetometer or a set of differential GPS and piloting means 80 for starting up the motorization means 128 of the propeller 120 and turning its rotor 126 in order to move the floating structure 10 around said buoy 20 along the axis ZZ’ in a clockwise or counterclockwise direction according to said azimuthal position prediction of the floating structure.

To this end, the blades 122 composing the propeller 120 have means 130 for adjusting their pitch according to the azimuthal position of each blade 122 so as to create an axial thrust component of the rotor 126 collinear with the axis XX’ of said rotor 126 and a lateral thrust component of the rotor 126 perpendicular to the axis XX’ of said rotor 126. By varying the pitch of each of the blades according to their azimuthal position, for example sinusoidally with respectively 10°, 0°, -10°, 0° for azimuthal positions of 0°, 90°, 180°, 270°, the rotor generates a lateral thrust sufficient to move the structure. The angle of attack of the blades 122 is adjusted to generate an axial/lateral thrust that will move the wind turbine backward relative to the buoy 20 and tighten the mooring lines 30. The axial/lateral thrust is regulated to maintain a sufficient distance D while minimizing the required electrical consumption (which remains negligible compared to the amount of energy produced by the wind turbine in production mode, for example, approximately 60W for a nominal power of 4 kW). The direction of the lateral thrust is chosen to minimize the energy and the length of the arc of a circle to be traveled to reach a stabilized position.

These adjustment means can be supplemented by two secondary underwater bow thrusters 95 and 96 connected to the platform 11 and connected to a secondary source of electrical power 98 such as a battery (the same as that of the propulsion means 128 of the wind turbine 100) or a diesel generator.

Finally, the piloting means 80 include at least one Proportional-Integral-Derivative (PID) module that adapts in real time the rotational speed of the rotor 126 according to the measured distance D and/or the speed of movement of the floating structure 10 and/or the power supplied to the propulsion means 128 so that said floating structure 10 is constantly located at a distance D greater than or equal to the determined threshold. It is even planned that the piloting means 80 will include two PID modules, one per mooring line 30, working together to control at least one of the following parameters: the rotational speed of the rotor 126, the pitch of the propeller blades 122, and the power of the secondary underwater bow thrusters 95 and 96.

There FIG. 8 shows another type of structure called "upwind" (with vertical face and wind coming from the front) in which the blades 122 of the wind turbine 100 do not rotate in the center of the pyramid formed by the supporting structure 110 but outside and on the front of the tubular structure 110. Nevertheless, the same means as those described in relation to figures 1 to 7 are used for the same objective.

As explained in the introduction, it sometimes happens that the floating structure 10 unintentionally approaches the buoy 20 (arrow F of the FIG. 6 ), whether the blades 122 of the propeller 120 are rotating (energy production mode) or not.

This phenomenon has been studied extensively by the applicant according to the protocol described below.

Indeed, due to their anchoring system based on single-point mooring (SPM), floating offshore wind turbines are subject to potentially dangerous movements in low wind conditions. Specifically, the thrust applied to the rotor 124 when the blades 122 of the turbine 100 generate electrical energy is greater than the drag force induced by the current. The float 10 therefore naturally aligns itself with the wind direction. For wind speeds below 4 m/s, the blades 122 of the turbine 100 are stopped, and the resulting thrust tends to be less than the current drag. The float 10 therefore tends to align itself with the direction of the current with an uncontrolled trajectory after the rotation of the blades 122 of the wind turbine 100 has stopped. This can lead to one of the mooring lines 30 getting caught on the mooring lines or the electric cable, or, in the worst case, a collision between the float 10 and the buoy 20.

To identify the environmental conditions under which the control system 80 (also referred to as the system in this description) should be activated, a load case table including low winds and opposing currents was used. Time series of results were extracted from a measurement database and used as baseline environmental data to evaluate system performance. This data comes from a first measurement campaign (A) lasting seven years, which began in 2012 and ended in 2019 with hourly data sampling, followed by a second measurement campaign (B) lasting three months, conducted in 2013 with 10-minute data sampling. The data thus collected allows for the creation of a graph representing the current speed in m/s, in a range from 0 to over 1.2, and the wind speed in m/s in a range from 0 to over 25 m/s.

With particular interest in high wind and current transients, studies based on a selection of wind/current data from campaign B (to have a smaller sampling rate and higher resolution) were carried out and a selection was made to identify cases in which the wind speed is less than 5 m/s and the wind direction relative to the current is greater than 90°.

It was thus possible to highlight 47 different cases which can be classified into 3 categories, namely static conditions of the type with low wind and low current, in which the system 80 according to the invention must be used to compensate for the residual tension of the mooring lines 30 which tend to attract the float 10 towards the buoy 20, conditions of predominance of the current over the wind in which the wind turbine 100 is in mode of producing electrical energy, and conditions of predominance of the wind over the current in which the wind turbine 100 is stopped.

Following a selection process, 13 of these 47 cases were studied in more detail, covering the three categories presented above. Most of the identified load cases involve current velocities ranging from 0.05 m/s to 0.3 m/s. Only one load case exhibits current velocities up to 0.6 m/s.

Study A shows that the current can reach speeds of up to 1.1 m/s. This second study provides a larger, more representative sample of current speeds. The selection process in this second study allows us to extract eight cases in which the transients exhibit a current speed greater than 0.5 m/s and a wind direction relative to the current greater than 90°.

All this data is collected and entered into an Orcaflex® simulation platform. In the absence of any system conforming to the present invention, the simulation highlights several critical situations where the float 10 approaches the buoy 20 to varying degrees and at varying speeds (arrow F of the FIG. 6 During these events, the two hawsers 30 tend to slacken. This can be measured by their inclination relative to the horizontal.

When the hawser 30 is properly tensioned, the angle α is zero on the FIG. 6 or 7, when the mooring line slackens and releases, the angle α is then strictly greater than 0°, for example approximately 5 to 30°, and more specifically between approximately 10 and 20°, depending on the degree of slack in the mooring line 30, which may even come into contact with the water's surface E. When the angle α begins to exceed 10°, this means that the bow 12 of the platform 11 has already moved several meters closer to the buoy 20 and that the system 80 must be activated.

The threshold distance D at which system 80 activates (preferably automatically) is considered to be between approximately 80% and 90% of the nominal distance at which the connecting mooring line 30 from the floating structure 10 to the buoy 20 is under maximum tension (without stretching the mooring line, i.e., normal tension with the line perfectly straight). Thus, if the nominal distance D between the bow and the axis ZZ' is approximately 100 m, then system 80 will begin to activate as soon as this distance D reaches 80 to 90 m.

This study shows that the mooring lines 30 slack primarily when the current speed is less than or equal to 0.3 m/s. Critical situations are rare when the current speed is higher (0.3 m/s and above). This can be explained by the fact that the float 10 easily aligns with the current direction when the current speed is high, while the mooring lines 30 tend to pull the float 10 towards the buoy 20 when the current is weak. Nevertheless, a strong current flowing in the opposite direction to the wind can be problematic during the transitional phase when the wind turbine 100 is stopped.

The invention thus makes it possible to maintain the float 10 at a desired distance from the buoy 20 with the two hawsers 30 taut. In certain situations, the invention also has the capacity to move the float 10 to a safe location where it will not be at risk of crashing by applying a longitudinal and lateral force to it.

This role is fulfilled by two actuator systems, namely:
- the 100 wind turbine used in motor mode if the energy production device is connected to the grid, and
- two auxiliary thrusters 95 and 96, one longitudinal and the other lateral, if the power generation device 1 is not connected to the network.

The 100 wind turbine used in motor mode aims to generate longitudinal and lateral forces through the combination of two controls:
- Use the converter to drive the electrical machine as a motor instead of a generator, and
- Use individual pitch control (IPC) to change the pitch of the 122 blades in a part of the rotating disk in order to generate lateral movement.

More precisely, when the sum of the 2 vectors presented below at time t, or the predicted sum in the next few hours, indicates that float 10 is likely to move closer to buoy 20:
- the vector representing the wind thrust (estimated using an anemometer, a wind vane, the rotor's rotation speed, the angle of attack of each blade, knowledge of the surface area and drag coefficients of the above-water part of the hull, masts and nacelle, and knowledge of wind forecasts), and
- the vector representing the current thrust (estimated using knowledge of tidal currents based on date and time, a current meter, and knowledge of the surface area and drag coefficients of the submerged part of the hull),
- or when the redundant 50 means of measuring inclination (inclinometers) placed on the mooring lines measure 30 an angle α exceeding a certain threshold (for example 5° or 10° depending on the length of the mooring lines 30 / the nominal distance D).

So, the motor mode of rotor 124 of wind turbine 100 is activated, if it is connected to the grid. Otherwise, bow thrusters 95 and 96, powered by a backup power source (batteries or diesels), can be activated on the prototype.

Software is used to integrate all the measurements necessary to control the 100-watt wind turbine in motor mode. According to a diagram developed by the applicant, the software comprises five main blocks, namely:
- an estimation block that calculates variables that cannot be measured (e.g., thrust, hydrodynamic drag...), these variables being used by a controller block,
- a supervisory block that defines the operating mode of system 80 according to the demands of a SCADA (Supervisory Control And Data Acquisition) real-time control and data acquisition system, input data and alarm signals, and that selects the actuator system to use,
- a detection block that allows the control strategy to be used according to environmental conditions (wind direction and strength, current strength and direction),
- a control block that calculates the longitudinal and lateral force commands to be applied, and
- an actuator block converts these force commands into blade pitch commands 122 and rotor speed commands 126 for motor mode, or into power for each of the thrusters 95 and 96.

It must be clearly understood that the detailed description of the object of the Invention, given solely as an illustration, does not in any way constitute a limitation, technical equivalents also being included in the scope of the present invention.

Thus, the floating platform 10 could serve as a support for several wind turbines 100 and no longer just one.

Claims (17)

Assembly (1) floating in a marine environment for the production of electrical energy using wind comprising:
- a floating structure (10) comprising at least one platform (11) equipped with a bow (12) to which a buoy (20) is connected by means of at least one flexible hawser-type connection (30),
- means (40) connected to the buoy (20) for anchoring said floating structure (10) to a seabed (5),
- at least one wind turbine (100) mounted on the floating structure (10) and comprising a supporting structure (110) erected substantially vertically on the floating structure (10) and supporting a propeller (120) with several blades (122) connected to a common rotor (126) rotating on itself around an axis of rotation (XX'), and
- means (60; 70) for determining at least one of the following parameters among wind direction, wind speed, direction of ocean current and speed of ocean current,
characterized in that it also comprises:
- means (128) for motorizing the propeller (120) of the wind turbine (100) in order to rotate its rotor (126) in one direction of rotation or in the opposite direction,
- means (50) for measuring the distance D between the bow (12) of the floating structure (10) and a vertical axis of rotation (ZZ') of the buoy (20),
- piloting means (80) to start the propeller (120) motorization means (128) and rotate its rotor (126) in order to move the floating structure (10) away from said buoy (20) when said separation distance D measured by the distance sensor (50) is less than a determined threshold. Assembly (1) according to claim 1, characterized in that it further comprises:
– means (90) for evaluating the predicted azimuthal position of the floating structure (10) relative to the buoy (20),
- piloting means (80) to start the motorization means (128) of the propeller (120) and rotate its rotor (126) in order to move the floating structure (10) around said buoy (20) along the axis (ZZ') clockwise or counterclockwise according to said azimuthal position prediction of the floating structure (10). Assembly (1) according to claim 2, characterized in that the blades (122) composing the propeller (120) have means (130) for adjusting their pitch as a function of the azimuthal position of each blade (122), so as to create an axial thrust component of the rotor (126) collinear with the axis (XX') of said rotor (126) and a lateral thrust component of the rotor (126) perpendicular to the axis (XX') of said rotor (126). Assembly (1) according to any one of the preceding claims, characterized in that the propeller (120) motorization means (128) consist of the motor (128) of the rotor (126) of the wind turbine operating in propulsion mode and connected to a main electric power generator (129). Assembly (1) according to any one of the preceding claims, characterized in that it further comprises at least one secondary underwater bow thruster (95; 96) linked to the floating structure (10) and connected to a secondary source of electrical power (98). Assembly (1) according to claims 4 and 5, characterized in that the main electric power generator (129) and/or the secondary electric power source (98) comprise(s) a battery. Assembly (1) according to claims 4 and 5, characterized in that the main electric power generator (129) and/or the secondary power source (98) comprise(s) a fossil fuel engine such as a diesel generator. Assembly (1) according to claim 6 or claim 7, characterized in that the main electric power generator (129) and the secondary electric power source (98) are combined into a single device. Assembly (1) according to any one of the preceding claims, characterized in that the means (50) for measuring the distance D comprise a GPS-type geolocation system. Assembly (1) according to any one of claims 1 to 8, characterized in that the means (50) for measuring the separation distance D comprise at least one detector (51) mounted on a double-axis connector of each mooring line (30) connecting the buoy (20) to the floating structure (10) and measuring a difference in inclination (α) of the mooring line considered (30) between a first reference position in which said mooring line (30) is totally under tension and a second position in which said mooring line (30) is slack in order to deduce a potential decrease in tension in said mooring line and a decrease in the separation distance D. Assembly (1) according to claim 10, characterized in that , the floating structure (10) being connected to the buoy (20) by two mooring lines (30) arranged respectively on the port and starboard sides, and each mooring line (30) comprising two double-axis connectors, the means for measuring the separation distance D comprise a detector (51) per connector axis, i.e. four detectors in total. Assembly (1) according to any one of the preceding claims, characterized in that the control means (80) comprise at least one Proportional Integral Derivative (PID) type module adapting in real time the rotation speed of the rotor (126) as a function of the measured distance D and/or the speed of movement of the floating structure (10) and/or the power supplied to the drive means (128) so that said floating structure (10) is permanently located at a distance D greater than or equal to the determined threshold. Assembly (1) according to claims 11 and 12, characterized in that the piloting means (80) comprise two PID modules, one per hawser (30), collaborating with each other to control the rotational speed of the rotor (126) and the pitch of the blades (122) of the propeller (120). Assembly (1) according to any one of the preceding claims, characterized in that the buoy (20) is statically anchored to the seabed (5) by means of three flexible anchor lines (40) spaced angularly apart from each other by 120° along a horizontal projection plane of said anchor lines. Assembly (1) according to any one of the preceding claims, characterized in that the means (60) for determining the wind direction comprise at least one of the following devices selected from an anemometer or a wind vane. Assembly (1) according to any one of the preceding claims, characterized in that the means (70) for determining the direction and speed of the marine current are based on knowledge of tidal currents as a function of date and time, the use of a current meter, and knowledge of the surface area and drag coefficients of the submerged part of the floating structure. Assembly (1) according to any one of the preceding claims, characterized in that the separation distance threshold D is between approximately 80% and 90% of the nominal distance for which the connecting hawser (30) of the floating structure (10) to the buoy (20) is stretched.